TY - JOUR
AU1 - Oresanya, T. F.
AU2 - Beaulieu, A. D.
AU3 - Patience, J. F.
AB - Abstract Much of our understanding of energy metabolism in the pig has been derived from studies in which the energy supply was controlled through regulated feed intake. In commercial situations, where ad libitum feeding is practiced, dietary energy concentration, but not daily feed intake, is under producer control. This study evaluated the interactive effects of dietary energy concentration and feeding level (FL) on growth, body composition, and nutrient deposition rates. Individually penned PIC barrows, with an initial BW of 9.5 ± 1.0 kg, were allotted to 1 of 9 treatments in a 3 × 3 factorial arrangement plus an initial slaughter group (n = 6) that was slaughtered at the beginning of the trial. Three NE concentrations (low, 2.15; medium, 2.26; and high, 2.37 Mcal of NE/kg) and 3 feeding levels (FL: 100, 80, or 70% of ad libitum access to feed) were investigated. Daily feed allowance for the restricted-fed pigs was adjusted twice per week on a BW basis until completion of the experiment at 25 ± 1 kg of BW. Average daily gain, ADFI, and G:F were unaffected by NE (mean = 572 g, 781 g, and 0.732 g/g, respectively). Average daily gain and ADFI, but not G:F, increased (P < 0.05) with FL. Empty body lipid concentration increased with dietary NE concentration and with FL; a significant (P < 0.01) interaction revealed that empty body lipid concentration increased most rapidly as ADFI increased on the highest energy diet. Empty body lipid concentration was greatest in pigs with ad libitum access to the high-NE diet. Empty body protein concentration decreased with increasing NE (P < 0.05) but was not affected by FL. Empty body protein deposition (PD) increased with increasing FL (P < 0.001), but not with NE. Empty body lipid deposition (LD) and the LD:PD ratio increased (P < 0.01) in pigs with ad libitum access to the high-NE diet. In conclusion, NE did not interact with FL on growth, body protein concentration, or PD, suggesting that the conclusions regarding energy utilization obtained from experiments using restricted feed intake may not easily be applied to pigs fed under ad libitum conditions. The interactive effects of NE and FL on body lipid concentration, LD, and the LD:PD ratio indicate that changes in dietary energy concentration alter the composition of gain without necessarily changing overall BW gain. Consequently, the composition of gain is an important outcome in studies on energy utilization. INTRODUCTION Much of our understanding of energy metabolism in the pig has been derived from studies in which energy supply was controlled through regulated feed intake. Ad libitum feeding is practiced in much of the world; thus, under commercial circumstances, dietary energy concentration, but not daily feed intake, is under producer control. A complete understanding of how the pig utilizes dietary energy requires a simultaneous and detailed evaluation of the impact of dietary energy concentration and daily energy intake on growth and body composition. The literature is limited on the impact of changing energy intake through the control of daily feed intake in the weanling pig. However, we can infer from studies using the growing pig (e.g., Bikker et al., 1995; Quiniou et al., 1995) that both protein-dependent and energy-dependent phases of growth probably exist. The hypothesis tested in this experiment was that there would be a difference between the response of the weanling pig resulting from changes in dietary NE concentration vs. the response resulting from changes in feed (energy) intake. The main objective of this experiment was to determine whether an interaction would be observed between daily energy intake and dietary NE concentration on BW gain and on tissue (protein, lipid, ash, water) accretion rates and ratios and on plasma IGF-I concentration. A secondary objective was to determine whether measured DE intake (DEi) or calculated NE intake (NEi; based on Centraal Veevoederbureau, 1994, 1998) is more effective in predicting animal growth performance. MATERIALS AND METHODS All procedures used in this experiment were approved by the University of Saskatchewan Committee on Animal Care and Supply and adhered to principles established by the Canadian Council on Animal Care (1993). The experiment involved 3 all-in–all-out nursery rooms equipped with automatic light timers (12-h light:12-h dark cycle) and integrated controllers (Model PEC, Phason, Winnipeg, Manitoba, Canada) regulating the heating and ventilation systems. Room temperature was initially set at 29°C at weaning and gradually decreased by 1.5°C/wk. All pens (1.27 × 1.04 m) were equipped with fully slatted floors, a single nipple drinker, and an adjustable multiple-space dry feeder. The feeders were checked daily for proper feed flow to minimize wastage, and the drinkers were checked for adequate water flow. Animals, Treatments, and Experimental Design A growth and comparative slaughter trial was conducted with the castrated male offspring of C-22 females × 337 sires (PIC Canada Ltd., Winnipeg, Manitoba, Canada). The experiment was conducted in 3 replicates of 27 pigs each plus the initial slaughter group (ISG; n = 6). This provided a total of 87 barrows used in this experiment. Treatments were arranged as a 3 × 3 factorial, with 3 diets and 3 feed intake levels. Diets were formulated to contain 2.21, 2.32, and 2.42 Mcal of NE/kg (as-fed basis; Centraal Veevoederbureau, 1998). Three feed intake levels were used, corresponding to 100, 80, or 70% of ad libitum feed intake. These levels of restriction, and the nature of the design, were validated in a previous experiment (Oresanya, 2005). Feed intake levels in the limit-fed pigs (80 or 70% of ad libitum feed intake) were based on the intake of pigs fed on an ad libitum basis within replicate. Before the first weighing period, completed on d 4 of the experiment, the feed intake of the control pigs was unavailable, so for this period alone, the restricted intakes were based on the data derived from other experiments using the same age of pig within the same barn (Oresanya et al., 2003, 2007). For limit-fed pigs, the total daily feed allowance was provided in a single morning feeding. Before the beginning of the experiment, pigs were allowed ad libitum access to a pelleted commercial phase-1 starter diet (Ultrawean 21, Coop Feeds, Saskatoon, Saskatchewan, Canada) for the first 6 d post-weaning, followed by a pelleted phase-2 starter diet (GI MAX 21, Coop Feeds, Saskatoon, Saskatchewan, Canada) for the next 4 d. All available pigs were weighed on d 7 postweaning, and the most uniform animals, based on BW, weight per day of age, and postweaning ADG (8.5 ± 0.9 kg, 0.298 ± 0.041 kg/d, 0.164 ± 0.080 kg/d, respectively; mean ± SD) were selected. Pigs were blocked and randomly assigned to experimental treatments, and the ISG was selected based on BW. Experimental Diets Experimental diets (Table 1) were formulated to contain increasing levels of NE, based on Centraal Veevoederbureau (1998) NE values of the ingredients. The target NE concentration was 2.21 to 2.42 Mcal/kg; on analysis, the calculated NE concentrations were 2.15 (low), 2.26 (medium), and 2.37 (high) Mcal of NE/kg. Differences in NE concentration were achieved by a gradual reduction of CP concentration from 29.0 to 24.7% and crude fiber from 3.0 to 2.4%. Fat concentration was increased from 3.5 to 5.4% in the low- to high-NE diets. The diets contained celite added at 0.5% as a source of exogenous acid insoluble ash, to serve as an indigestible marker. The calculated and analyzed nutrient composition of the experimental diets is reported in Table 2. Table 1. Ingredient composition of the experimental diets, as-fed basis1   Formulated NE concentration, Mcal/kg  Ingredient, %  2.21  2.32  2.42  Wheat  51.89  57.70  63.24  Soybean meal  27.00  19.25  11.50  Menhaden fish meal  8.50  8.50  8.50  Soy protein concentrate2  2.25  2.25  2.25  Dried-skim milk  2.50  2.50  2.50  Lactose3  5.00  5.00  5.00  Canola oil  0.50  1.75  3.00  Limestone  0.34  0.42  0.50  Salt  0.30  0.30  0.30  Mineral premix4  0.50  0.50  0.50  Vitamin premix5  0.50  0.50  0.50  Choline chloride  0.05  0.05  0.05  Celite6  0.50  0.50  0.50  NaHC \(O_{3}^{7}\)   —  —  0.28  L-Lys·HCl  —  0.29  0.59  L-Thr  0.04  0.17  0.30  DL-Met  0.04  0.13  0.22  L-Trp  —  0.03  0.07  L-Val  —  0.05  0.09  L-Ile  —  0.01  0.02  LS 208  0.10  0.10  0.10    Formulated NE concentration, Mcal/kg  Ingredient, %  2.21  2.32  2.42  Wheat  51.89  57.70  63.24  Soybean meal  27.00  19.25  11.50  Menhaden fish meal  8.50  8.50  8.50  Soy protein concentrate2  2.25  2.25  2.25  Dried-skim milk  2.50  2.50  2.50  Lactose3  5.00  5.00  5.00  Canola oil  0.50  1.75  3.00  Limestone  0.34  0.42  0.50  Salt  0.30  0.30  0.30  Mineral premix4  0.50  0.50  0.50  Vitamin premix5  0.50  0.50  0.50  Choline chloride  0.05  0.05  0.05  Celite6  0.50  0.50  0.50  NaHC \(O_{3}^{7}\)   —  —  0.28  L-Lys·HCl  —  0.29  0.59  L-Thr  0.04  0.17  0.30  DL-Met  0.04  0.13  0.22  L-Trp  —  0.03  0.07  L-Val  —  0.05  0.09  L-Ile  —  0.01  0.02  LS 208  0.10  0.10  0.10  1 Calculated NE concentrations were based on the NE value of ingredients (Centraal Veevoederbureau, 1998). Soybean meal, fish meal, and skim milk powder were assayed for CP and AA composition prior to diet formulation. Amino acid analysis was conducted according to the methods of Llames and Fontaine (1994; Degussa Corporation, Amino Acid Laboratory, Allendale, NJ). 2 Soy protein concentrate, Profine E, Central Soya Co., Decatur, IN. 3 Prolac (83% lactose), Univar Canada Ltd., Richmond, British Columbia, Canada. 4 Provided per kilogram of diet: Zn, 100 mg as zinc sulfate; Fe, 80 mg as ferrous sulfate; Cu, 50 mg as copper sulfate; Mn, 25 mg as manganous sulfate; I, 0.50 mg as calcium iodate; and Se, 0.10 mg as sodium selenite. 5 Provided per kilogram of diet: vitamin A, 8,250 IU; vitamin D3, 825 IU; vitamin E, 40 IU; niacin, 35 mg; D-pantothenic acid, 15 mg; riboflavin, 5 mg; menadione, 4 mg; folic acid, 2 mg; thiamine, 1 mg; D-biotin, 0.2 mg; and vitamin B12, 25 μg. 6 Celite (Celite Corporation, Lompoc, CA), provided as a source of acid insoluble ash. Typical percentage of physical composition: moisture, 0.8; SiO2, 89.4; Na2O, 3.8; Al2O3, 3.4; Fe2O3, 1.3; MgO, 0.6; CaO, 0.5; and TiO2, 0.2 (Megazyme International Ireland Ltd., Bray, Co. Wicklow, Ireland). 7 Added to maintain a dietary electrolyte balance above 225 mEq/ kg among the diets (Patience et al., 1987). 8 Provided lincomycin at 22 g/kg and spectomycin at 22 g/kg (Bio-Agrimix, Mitchell, Ontario, Canada). View Large Table 1. Ingredient composition of the experimental diets, as-fed basis1   Formulated NE concentration, Mcal/kg  Ingredient, %  2.21  2.32  2.42  Wheat  51.89  57.70  63.24  Soybean meal  27.00  19.25  11.50  Menhaden fish meal  8.50  8.50  8.50  Soy protein concentrate2  2.25  2.25  2.25  Dried-skim milk  2.50  2.50  2.50  Lactose3  5.00  5.00  5.00  Canola oil  0.50  1.75  3.00  Limestone  0.34  0.42  0.50  Salt  0.30  0.30  0.30  Mineral premix4  0.50  0.50  0.50  Vitamin premix5  0.50  0.50  0.50  Choline chloride  0.05  0.05  0.05  Celite6  0.50  0.50  0.50  NaHC \(O_{3}^{7}\)   —  —  0.28  L-Lys·HCl  —  0.29  0.59  L-Thr  0.04  0.17  0.30  DL-Met  0.04  0.13  0.22  L-Trp  —  0.03  0.07  L-Val  —  0.05  0.09  L-Ile  —  0.01  0.02  LS 208  0.10  0.10  0.10    Formulated NE concentration, Mcal/kg  Ingredient, %  2.21  2.32  2.42  Wheat  51.89  57.70  63.24  Soybean meal  27.00  19.25  11.50  Menhaden fish meal  8.50  8.50  8.50  Soy protein concentrate2  2.25  2.25  2.25  Dried-skim milk  2.50  2.50  2.50  Lactose3  5.00  5.00  5.00  Canola oil  0.50  1.75  3.00  Limestone  0.34  0.42  0.50  Salt  0.30  0.30  0.30  Mineral premix4  0.50  0.50  0.50  Vitamin premix5  0.50  0.50  0.50  Choline chloride  0.05  0.05  0.05  Celite6  0.50  0.50  0.50  NaHC \(O_{3}^{7}\)   —  —  0.28  L-Lys·HCl  —  0.29  0.59  L-Thr  0.04  0.17  0.30  DL-Met  0.04  0.13  0.22  L-Trp  —  0.03  0.07  L-Val  —  0.05  0.09  L-Ile  —  0.01  0.02  LS 208  0.10  0.10  0.10  1 Calculated NE concentrations were based on the NE value of ingredients (Centraal Veevoederbureau, 1998). Soybean meal, fish meal, and skim milk powder were assayed for CP and AA composition prior to diet formulation. Amino acid analysis was conducted according to the methods of Llames and Fontaine (1994; Degussa Corporation, Amino Acid Laboratory, Allendale, NJ). 2 Soy protein concentrate, Profine E, Central Soya Co., Decatur, IN. 3 Prolac (83% lactose), Univar Canada Ltd., Richmond, British Columbia, Canada. 4 Provided per kilogram of diet: Zn, 100 mg as zinc sulfate; Fe, 80 mg as ferrous sulfate; Cu, 50 mg as copper sulfate; Mn, 25 mg as manganous sulfate; I, 0.50 mg as calcium iodate; and Se, 0.10 mg as sodium selenite. 5 Provided per kilogram of diet: vitamin A, 8,250 IU; vitamin D3, 825 IU; vitamin E, 40 IU; niacin, 35 mg; D-pantothenic acid, 15 mg; riboflavin, 5 mg; menadione, 4 mg; folic acid, 2 mg; thiamine, 1 mg; D-biotin, 0.2 mg; and vitamin B12, 25 μg. 6 Celite (Celite Corporation, Lompoc, CA), provided as a source of acid insoluble ash. Typical percentage of physical composition: moisture, 0.8; SiO2, 89.4; Na2O, 3.8; Al2O3, 3.4; Fe2O3, 1.3; MgO, 0.6; CaO, 0.5; and TiO2, 0.2 (Megazyme International Ireland Ltd., Bray, Co. Wicklow, Ireland). 7 Added to maintain a dietary electrolyte balance above 225 mEq/ kg among the diets (Patience et al., 1987). 8 Provided lincomycin at 22 g/kg and spectomycin at 22 g/kg (Bio-Agrimix, Mitchell, Ontario, Canada). View Large Table 2. Calculated and analyzed nutrient content of the experimental diets, as-fed basis1   Formulated NE concentration, Mcal/kg  Nutrient  2.21  2.32  2.42  Calculated      ME, Mcal/kg  3.26  3.32  3.37      DE, Mcal/kg  3.48  3.53  3.57      DM, %  89.42  89.51  89.63      CP,2 %  28.29  25.94  23.55      Crude fat, %  2.17  3.97  5.22      Crude fiber, %  2.68  2.58  2.48      Total Lys,2 %  1.63  1.65  1.67      TID Lys,3 %  1.47  1.51  1.55      TEAAN,4 %  1.90  1.76  1.62      TEAAN:TNEAAN5  0.72  0.74  0.76      dEB,6 mEq/kg  303  254  238  Analyzed      GE, Mcal/kg  4.03  4.07  4.11      NE,7 Mcal/kg  2.15  2.26  2.37      DE,8 Mcal/kg  3.35  3.45  3.49      CP, %  28.99  26.74  24.70      Starch,9 %  30.31  34.84  38.62      Sugars,10 %  10.33  9.76  6.26      NSP,11 %  9.62  8.88  9.37      Crude fat, %  3.54  3.93  5.41      Crude fiber, %  2.99  2.56  2.35      Ash, %  7.25  6.83  6.30    Formulated NE concentration, Mcal/kg  Nutrient  2.21  2.32  2.42  Calculated      ME, Mcal/kg  3.26  3.32  3.37      DE, Mcal/kg  3.48  3.53  3.57      DM, %  89.42  89.51  89.63      CP,2 %  28.29  25.94  23.55      Crude fat, %  2.17  3.97  5.22      Crude fiber, %  2.68  2.58  2.48      Total Lys,2 %  1.63  1.65  1.67      TID Lys,3 %  1.47  1.51  1.55      TEAAN,4 %  1.90  1.76  1.62      TEAAN:TNEAAN5  0.72  0.74  0.76      dEB,6 mEq/kg  303  254  238  Analyzed      GE, Mcal/kg  4.03  4.07  4.11      NE,7 Mcal/kg  2.15  2.26  2.37      DE,8 Mcal/kg  3.35  3.45  3.49      CP, %  28.99  26.74  24.70      Starch,9 %  30.31  34.84  38.62      Sugars,10 %  10.33  9.76  6.26      NSP,11 %  9.62  8.88  9.37      Crude fat, %  3.54  3.93  5.41      Crude fiber, %  2.99  2.56  2.35      Ash, %  7.25  6.83  6.30  1 Calculated DE and ME concentrations were based on NRC (1998) values of each ingredient; calculated NE concentrations were based on NE value of ingredients (Centraal Veevoederbureau, 1998). 2 Calculated levels were based on the preassayed CP or total Lys content of soybean meal, fish meal, and skim milk; other ingredients were based on the NRC (1998) total Lys content. 3 TID = true ileal digestible; calculated based on the analyzed AA content and TID value (NRC, 1998) of individual ingredients. 4 TEAAN = total essential AA nitrogen. 5 TNEAAN = total nonessential AA nitrogen. 6 dEB = dietary electrolyte balance, Na + K − Cl (Patience et al., 1987). 7 Estimated from analyzed digestible nutrient contents according to the Centraal Veevoederbureau (1994) equation. 8 Calculated based on apparent digestibility values of GE. 9 Determined enzymatically (AOAC, 2002). 10 Sugars were calculated as total carbohydrates (starch + total NSP). 11 NSP = nonstarch polysaccharides. View Large Table 2. Calculated and analyzed nutrient content of the experimental diets, as-fed basis1   Formulated NE concentration, Mcal/kg  Nutrient  2.21  2.32  2.42  Calculated      ME, Mcal/kg  3.26  3.32  3.37      DE, Mcal/kg  3.48  3.53  3.57      DM, %  89.42  89.51  89.63      CP,2 %  28.29  25.94  23.55      Crude fat, %  2.17  3.97  5.22      Crude fiber, %  2.68  2.58  2.48      Total Lys,2 %  1.63  1.65  1.67      TID Lys,3 %  1.47  1.51  1.55      TEAAN,4 %  1.90  1.76  1.62      TEAAN:TNEAAN5  0.72  0.74  0.76      dEB,6 mEq/kg  303  254  238  Analyzed      GE, Mcal/kg  4.03  4.07  4.11      NE,7 Mcal/kg  2.15  2.26  2.37      DE,8 Mcal/kg  3.35  3.45  3.49      CP, %  28.99  26.74  24.70      Starch,9 %  30.31  34.84  38.62      Sugars,10 %  10.33  9.76  6.26      NSP,11 %  9.62  8.88  9.37      Crude fat, %  3.54  3.93  5.41      Crude fiber, %  2.99  2.56  2.35      Ash, %  7.25  6.83  6.30    Formulated NE concentration, Mcal/kg  Nutrient  2.21  2.32  2.42  Calculated      ME, Mcal/kg  3.26  3.32  3.37      DE, Mcal/kg  3.48  3.53  3.57      DM, %  89.42  89.51  89.63      CP,2 %  28.29  25.94  23.55      Crude fat, %  2.17  3.97  5.22      Crude fiber, %  2.68  2.58  2.48      Total Lys,2 %  1.63  1.65  1.67      TID Lys,3 %  1.47  1.51  1.55      TEAAN,4 %  1.90  1.76  1.62      TEAAN:TNEAAN5  0.72  0.74  0.76      dEB,6 mEq/kg  303  254  238  Analyzed      GE, Mcal/kg  4.03  4.07  4.11      NE,7 Mcal/kg  2.15  2.26  2.37      DE,8 Mcal/kg  3.35  3.45  3.49      CP, %  28.99  26.74  24.70      Starch,9 %  30.31  34.84  38.62      Sugars,10 %  10.33  9.76  6.26      NSP,11 %  9.62  8.88  9.37      Crude fat, %  3.54  3.93  5.41      Crude fiber, %  2.99  2.56  2.35      Ash, %  7.25  6.83  6.30  1 Calculated DE and ME concentrations were based on NRC (1998) values of each ingredient; calculated NE concentrations were based on NE value of ingredients (Centraal Veevoederbureau, 1998). 2 Calculated levels were based on the preassayed CP or total Lys content of soybean meal, fish meal, and skim milk; other ingredients were based on the NRC (1998) total Lys content. 3 TID = true ileal digestible; calculated based on the analyzed AA content and TID value (NRC, 1998) of individual ingredients. 4 TEAAN = total essential AA nitrogen. 5 TNEAAN = total nonessential AA nitrogen. 6 dEB = dietary electrolyte balance, Na + K − Cl (Patience et al., 1987). 7 Estimated from analyzed digestible nutrient contents according to the Centraal Veevoederbureau (1994) equation. 8 Calculated based on apparent digestibility values of GE. 9 Determined enzymatically (AOAC, 2002). 10 Sugars were calculated as total carbohydrates (starch + total NSP). 11 NSP = nonstarch polysaccharides. View Large The AA profile of each diet was adjusted based on true ileal digestible (TID) AA profiles (NRC, 1998), such that the TID Lys/Mcal of DE ratio exceeded the requirement for this class of pig (Oresanya et al., 2007). Other AA were formulated to levels according to the ideal protein ratio for this BW class of pig (NRC, 1998). This ensured that the AA supply was nonlimiting for growth. Diet formulation was based on the assayed CP and AA composition of soybean meal, fish meal, and skim milk powder (Degussa Corporation, Amino Acid Laboratory, Allendale, NJ). Data and Sample Collection Pigs were weighed at the initiation of feeding of the experimental diets (31.5 ± 0.3 d of age and 9.5 ± 1.0 kg of BW) and twice weekly thereafter on Mondays and Thursdays before feeding. Feed disappearance was measured at each weigh day for the pigs fed on an ad libitum basis, and the daily feed allowances for the limit-fed pigs were adjusted based on the ad libitum access intake on each diet, calculated on a BW basis. Freshly voided feces were collected from each pig by using the grab method (Veum et al., 2004) over 3 d (d 15 to 17) and pooled per pig, to determine DE and to estimate NE concentration of diets from the digestible nutrient content. Fecal samples were frozen and stored at −20°C until they were lyophilized with a freeze-drier (Model 40-SUB, Virtis Co. Ltd., Gardiner, NY). Feed samples were taken at the time of feeding and pooled per diet. All samples were stored at −20°C until required for analysis. A blood sample from each pig was taken at approximately 1100 on d 7 and again on d 21. Blood samples were collected via venipuncture into Vacutainer tubes containing 143 USP units of sodium heparin (Becton, Dickinson and Co., Oakville, Ontario, Canada). Plasma was harvested after centrifugation at 700 × g for 15 min (Model Centrific 228, Fisher, Nepean, Ontario, Canada) and stored at −20°C for later assay of IGF-I concentration. Plasma samples were analyzed for IGF-I by RIA as described previously (Kerr et al., 1990) after acid-ethanol extraction (Daughaday et al., 1980). Slaughter Procedure and Carcass Measurement The comparative slaughter procedure was applied to replicates 1 and 2. Replicate 3 was conducted to increase the number of pigs for the growth performance study only. Pigs assigned to the ISG were killed at the commencement of the experiment (d 0). The rest of the pigs remained on the experimental treatments until they reached 25 ± 1 kg of BW, at which time they were killed to determine body composition. Pigs were euthanized by CO2 asphyxiation followed by exsanguination (Hoenderken, 1983; Gregory et al., 1987). The carcass was split down the ventral midline from the groin to the chest cavity, and the entire viscera were removed from the carcass. The bladder was aspirated of its contents by using a syringe and was left attached to the carcass. The gastrointestinal tract was separated from the viscera and weighed, emptied of all digesta, patted dry, and reweighed. The liver, kidneys, heart, lungs, and spleen were weighed individually. All individual weights included the associated fat (i.e., mesenteric, renal, and pericardial fat). The weights of the organ fraction and blood were recorded as total organ weight and are referred to herein as “noncarcass.” The weight of the eviscerated carcass (including head and feet) was recorded and is referred to as “carcass.” The empty BW (EBW) of the pig was taken as the sum of the weight of the carcass and the noncarcass. The noncarcass fraction and blood were pooled and stored separately from the carcass. The carcass and noncarcass were frozen at −20°C until further processing. The frozen carcasses were cut into quartiles and passed through a 10-mm die 4 times in a commercial grinder (Model 801 GHP-25, Autio Company, Astoria, OR). After the final pass through the grinder, subsamples of the carcass were collected and manually blended to produce a 250-g sample, which was then placed in a previously weighed aluminum container for later analysis. The noncarcass fraction was passed through the die once and mixed thoroughly before several subsamples were placed in a previously weighed aluminum container. All samples were weighed immediately after collection and kept frozen until freeze-drying to a constant weight. Chemical Analyses Feed and lyophilized fecal samples were prepared for chemical analyses by air-equilibration and passed through a 1-mm screen (Retsch Model ZM1, Brinkman Instrument of Canada Ltd., Rexdale, Ontario, Canada). The acid insoluble ash content of the diet was used as an indigestible marker and was measured in feed and feces (McCarthy et al., 1974) to determine the apparent total tract digestibility of DM and other nutrients. Pure celite standard samples were assayed to confirm the accuracy of the analytical procedure, and a recovery of 99.9 ± 0.01% was attained. The moisture contents of feed and freeze-dried fecal samples were determined by drying at 135°C in an airflow-type oven for 2 h (method 930.15; AOAC, 1990). Nitrogen in feed and fecal samples was measured by combustion (method 968.06; AOAC, 1990) with a Leco protein/nitrogen apparatus (Model FP-528, Leco Corp., St. Joseph, MI). Calibration was conducted with an EDTA standard (nitrogen concentration 9.57 ± 0.02%; Leco Corp.). On analysis, the nitrogen concentration of EDTA was 9.56 ± 0.02%. Crude protein was calculated as nitrogen × 6.25. Gross energy was measured in an adiabatic bomb calorimeter (Model 1281, Parr Instruments, Moline, IL). Benzoic acid (6,318 kcal/kg; Parr Instruments) was used as the standard for calibration and was determined to be 6,317 ± 2 kcal/kg at assay. Crude fat in feed samples was determined after ether extraction (method 920.39; AOAC, 1990) in an extractor apparatus (Labconco Corp., Kansas City, MO) and in fecal samples after acidification with 9 N HCl to allow quantification of saponified fatty acids, followed by ether extraction. Feed and fecal samples were analyzed for crude fiber by using an Ankom fiber analyzer (Ankom Technology Co., Fairport, MI). Ash was determined by incineration in a muffle furnace at 600°C for 12 h. Feed samples were passed through a 0.5-mm screen and analyzed enzymatically for starch (method 996.11; AOAC, 2002) by using a total starch assay kit (AA/ AMG, Megazyme International Ireland Ltd., Bray, Co. Wicklow, Ireland). Feed samples were analyzed for total carbohydrates, total nonstarch polysaccharides, and free sugars based on the methods of Englyst and Hudson (1987) and Englyst (1989), respectively. Total sugars were calculated as total carbohydrates (starch + total nonstarch polysaccharides). According to Graham et al. (1986) and Bach Knudsen and Hansen (1991), apparent total tract digestibility of starch and sugar were assumed to be 100%; therefore, starch and sugar were not determined in the fecal samples. Freeze-dried carcass and noncarcass samples were prepared for chemical analyses by blending in a grinder (Retsch Grindomix, Model GM200, F. Kurt Retsch GmbH and Co. KG, Haan, Germany). Samples were analyzed for DM, GE, crude fat, and ash as described above. Nitrogen was measured with the Leco apparatus (method 992.15; AOAC, 2002) and CP was expressed as nitrogen × 6.25. All chemical analyses were carried out in duplicate and were repeated when the intraassay CV exceeded 3%. Calculations and Statistical Analyses Apparent digestibility values of N, energy, and other nutrients were determined by using the following equation:  \[D_{ADN}\%\ =\ 100\%\ {-}\ [(I_{D}\ {\times}\ A_{F})/(A_{D}\ {\times}\ I_{F})\ {\times}\ 100],\] where DADN is the apparent digestibility value of a nutrient N, ID is the percentage index marker concentration in the assay diet, AF is the percentage nutrient concentration in feces, AD is the percentage nutrient concentration in the assay diet, and IF is the percentage index marker concentration in feces, all on a DM basis. The equation given by Noblet and Perez (1993) was used to calculate ME, and NE was estimated from digestible nutrients according to Centraal Veevoederbureau (1994):  \[ME\ =\ 0.999\ {\times}\ [DE\ {-}\ (0.82\ {\times}\ DCP)],\] and  \begin{eqnarray*}&&NE\ =\ (2.58\ {\times}\ DCP)\ +\ (8.63\ {\times}\ DEE)\ +\ (3.23\ {\times}\ ST)\\&&+\ (3.04\ {\times}\ SG)\ +\ (2.27\ {\times}\ DRES),\end{eqnarray*} where NE is expressed in kilocalories per kilogram (as-is), DCP is digestible CP, DEE is digestible ether extract, ST is starch, SG is sugar, and DRES is digestible residuals, calculated as digestible OM − (DCP + DEE + ST + SG + digestible crude fiber). Digestible energy intake was calculated from the measured DE concentration × ADFI. Similarly, ME intake (MEi) was quantified from the calculated ME concentration × ADFI, and NEi was quantified from the calculated NE concentration × ADFI. Digestible energy intake for maintenance (DEim) was calculated as 0.110 Mcal/(kg of BW0.75 × d) (NRC, 1998) and NE for maintenance (NEim) was calculated as 0.078 Mcal/(kg of BW0.75 × d) (Just, 1982). Digestible energy and NE available for growth (DEig and NEig, respectively) were calculated as DEi − DEim or NEi − NEim. Energy efficiency for gain (expressed as Mcal/kg) was calculated as DEig/ADG or NEig/ADG, where DEig or NEig was expressed in megacalories per day and ADG was the ADG in kilograms. Energy partitioning into protein and lipid deposition (expressed as g/Mcal) was calculated as protein deposition (PD) [or lipid deposition (LD)]/DEig or PD (or LD)/NEig, where PD and LD were the respective determined deposition rates (g/d) of the slaughtered experimental pigs, calculated as described below. The relationship between live BW and EBW at slaughter was determined for the ISG. This was used together with the data from chemical analysis of the carcass and noncarcass of the ISG to estimate the initial body composition of the experimental pigs. The gains in protein, lipid, ash, water, and energy were estimated as  \begin{eqnarray*}&&[(Final\ content,\ g\ or\ Mcal)\\&&{-}\ (initial\ content,\ g\ or\ Mcal)]/number\ of\ d\ on\ trial.\end{eqnarray*} Empty body GE content was estimated in 2 ways, by bomb calorimeter analysis conducted on carcass and noncarcass and by calculation based on the analyzed protein and lipid concentrations and using the factors 5.66 and 9.46 Mcal/kg for protein and lipids, respectively (Ewan, 2001). Similarly, energy retained as protein (ERP) and energy retained as lipids (ERL) were calculated as PD (in g/d) × 5.66 kcal/g and LD (in g/d) × 9.46 kcal/g, respectively. Statistical Analyses. Data were analyzed by using the MIXED procedure (SAS Inst. Inc., Cary, NC) with the individual pig as the experimental unit and initial BW as a covariate for performance data. The statistical model included the effect of diet, feeding level, and the diet × feeding level interaction. Plasma IGF-I concentration data were analyzed by using repeated measures and appropriate covariance structures (Littell et al., 1998; Wang and Goonewardene, 2004). The statistical model included the effect of day, diet, feeding level, and the following interactions: diet × day, and diet × feeding level. Regression analyses within SAS were used to evaluate the efficiency of utilization of measured DE and calculated NE within diets for growth and nutrient deposition. Differences in the slopes of the regression lines were evaluated according to the methods of Zar (1984). Pearson correlation coefficients between DEi, NEi and performance, and carcass variables were analyzed by using the correlation procedure of SAS. Least squares means are reported, and differences were considered significant at P < 0.05. Trends (0.05 < P < 0.10) are reported, and P > 0.10 was considered nonsignificant. RESULTS Performance Average daily gain, ADFI, and G:F were not affected by dietary NE concentration, but days on test was longest for pigs fed the intermediate dietary NE concentration (P < 0.05). Final BW, ADG, and ADFI increased (P < 0.05), whereas days on trial declined (P < 0.001; Table 3) with increasing feeding level. Dietary NE concentration and feeding level did not affect G:F. However, a NE × feeding level interaction (P = 0.031) on G:F was observed, because pigs fed the intermediate NE concentration diet at the 80% feeding level exhibited decreased G:F compared with the other treatments. Table 3. Effect of dietary NE concentration and feeding level on the performance of barrows from 9 to 25 kg1,2   NE,3 Mcal/kg  Feeding level,4 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          Initial BW, kg  9.47  9.49  9.44  9.53  9.46  9.40  0.12        Final BW, kg  24.76  24.98  24.92  24.63  24.85  25.17  0.17  0.555  0.045  0.657  Days on trial  27.1  28.4  27.3  31.0  29.0  22.8  0.6  0.033  <0.001  0.749  ADG, g  577  561  579  491  534  692  8  0.228  <0.001  0.342  ADFI, g  789  771  784  661  740  943  9  0.345  <0.001  0.148  G:F g/g  0.733  0.727  0.740  0.743  0.724  0.733  0.009  0.534  0.283  0.031    NE,3 Mcal/kg  Feeding level,4 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          Initial BW, kg  9.47  9.49  9.44  9.53  9.46  9.40  0.12        Final BW, kg  24.76  24.98  24.92  24.63  24.85  25.17  0.17  0.555  0.045  0.657  Days on trial  27.1  28.4  27.3  31.0  29.0  22.8  0.6  0.033  <0.001  0.749  ADG, g  577  561  579  491  534  692  8  0.228  <0.001  0.342  ADFI, g  789  771  784  661  740  943  9  0.345  <0.001  0.148  G:F g/g  0.733  0.727  0.740  0.743  0.724  0.733  0.009  0.534  0.283  0.031  1 Data are least squares means of 81 individually housed barrows (9 barrows per NE × feeding level). 2 Data were analyzed with initial BW as a covariate. The covariate was significant (P < 0.05) for final BW, days on trial, ADG, and ADFI, but not significant for G:F. 3 NE concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 4 In the 100% treatment group, pigs within a treatment were allowed unrestricted access to experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. View Large Table 3. Effect of dietary NE concentration and feeding level on the performance of barrows from 9 to 25 kg1,2   NE,3 Mcal/kg  Feeding level,4 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          Initial BW, kg  9.47  9.49  9.44  9.53  9.46  9.40  0.12        Final BW, kg  24.76  24.98  24.92  24.63  24.85  25.17  0.17  0.555  0.045  0.657  Days on trial  27.1  28.4  27.3  31.0  29.0  22.8  0.6  0.033  <0.001  0.749  ADG, g  577  561  579  491  534  692  8  0.228  <0.001  0.342  ADFI, g  789  771  784  661  740  943  9  0.345  <0.001  0.148  G:F g/g  0.733  0.727  0.740  0.743  0.724  0.733  0.009  0.534  0.283  0.031    NE,3 Mcal/kg  Feeding level,4 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          Initial BW, kg  9.47  9.49  9.44  9.53  9.46  9.40  0.12        Final BW, kg  24.76  24.98  24.92  24.63  24.85  25.17  0.17  0.555  0.045  0.657  Days on trial  27.1  28.4  27.3  31.0  29.0  22.8  0.6  0.033  <0.001  0.749  ADG, g  577  561  579  491  534  692  8  0.228  <0.001  0.342  ADFI, g  789  771  784  661  740  943  9  0.345  <0.001  0.148  G:F g/g  0.733  0.727  0.740  0.743  0.724  0.733  0.009  0.534  0.283  0.031  1 Data are least squares means of 81 individually housed barrows (9 barrows per NE × feeding level). 2 Data were analyzed with initial BW as a covariate. The covariate was significant (P < 0.05) for final BW, days on trial, ADG, and ADFI, but not significant for G:F. 3 NE concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 4 In the 100% treatment group, pigs within a treatment were allowed unrestricted access to experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. View Large Digestible energy intake and DEig were similar across dietary NE concentrations (Table 4). Net energy intake and NEig increased with increased dietary NE concentration (P < 0.001). As expected, DEi, DEig, NEi, and NEig increased with increasing feeding level (P < 0.001). Table 4. Effect of dietary NE concentration and feeding level on energy utilization in barrows from 9 to 25 kg1   NE,2 Mcal/kg  Feeding level,3%    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          DE intake,4 Mcal/d  3.22  3.23  3.32  2.83  3.11  3.83  0.04  0.220  <0.001  0.622  Maintenance4 (DEim)  0.92  0.93  0.93  0.92  0.93  0.93  0.01  0.845  0.716  0.676  Growth4 (DEig)  2.29  2.30  2.39  1.90  2.18  2.90  0.04  0.165  <0.001  0.553  DEi utilization  Mcal of DE/kg of wt gain5  3.96  4.11  4.12  3.88  4.10  4.21  0.06  0.113  <0.001  0.179  g of protein/Mcal of DE5  41.7  40.2  39.4  42.5  40.3  38.4  0.6  0.052  <0.001  0.220  g of lipid/Mcal of DE5  15.4  17.4  21.3  16.9  16.5  20.7  0.8  <0.001  <0.001  0.004  NE intake,6 Mcal/d  2.07  2.12  2.26  1.86  2.04  2.54  0.03  <0.001  <0.001  0.469  Maintenance6 (NEim)  0.66  0.66  0.66  0.66  0.66  0.66  0.01  0.860  0.728  0.678  Growth6 (NEig)  1.41  1.46  1.60  1.20  1.39  1.88  0.03  <0.001  <0.001  0.368  DEi utilization  Mcal of NE/kg of wt gain7  2.43  2.59  2.75  2.44  2.60  2.73  0.04  0.001  0.001  0.136  g of protein/Mcal of NE7  68.0  63.9  59.4  68.0  63.9  59.3  1.0  0.001  0.001  0.239  g of lipid/Mcal of NE7  25.0  27.7  32.2  27.2  26.0  31.7  1.3  0.001  0.008  0.004    NE,2 Mcal/kg  Feeding level,3%    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          DE intake,4 Mcal/d  3.22  3.23  3.32  2.83  3.11  3.83  0.04  0.220  <0.001  0.622  Maintenance4 (DEim)  0.92  0.93  0.93  0.92  0.93  0.93  0.01  0.845  0.716  0.676  Growth4 (DEig)  2.29  2.30  2.39  1.90  2.18  2.90  0.04  0.165  <0.001  0.553  DEi utilization  Mcal of DE/kg of wt gain5  3.96  4.11  4.12  3.88  4.10  4.21  0.06  0.113  <0.001  0.179  g of protein/Mcal of DE5  41.7  40.2  39.4  42.5  40.3  38.4  0.6  0.052  <0.001  0.220  g of lipid/Mcal of DE5  15.4  17.4  21.3  16.9  16.5  20.7  0.8  <0.001  <0.001  0.004  NE intake,6 Mcal/d  2.07  2.12  2.26  1.86  2.04  2.54  0.03  <0.001  <0.001  0.469  Maintenance6 (NEim)  0.66  0.66  0.66  0.66  0.66  0.66  0.01  0.860  0.728  0.678  Growth6 (NEig)  1.41  1.46  1.60  1.20  1.39  1.88  0.03  <0.001  <0.001  0.368  DEi utilization  Mcal of NE/kg of wt gain7  2.43  2.59  2.75  2.44  2.60  2.73  0.04  0.001  0.001  0.136  g of protein/Mcal of NE7  68.0  63.9  59.4  68.0  63.9  59.3  1.0  0.001  0.001  0.239  g of lipid/Mcal of NE7  25.0  27.7  32.2  27.2  26.0  31.7  1.3  0.001  0.008  0.004  1 Except when indicated, data are presented as least squares means of 81 individually housed barrows (9 barrows per NE × feeding level combination). 2 NE concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 3 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 4 DE intake was calculated from measured DE and ADFI. Net energy intake was calculated from NE concentration as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). Digestible energy available for maintenance was calculated as 0.110 Mcal/(kg of BW0.75 × d). Digestible energy available for growth was calculated as DE intake − DEim. 5 Calculated as DEig/ADG; g of protein/Mcal of DE and g of lipid/Mcal of DE were calculated from the observed protein and lipid deposition of killed pigs (n = 54 pigs; 6 pigs per dietary NE concentration × feeding level combination). 6 Net energy intake was calculated from NE concentration as estimated from digestible nutrients (Centraal Veevoederbureau, 1994) and ADFI. Net energy for maintenance was calculated as 0.078 Mcal/(kg of BW0.75 × d). Net energy for growth was calculated as NE intake −NEim. 7 Calculated as NEig/ADG; g of protein/Mcal of NE and g of lipid/Mcal of NE were calculated from the observed protein and lipid deposition of killed pigs (n = 54 pigs; 6 pigs per dietary NE concentration × feeding level combination). View Large Table 4. Effect of dietary NE concentration and feeding level on energy utilization in barrows from 9 to 25 kg1   NE,2 Mcal/kg  Feeding level,3%    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          DE intake,4 Mcal/d  3.22  3.23  3.32  2.83  3.11  3.83  0.04  0.220  <0.001  0.622  Maintenance4 (DEim)  0.92  0.93  0.93  0.92  0.93  0.93  0.01  0.845  0.716  0.676  Growth4 (DEig)  2.29  2.30  2.39  1.90  2.18  2.90  0.04  0.165  <0.001  0.553  DEi utilization  Mcal of DE/kg of wt gain5  3.96  4.11  4.12  3.88  4.10  4.21  0.06  0.113  <0.001  0.179  g of protein/Mcal of DE5  41.7  40.2  39.4  42.5  40.3  38.4  0.6  0.052  <0.001  0.220  g of lipid/Mcal of DE5  15.4  17.4  21.3  16.9  16.5  20.7  0.8  <0.001  <0.001  0.004  NE intake,6 Mcal/d  2.07  2.12  2.26  1.86  2.04  2.54  0.03  <0.001  <0.001  0.469  Maintenance6 (NEim)  0.66  0.66  0.66  0.66  0.66  0.66  0.01  0.860  0.728  0.678  Growth6 (NEig)  1.41  1.46  1.60  1.20  1.39  1.88  0.03  <0.001  <0.001  0.368  DEi utilization  Mcal of NE/kg of wt gain7  2.43  2.59  2.75  2.44  2.60  2.73  0.04  0.001  0.001  0.136  g of protein/Mcal of NE7  68.0  63.9  59.4  68.0  63.9  59.3  1.0  0.001  0.001  0.239  g of lipid/Mcal of NE7  25.0  27.7  32.2  27.2  26.0  31.7  1.3  0.001  0.008  0.004    NE,2 Mcal/kg  Feeding level,3%    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          DE intake,4 Mcal/d  3.22  3.23  3.32  2.83  3.11  3.83  0.04  0.220  <0.001  0.622  Maintenance4 (DEim)  0.92  0.93  0.93  0.92  0.93  0.93  0.01  0.845  0.716  0.676  Growth4 (DEig)  2.29  2.30  2.39  1.90  2.18  2.90  0.04  0.165  <0.001  0.553  DEi utilization  Mcal of DE/kg of wt gain5  3.96  4.11  4.12  3.88  4.10  4.21  0.06  0.113  <0.001  0.179  g of protein/Mcal of DE5  41.7  40.2  39.4  42.5  40.3  38.4  0.6  0.052  <0.001  0.220  g of lipid/Mcal of DE5  15.4  17.4  21.3  16.9  16.5  20.7  0.8  <0.001  <0.001  0.004  NE intake,6 Mcal/d  2.07  2.12  2.26  1.86  2.04  2.54  0.03  <0.001  <0.001  0.469  Maintenance6 (NEim)  0.66  0.66  0.66  0.66  0.66  0.66  0.01  0.860  0.728  0.678  Growth6 (NEig)  1.41  1.46  1.60  1.20  1.39  1.88  0.03  <0.001  <0.001  0.368  DEi utilization  Mcal of NE/kg of wt gain7  2.43  2.59  2.75  2.44  2.60  2.73  0.04  0.001  0.001  0.136  g of protein/Mcal of NE7  68.0  63.9  59.4  68.0  63.9  59.3  1.0  0.001  0.001  0.239  g of lipid/Mcal of NE7  25.0  27.7  32.2  27.2  26.0  31.7  1.3  0.001  0.008  0.004  1 Except when indicated, data are presented as least squares means of 81 individually housed barrows (9 barrows per NE × feeding level combination). 2 NE concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 3 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 4 DE intake was calculated from measured DE and ADFI. Net energy intake was calculated from NE concentration as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). Digestible energy available for maintenance was calculated as 0.110 Mcal/(kg of BW0.75 × d). Digestible energy available for growth was calculated as DE intake − DEim. 5 Calculated as DEig/ADG; g of protein/Mcal of DE and g of lipid/Mcal of DE were calculated from the observed protein and lipid deposition of killed pigs (n = 54 pigs; 6 pigs per dietary NE concentration × feeding level combination). 6 Net energy intake was calculated from NE concentration as estimated from digestible nutrients (Centraal Veevoederbureau, 1994) and ADFI. Net energy for maintenance was calculated as 0.078 Mcal/(kg of BW0.75 × d). Net energy for growth was calculated as NE intake −NEim. 7 Calculated as NEig/ADG; g of protein/Mcal of NE and g of lipid/Mcal of NE were calculated from the observed protein and lipid deposition of killed pigs (n = 54 pigs; 6 pigs per dietary NE concentration × feeding level combination). View Large The efficiency of energy utilization for growth (Mcal of NE/kg) declined with increased dietary NE concentration and feeding level (P < 0.001; Table 4). The partition of DEig and NEig to PD (g/Mcal) tended to decline (P = 0.052) and declined (P < 0.001), respectively, as dietary NE concentration increased. In contrast, the partitions of DEig and NEig to LD (g/Mcal) were increased with increased dietary NE concentration and feeding level (P < 0.05). However, a NE × feeding level interaction (P < 0.05) was observed because of a greater lipid deposition per megacalorie of DEig and NEig in pigs allowed ad libitum access to the high-NE concentration diet compared with those receiving other treatments (P < 0.05). Regression analyses within dietary NE concentration showed differences in the slope of the linear relationship between ADG and NEig (P < 0.05; Figure 1). Similar analyses revealed differences in the slope (P < 0.05) of the linear relationship between PD, LD, and the LD:PD ratio and NEig (Figure 1). Figure 1. View largeDownload slide Relationship of NE intake available for growth (NEig) and (A) ADG; (B) protein deposition (PD); (C) lipid deposition (LD); and (D) lipid:protein ratio in barrows from 9 to 25 kg fed diets with increasing NE concentration (2.21, 2.26, and 2.37 Mcal of NE/kg, as-fed basis) at 3 feeding levels (100, 80, or 70% of ad libitum feed intake). (A) Linear regression equations: (2.15, Mcal/kg): ADG = 177 + 283NEig, R2 0.87; (2.26, Mcal/kg): ADG = 124 + 300NEig, R2 0.79; (2.37, Mcal/kg): ADG = 156 + 264NEig, R2 0.89; the slopes differed (P < 0.001). (B) Linear regression equations: (2.15, Mcal/kg): PD = 40 + 38NEig, R2 0.81; (2.26, Mcal/kg): PD = 306 + 42NEig, R2 0.77; (2.37, Mcal/kg): PD = 28 + 41NEig, R2 0.97; the slopes differed (P < 0.002). (C) Linear regression equations: (2.15, Mcal/kg): LD = −4.00 + 30.0NEig, R2 0.55; (2.26, Mcal/kg): LD = 0.28 + 27.5NEig, R2 0.53; (2.37, Mcal/kg): LD = −50.33 + 65.0NEig, R2 0.92; the slopes differed (P < 0.001). (D) Linear regression equations: (2.15, Mcal/kg): LD:PD ratio = 0.20 + 0.18NEig, R2 0.21; (2.26, Mcal/kg): LD:PD ratio = 0.32 + 0.11NEig, R2 0.10; (2.37, Mcal/kg): LD:PD ratio = −0.04 + 0.49NEig, R2 0.78; the slopes differed (P < 0.003). Figure 1. View largeDownload slide Relationship of NE intake available for growth (NEig) and (A) ADG; (B) protein deposition (PD); (C) lipid deposition (LD); and (D) lipid:protein ratio in barrows from 9 to 25 kg fed diets with increasing NE concentration (2.21, 2.26, and 2.37 Mcal of NE/kg, as-fed basis) at 3 feeding levels (100, 80, or 70% of ad libitum feed intake). (A) Linear regression equations: (2.15, Mcal/kg): ADG = 177 + 283NEig, R2 0.87; (2.26, Mcal/kg): ADG = 124 + 300NEig, R2 0.79; (2.37, Mcal/kg): ADG = 156 + 264NEig, R2 0.89; the slopes differed (P < 0.001). (B) Linear regression equations: (2.15, Mcal/kg): PD = 40 + 38NEig, R2 0.81; (2.26, Mcal/kg): PD = 306 + 42NEig, R2 0.77; (2.37, Mcal/kg): PD = 28 + 41NEig, R2 0.97; the slopes differed (P < 0.002). (C) Linear regression equations: (2.15, Mcal/kg): LD = −4.00 + 30.0NEig, R2 0.55; (2.26, Mcal/kg): LD = 0.28 + 27.5NEig, R2 0.53; (2.37, Mcal/kg): LD = −50.33 + 65.0NEig, R2 0.92; the slopes differed (P < 0.001). (D) Linear regression equations: (2.15, Mcal/kg): LD:PD ratio = 0.20 + 0.18NEig, R2 0.21; (2.26, Mcal/kg): LD:PD ratio = 0.32 + 0.11NEig, R2 0.10; (2.37, Mcal/kg): LD:PD ratio = −0.04 + 0.49NEig, R2 0.78; the slopes differed (P < 0.003). Regression analyses were conducted to relate PD, LD, and the LD:PD ratio to DEi or to NEi. These relationships were described by equations that included a significant quadratic (P < 0.001) term of energy intake (Table 5). Carrying this one step further, total retained energy (RE), ERP, and ERL were correlated with DEi by using DEi (kcal/kg of BW0.75 per d) as the independent variable and RE, ERP, and ERL (kcal/kg of BW0.75 per d) as dependent variables. By setting RE = 0, the quantity of DE required for maintenance (DEim) was estimated at 118 kcal/kg of BW0.75 per d. In the same manner, the ME required for maintenance (MEim) was estimated to be 116 kcal/kg of BW0.75 per d and the NE required for maintenance (NEim, the MEi at zero RE) was estimated to be 71 kcal/kg of BW0.75 per d. Table 5. Protein, lipid, and lipid:protein deposition ratio as a function of energy intake in barrows fed diets with increasing NE concentration at 3 feeding levels1,2,3,4 No.  Equation  R2  RMSE5  1  PD = −47.79 + 58.70DEi − 4.65DEi2  0.87  5.26  2  LD = 143.52 − 89.30DEi + 17.58DEi2  0.71  10.61  3  LD:PD ratio = 1.39 − 0.73DEi + 0.13DEi2  0.42  0.11  4  PD = −31.65 + 77.42NEi − 8.78NEi2  0.83  5.95  5  LD = 114.92 − 108.25NEi + 34.04NEi2  0.78  9.09  6  LD:PD ratio = 1.14 − 0.88NEi + 0.25NEi2  0.51  0.10  No.  Equation  R2  RMSE5  1  PD = −47.79 + 58.70DEi − 4.65DEi2  0.87  5.26  2  LD = 143.52 − 89.30DEi + 17.58DEi2  0.71  10.61  3  LD:PD ratio = 1.39 − 0.73DEi + 0.13DEi2  0.42  0.11  4  PD = −31.65 + 77.42NEi − 8.78NEi2  0.83  5.95  5  LD = 114.92 − 108.25NEi + 34.04NEi2  0.78  9.09  6  LD:PD ratio = 1.14 − 0.88NEi + 0.25NEi2  0.51  0.10  1 PD = protein deposition; LD = lipid deposition; LD:PD = protein:lipid ratio; DEi = DE intake; and NEi = NE intake. 2 PD and LD were expressed in g/d, and DEi and NEi were expressed in Mcal/d. 3 Energy intake (DEi and NEi, Mcal/d) was calculated from measured dietary DE concentration (or calculated NE concentration) as fed × ADFI. 4 n = 54; P < 0.001 for all equations. 5 Residual mean square error. View Large Table 5. Protein, lipid, and lipid:protein deposition ratio as a function of energy intake in barrows fed diets with increasing NE concentration at 3 feeding levels1,2,3,4 No.  Equation  R2  RMSE5  1  PD = −47.79 + 58.70DEi − 4.65DEi2  0.87  5.26  2  LD = 143.52 − 89.30DEi + 17.58DEi2  0.71  10.61  3  LD:PD ratio = 1.39 − 0.73DEi + 0.13DEi2  0.42  0.11  4  PD = −31.65 + 77.42NEi − 8.78NEi2  0.83  5.95  5  LD = 114.92 − 108.25NEi + 34.04NEi2  0.78  9.09  6  LD:PD ratio = 1.14 − 0.88NEi + 0.25NEi2  0.51  0.10  No.  Equation  R2  RMSE5  1  PD = −47.79 + 58.70DEi − 4.65DEi2  0.87  5.26  2  LD = 143.52 − 89.30DEi + 17.58DEi2  0.71  10.61  3  LD:PD ratio = 1.39 − 0.73DEi + 0.13DEi2  0.42  0.11  4  PD = −31.65 + 77.42NEi − 8.78NEi2  0.83  5.95  5  LD = 114.92 − 108.25NEi + 34.04NEi2  0.78  9.09  6  LD:PD ratio = 1.14 − 0.88NEi + 0.25NEi2  0.51  0.10  1 PD = protein deposition; LD = lipid deposition; LD:PD = protein:lipid ratio; DEi = DE intake; and NEi = NE intake. 2 PD and LD were expressed in g/d, and DEi and NEi were expressed in Mcal/d. 3 Energy intake (DEi and NEi, Mcal/d) was calculated from measured dietary DE concentration (or calculated NE concentration) as fed × ADFI. 4 n = 54; P < 0.001 for all equations. 5 Residual mean square error. View Large Apparent Digestibility Apparent digestibility of GE, DM, crude fat, and ash were increased (P < 0.001; Table 6) and CP was increased (P < 0.05) with increased dietary NE concentration. Apparent GE and DM digestibility increased up to 2%, whereas CP, ash, and crude fat digestibility were increased up to 1, 7, and 34%, respectively, with increased dietary NE concentration. Conversely, apparent crude fiber digestibility decreased (P < 0.001) by as much as 23% with increased dietary NE concentration. Table 6. Effect of dietary NE concentration and feeding level on apparent digestibility of energy, OM, and ash and on measured energy content of diets in barrows1   NE,2 Mcal/kg  Feeding level,3 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          GE, %  83.2  84.8  84.9  86.0  84.8  82.1  0.3  <0.001  <0.001  0.441  DM, %  83.9  85.4  85.6  86.5  85.4  83.0  0.2  <0.001  <0.001  0.519  CP, %  83.8  85.0  84.8  86.6  85.1  82.0  0.3  <0.036  <0.001  0.259  Crude fat, %  51.2  57.3  68.5  62.9  58.8  55.3  1.4  <0.001  <0.001  0.297  Crude fiber, %  45.2  40.8  35.0  44.5  42.6  33.9  2.4  <0.001  <0.001  0.879  Ash, %  60.3  63.5  64.5  65.0  63.0  60.4  0.4  <0.001  <0.001  0.290  DE,4 Mcal/kg  3.35  3.45  3.49  3.50  3.45  3.34  0.01  <0.001  <0.001  0.423  NE,5 Mcal/kg  2.15  2.26  2.37  2.30  2.27  2.21  0.01  <0.001  <0.001  0.248  NE:DE, %  64.2  65.4  67.9  65.6  65.7  66.3  0.1  <0.001  <0.001  0.212  NE:GE  53.5  55.5  57.7  56.5  55.7  54.4  0.1  <0.001  <0.001  0.345    NE,2 Mcal/kg  Feeding level,3 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          GE, %  83.2  84.8  84.9  86.0  84.8  82.1  0.3  <0.001  <0.001  0.441  DM, %  83.9  85.4  85.6  86.5  85.4  83.0  0.2  <0.001  <0.001  0.519  CP, %  83.8  85.0  84.8  86.6  85.1  82.0  0.3  <0.036  <0.001  0.259  Crude fat, %  51.2  57.3  68.5  62.9  58.8  55.3  1.4  <0.001  <0.001  0.297  Crude fiber, %  45.2  40.8  35.0  44.5  42.6  33.9  2.4  <0.001  <0.001  0.879  Ash, %  60.3  63.5  64.5  65.0  63.0  60.4  0.4  <0.001  <0.001  0.290  DE,4 Mcal/kg  3.35  3.45  3.49  3.50  3.45  3.34  0.01  <0.001  <0.001  0.423  NE,5 Mcal/kg  2.15  2.26  2.37  2.30  2.27  2.21  0.01  <0.001  <0.001  0.248  NE:DE, %  64.2  65.4  67.9  65.6  65.7  66.3  0.1  <0.001  <0.001  0.212  NE:GE  53.5  55.5  57.7  56.5  55.7  54.4  0.1  <0.001  <0.001  0.345  1 Data are least squares means. The experiment included a total of 81 barrows (9 barrows per NE × feeding level combination). 2 Net energy concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 3 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 4 Measured DE concentration. 5 Estimated according to the Centraal Veevoederbureau (1994) equation. View Large Table 6. Effect of dietary NE concentration and feeding level on apparent digestibility of energy, OM, and ash and on measured energy content of diets in barrows1   NE,2 Mcal/kg  Feeding level,3 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          GE, %  83.2  84.8  84.9  86.0  84.8  82.1  0.3  <0.001  <0.001  0.441  DM, %  83.9  85.4  85.6  86.5  85.4  83.0  0.2  <0.001  <0.001  0.519  CP, %  83.8  85.0  84.8  86.6  85.1  82.0  0.3  <0.036  <0.001  0.259  Crude fat, %  51.2  57.3  68.5  62.9  58.8  55.3  1.4  <0.001  <0.001  0.297  Crude fiber, %  45.2  40.8  35.0  44.5  42.6  33.9  2.4  <0.001  <0.001  0.879  Ash, %  60.3  63.5  64.5  65.0  63.0  60.4  0.4  <0.001  <0.001  0.290  DE,4 Mcal/kg  3.35  3.45  3.49  3.50  3.45  3.34  0.01  <0.001  <0.001  0.423  NE,5 Mcal/kg  2.15  2.26  2.37  2.30  2.27  2.21  0.01  <0.001  <0.001  0.248  NE:DE, %  64.2  65.4  67.9  65.6  65.7  66.3  0.1  <0.001  <0.001  0.212  NE:GE  53.5  55.5  57.7  56.5  55.7  54.4  0.1  <0.001  <0.001  0.345    NE,2 Mcal/kg  Feeding level,3 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  27  27  27  27  27  27          GE, %  83.2  84.8  84.9  86.0  84.8  82.1  0.3  <0.001  <0.001  0.441  DM, %  83.9  85.4  85.6  86.5  85.4  83.0  0.2  <0.001  <0.001  0.519  CP, %  83.8  85.0  84.8  86.6  85.1  82.0  0.3  <0.036  <0.001  0.259  Crude fat, %  51.2  57.3  68.5  62.9  58.8  55.3  1.4  <0.001  <0.001  0.297  Crude fiber, %  45.2  40.8  35.0  44.5  42.6  33.9  2.4  <0.001  <0.001  0.879  Ash, %  60.3  63.5  64.5  65.0  63.0  60.4  0.4  <0.001  <0.001  0.290  DE,4 Mcal/kg  3.35  3.45  3.49  3.50  3.45  3.34  0.01  <0.001  <0.001  0.423  NE,5 Mcal/kg  2.15  2.26  2.37  2.30  2.27  2.21  0.01  <0.001  <0.001  0.248  NE:DE, %  64.2  65.4  67.9  65.6  65.7  66.3  0.1  <0.001  <0.001  0.212  NE:GE  53.5  55.5  57.7  56.5  55.7  54.4  0.1  <0.001  <0.001  0.345  1 Data are least squares means. The experiment included a total of 81 barrows (9 barrows per NE × feeding level combination). 2 Net energy concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 3 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 4 Measured DE concentration. 5 Estimated according to the Centraal Veevoederbureau (1994) equation. View Large The effect of feeding level on apparent digestibility was similar for GE, DM, CP, crude fat, crude fiber, and ash, declining with increasing feeding level (P < 0.001). No interaction between dietary NE concentration and feeding level was detected for any digestibility values. As expected, measured DE and NE concentrations increased from the low-NE to the high-NE diet, but declined with increasing feeding level (P < 0.001). The ratios of NE:DE and NE:GE increased with increased dietary NE concentration (P < 0.001). In addition, the NE:DE ratio increased with increasing feeding level, whereas the NE:GE ratio declined (P < 0.001). Body Chemical Composition Protein concentration in carcass and empty body declined up to 3% with increased dietary NE concentration (P < 0.05; Table 7). There was a tendency (P < 0.10) for protein concentration in carcass and empty body to decline with increasing feeding level. Table 7. Effect of dietary NE concentration and feeding level on carcass, noncarcass, and empty body chemical composition of barrows at 25 kg of BW1,2     NE,4 Mcal/kg  Feeding level,5%    P-value  Item  ISG3  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  6  18  18  18  18  18  18          Carcass  Water, g/kg  713  703  699  691  702  700  691  3  0.010  0.010  0.003  Protein, g/kg  160  176  173  170  174  174  170  2  0.003  0.080  0.967  Lipid, g/kg  91  83  90  104  86  87  104  3  <0.001  <0.001  0.002  Ash, g/kg  34.0  33.5  33.9  32.3  34.3  33.6  31.8  0.6  0.090  0.004  0.518  GE,6 Mcal/kg  1.72  1.74  1.78  1.90  1.75  1.77  1.91  0.02  <0.001  <0.001  0.007  Noncarcass  Water, g/kg  821  800  798  796  800  798  795  1  0.305  0.096  0.206  Protein, g/kg  142  159  159  161  159  160  159  1  0.526  0.621  0.619  Lipid, g/kg  20  23  24  25  23  23  26  1  0.186  0.073  0.468  Ash, g/kg  11.1  12.4  12.5  12.4  12.3  12.4  12.7  0.3  0.911  0.609  0.285  GE,6 Mcal/kg  1.01  1.13  1.15  1.17  1.14  1.15  1.17  0.01  0.106  0.103  0.161  Empty body  Water, g/kg  733  721  718  711  720  718  711  3  0.025  0.040  0.004  Protein, g/kg  156  173  170  168  171  172  168  2  0.012  0.074  0.918  Lipid, g/kg  77  72  78  89  74  76  89  2  <0.001  <0.001  0.003  Ash, g/kg  29.6  29.5  30.0  28.6  30.3  29.7  28.0  0.6  0.064  <0.001  0.482  GE,6 Mcal/kg  1.59  1.63  1.66  1.76  1.64  1.65  1.76  0.02  <0.001  <0.001  0.006  GE,7 Mcal/kg  1.62  1.66  1.70  1.79  1.67  1.69  1.79  0.02  0.002  0.003  0.006      NE,4 Mcal/kg  Feeding level,5%    P-value  Item  ISG3  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  6  18  18  18  18  18  18          Carcass  Water, g/kg  713  703  699  691  702  700  691  3  0.010  0.010  0.003  Protein, g/kg  160  176  173  170  174  174  170  2  0.003  0.080  0.967  Lipid, g/kg  91  83  90  104  86  87  104  3  <0.001  <0.001  0.002  Ash, g/kg  34.0  33.5  33.9  32.3  34.3  33.6  31.8  0.6  0.090  0.004  0.518  GE,6 Mcal/kg  1.72  1.74  1.78  1.90  1.75  1.77  1.91  0.02  <0.001  <0.001  0.007  Noncarcass  Water, g/kg  821  800  798  796  800  798  795  1  0.305  0.096  0.206  Protein, g/kg  142  159  159  161  159  160  159  1  0.526  0.621  0.619  Lipid, g/kg  20  23  24  25  23  23  26  1  0.186  0.073  0.468  Ash, g/kg  11.1  12.4  12.5  12.4  12.3  12.4  12.7  0.3  0.911  0.609  0.285  GE,6 Mcal/kg  1.01  1.13  1.15  1.17  1.14  1.15  1.17  0.01  0.106  0.103  0.161  Empty body  Water, g/kg  733  721  718  711  720  718  711  3  0.025  0.040  0.004  Protein, g/kg  156  173  170  168  171  172  168  2  0.012  0.074  0.918  Lipid, g/kg  77  72  78  89  74  76  89  2  <0.001  <0.001  0.003  Ash, g/kg  29.6  29.5  30.0  28.6  30.3  29.7  28.0  0.6  0.064  <0.001  0.482  GE,6 Mcal/kg  1.59  1.63  1.66  1.76  1.64  1.65  1.76  0.02  <0.001  <0.001  0.006  GE,7 Mcal/kg  1.62  1.66  1.70  1.79  1.67  1.69  1.79  0.02  0.002  0.003  0.006  1 Data are least squares means of 54 individually housed barrows (6 barrows per NE × feeding level combination). 2 Carcass is the eviscerated pig including the head and feet; noncarcass is the pooled individual organs including emptied gastrointestinal tract and blood; empty body is the sum of the carcass and noncarcass. 3 Data of the initial slaughter group (ISG; n = 6) were used to estimate the initial body composition of the experimental pigs and were not included in the statistical analysis. Body weight at slaughter was 9.4 ± 1.0 kg (mean ± SD). 4 Net enegy concentration of each diet across feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 5 In the 100% treatment group, pigs within treatment were allowed unrestricted access to experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 6 Bomb calorimeter analysis. 7 Calculated from analyzed protein and lipid content by using 5.66 and 9.46 kcal/g for protein and lipids, respectively (Ewan, 2001). View Large Table 7. Effect of dietary NE concentration and feeding level on carcass, noncarcass, and empty body chemical composition of barrows at 25 kg of BW1,2     NE,4 Mcal/kg  Feeding level,5%    P-value  Item  ISG3  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  6  18  18  18  18  18  18          Carcass  Water, g/kg  713  703  699  691  702  700  691  3  0.010  0.010  0.003  Protein, g/kg  160  176  173  170  174  174  170  2  0.003  0.080  0.967  Lipid, g/kg  91  83  90  104  86  87  104  3  <0.001  <0.001  0.002  Ash, g/kg  34.0  33.5  33.9  32.3  34.3  33.6  31.8  0.6  0.090  0.004  0.518  GE,6 Mcal/kg  1.72  1.74  1.78  1.90  1.75  1.77  1.91  0.02  <0.001  <0.001  0.007  Noncarcass  Water, g/kg  821  800  798  796  800  798  795  1  0.305  0.096  0.206  Protein, g/kg  142  159  159  161  159  160  159  1  0.526  0.621  0.619  Lipid, g/kg  20  23  24  25  23  23  26  1  0.186  0.073  0.468  Ash, g/kg  11.1  12.4  12.5  12.4  12.3  12.4  12.7  0.3  0.911  0.609  0.285  GE,6 Mcal/kg  1.01  1.13  1.15  1.17  1.14  1.15  1.17  0.01  0.106  0.103  0.161  Empty body  Water, g/kg  733  721  718  711  720  718  711  3  0.025  0.040  0.004  Protein, g/kg  156  173  170  168  171  172  168  2  0.012  0.074  0.918  Lipid, g/kg  77  72  78  89  74  76  89  2  <0.001  <0.001  0.003  Ash, g/kg  29.6  29.5  30.0  28.6  30.3  29.7  28.0  0.6  0.064  <0.001  0.482  GE,6 Mcal/kg  1.59  1.63  1.66  1.76  1.64  1.65  1.76  0.02  <0.001  <0.001  0.006  GE,7 Mcal/kg  1.62  1.66  1.70  1.79  1.67  1.69  1.79  0.02  0.002  0.003  0.006      NE,4 Mcal/kg  Feeding level,5%    P-value  Item  ISG3  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  6  18  18  18  18  18  18          Carcass  Water, g/kg  713  703  699  691  702  700  691  3  0.010  0.010  0.003  Protein, g/kg  160  176  173  170  174  174  170  2  0.003  0.080  0.967  Lipid, g/kg  91  83  90  104  86  87  104  3  <0.001  <0.001  0.002  Ash, g/kg  34.0  33.5  33.9  32.3  34.3  33.6  31.8  0.6  0.090  0.004  0.518  GE,6 Mcal/kg  1.72  1.74  1.78  1.90  1.75  1.77  1.91  0.02  <0.001  <0.001  0.007  Noncarcass  Water, g/kg  821  800  798  796  800  798  795  1  0.305  0.096  0.206  Protein, g/kg  142  159  159  161  159  160  159  1  0.526  0.621  0.619  Lipid, g/kg  20  23  24  25  23  23  26  1  0.186  0.073  0.468  Ash, g/kg  11.1  12.4  12.5  12.4  12.3  12.4  12.7  0.3  0.911  0.609  0.285  GE,6 Mcal/kg  1.01  1.13  1.15  1.17  1.14  1.15  1.17  0.01  0.106  0.103  0.161  Empty body  Water, g/kg  733  721  718  711  720  718  711  3  0.025  0.040  0.004  Protein, g/kg  156  173  170  168  171  172  168  2  0.012  0.074  0.918  Lipid, g/kg  77  72  78  89  74  76  89  2  <0.001  <0.001  0.003  Ash, g/kg  29.6  29.5  30.0  28.6  30.3  29.7  28.0  0.6  0.064  <0.001  0.482  GE,6 Mcal/kg  1.59  1.63  1.66  1.76  1.64  1.65  1.76  0.02  <0.001  <0.001  0.006  GE,7 Mcal/kg  1.62  1.66  1.70  1.79  1.67  1.69  1.79  0.02  0.002  0.003  0.006  1 Data are least squares means of 54 individually housed barrows (6 barrows per NE × feeding level combination). 2 Carcass is the eviscerated pig including the head and feet; noncarcass is the pooled individual organs including emptied gastrointestinal tract and blood; empty body is the sum of the carcass and noncarcass. 3 Data of the initial slaughter group (ISG; n = 6) were used to estimate the initial body composition of the experimental pigs and were not included in the statistical analysis. Body weight at slaughter was 9.4 ± 1.0 kg (mean ± SD). 4 Net enegy concentration of each diet across feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 5 In the 100% treatment group, pigs within treatment were allowed unrestricted access to experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 6 Bomb calorimeter analysis. 7 Calculated from analyzed protein and lipid content by using 5.66 and 9.46 kcal/g for protein and lipids, respectively (Ewan, 2001). View Large Ash concentration in carcass and empty body tended to decline with increased dietary NE concentration (P < 0.10) and declined with increasing feeding level (P < 0.01). Except for a tendency for water and lipid concentrations in noncarcass to decline and increase, respectively, with increasing feeding level (P < 0.10), there were no effects of dietary NE concentration and feeding level on the chemical composition of non-carcass. A NE × feeding level interaction was detected in water, lipid, and GE concentrations in carcass and empty body (P < 0.01; Table 7). The interaction was illustrated by a reduced water concentration and by increased lipid and GE concentrations in the carcass and empty body of pigs given ad libitum access to the high-NE concentration diet. Nutrient Deposition Rates and Ratios The rates of water, protein, lipid, and ash deposition and RE in noncarcass were not affected by dietary NE concentration (Table 8) but were increased with increasing feeding level (P < 0.001). Ash:protein and water:protein ratios were not affected by NE concentration and feeding level in the noncarcass fraction. Table 8. Effect of dietary NE concentration and feeding level on deposition rates of water, protein, lipids, ash and energy retention in the carcass and noncarcass of barrows between 9 and 25 kg1,2   NE,3 Mcal/kg  Feeding level,4%    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level      Pigs, n  18  18  18  18  18  18          Carcass      Water, g/d  288  285  295  257  272  339  4  0.230  <0.001  0.171      Protein, g/d  77  75  77  67  72  89  2  0.174  <0.001  0.113      Lipid, g/d  33  37  51  30  34  57  3  <0.001  <0.001  <0.001      Ash, g/d  13.7  13.9  13.7  12.8  13.2  15.3  0.5  0.905  <0.001  0.033      Lipid:protein ratio  0.42  0.49  0.64  0.45  0.47  0.63  0.02  <0.001  <0.001  0.002      Water:protein ratio  3.74  3.83  3.87  3.83  3.79  3.82  0.08  0.277  0.856  0.541      Ash:protein ratio  0.18  0.19  0.18  0.19  0.18  0.17  0.01  0.169  0.009  0.436      RE,5 Mcal/d  0.73  0.75  0.90  0.65  0.71  1.02  0.02  <0.001  <0.001  <0.001  Noncarcass      Water, g/d  76  74  78  64  68  97  3  0.692  <0.001  0.767      Protein, g/d  16  16  17  14  15  21  1  0.312  <0.001  0.819      Lipid, g/d  2.4  2.6  2.9  2.0  2.2  3.6  0.2  0.189  <0.001  0.426      Ash, g/d  1.3  1.3  1.3  1.0  1.2  1.7  0.1  0.918  <0.001  0.325      Lipid:protein ratio  0.14  0.16  0.17  0.15  0.14  0.17  0.01  0.260  0.074  0.619      Water:protein ratio  4.63  4.64  4.55  4.63  4.57  4.63  0.08  0.715  0.812  0.553      Ash:protein ratio  0.079  0.079  0.078  0.078  0.076  0.082  0.003  0.927  0.445  0.149      RE,5 Mcal/d  0.12  0.12  0.13  0.10  0.11  0.16  0.01  0.246  <0.001  0.591    NE,3 Mcal/kg  Feeding level,4%    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level      Pigs, n  18  18  18  18  18  18          Carcass      Water, g/d  288  285  295  257  272  339  4  0.230  <0.001  0.171      Protein, g/d  77  75  77  67  72  89  2  0.174  <0.001  0.113      Lipid, g/d  33  37  51  30  34  57  3  <0.001  <0.001  <0.001      Ash, g/d  13.7  13.9  13.7  12.8  13.2  15.3  0.5  0.905  <0.001  0.033      Lipid:protein ratio  0.42  0.49  0.64  0.45  0.47  0.63  0.02  <0.001  <0.001  0.002      Water:protein ratio  3.74  3.83  3.87  3.83  3.79  3.82  0.08  0.277  0.856  0.541      Ash:protein ratio  0.18  0.19  0.18  0.19  0.18  0.17  0.01  0.169  0.009  0.436      RE,5 Mcal/d  0.73  0.75  0.90  0.65  0.71  1.02  0.02  <0.001  <0.001  <0.001  Noncarcass      Water, g/d  76  74  78  64  68  97  3  0.692  <0.001  0.767      Protein, g/d  16  16  17  14  15  21  1  0.312  <0.001  0.819      Lipid, g/d  2.4  2.6  2.9  2.0  2.2  3.6  0.2  0.189  <0.001  0.426      Ash, g/d  1.3  1.3  1.3  1.0  1.2  1.7  0.1  0.918  <0.001  0.325      Lipid:protein ratio  0.14  0.16  0.17  0.15  0.14  0.17  0.01  0.260  0.074  0.619      Water:protein ratio  4.63  4.64  4.55  4.63  4.57  4.63  0.08  0.715  0.812  0.553      Ash:protein ratio  0.079  0.079  0.078  0.078  0.076  0.082  0.003  0.927  0.445  0.149      RE,5 Mcal/d  0.12  0.12  0.13  0.10  0.11  0.16  0.01  0.246  <0.001  0.591  1 Data are least squares means of 54 individually housed barrows (6 barrows per NE × feeding level combination). 2 Carcass is the eviscerated pig including the head and feet; noncarcass is the pooled individual organs including emptied gastrointestinal tract and blood. 3 Net energy concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 4 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 5 RE = retained energy. View Large Table 8. Effect of dietary NE concentration and feeding level on deposition rates of water, protein, lipids, ash and energy retention in the carcass and noncarcass of barrows between 9 and 25 kg1,2   NE,3 Mcal/kg  Feeding level,4%    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level      Pigs, n  18  18  18  18  18  18          Carcass      Water, g/d  288  285  295  257  272  339  4  0.230  <0.001  0.171      Protein, g/d  77  75  77  67  72  89  2  0.174  <0.001  0.113      Lipid, g/d  33  37  51  30  34  57  3  <0.001  <0.001  <0.001      Ash, g/d  13.7  13.9  13.7  12.8  13.2  15.3  0.5  0.905  <0.001  0.033      Lipid:protein ratio  0.42  0.49  0.64  0.45  0.47  0.63  0.02  <0.001  <0.001  0.002      Water:protein ratio  3.74  3.83  3.87  3.83  3.79  3.82  0.08  0.277  0.856  0.541      Ash:protein ratio  0.18  0.19  0.18  0.19  0.18  0.17  0.01  0.169  0.009  0.436      RE,5 Mcal/d  0.73  0.75  0.90  0.65  0.71  1.02  0.02  <0.001  <0.001  <0.001  Noncarcass      Water, g/d  76  74  78  64  68  97  3  0.692  <0.001  0.767      Protein, g/d  16  16  17  14  15  21  1  0.312  <0.001  0.819      Lipid, g/d  2.4  2.6  2.9  2.0  2.2  3.6  0.2  0.189  <0.001  0.426      Ash, g/d  1.3  1.3  1.3  1.0  1.2  1.7  0.1  0.918  <0.001  0.325      Lipid:protein ratio  0.14  0.16  0.17  0.15  0.14  0.17  0.01  0.260  0.074  0.619      Water:protein ratio  4.63  4.64  4.55  4.63  4.57  4.63  0.08  0.715  0.812  0.553      Ash:protein ratio  0.079  0.079  0.078  0.078  0.076  0.082  0.003  0.927  0.445  0.149      RE,5 Mcal/d  0.12  0.12  0.13  0.10  0.11  0.16  0.01  0.246  <0.001  0.591    NE,3 Mcal/kg  Feeding level,4%    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level      Pigs, n  18  18  18  18  18  18          Carcass      Water, g/d  288  285  295  257  272  339  4  0.230  <0.001  0.171      Protein, g/d  77  75  77  67  72  89  2  0.174  <0.001  0.113      Lipid, g/d  33  37  51  30  34  57  3  <0.001  <0.001  <0.001      Ash, g/d  13.7  13.9  13.7  12.8  13.2  15.3  0.5  0.905  <0.001  0.033      Lipid:protein ratio  0.42  0.49  0.64  0.45  0.47  0.63  0.02  <0.001  <0.001  0.002      Water:protein ratio  3.74  3.83  3.87  3.83  3.79  3.82  0.08  0.277  0.856  0.541      Ash:protein ratio  0.18  0.19  0.18  0.19  0.18  0.17  0.01  0.169  0.009  0.436      RE,5 Mcal/d  0.73  0.75  0.90  0.65  0.71  1.02  0.02  <0.001  <0.001  <0.001  Noncarcass      Water, g/d  76  74  78  64  68  97  3  0.692  <0.001  0.767      Protein, g/d  16  16  17  14  15  21  1  0.312  <0.001  0.819      Lipid, g/d  2.4  2.6  2.9  2.0  2.2  3.6  0.2  0.189  <0.001  0.426      Ash, g/d  1.3  1.3  1.3  1.0  1.2  1.7  0.1  0.918  <0.001  0.325      Lipid:protein ratio  0.14  0.16  0.17  0.15  0.14  0.17  0.01  0.260  0.074  0.619      Water:protein ratio  4.63  4.64  4.55  4.63  4.57  4.63  0.08  0.715  0.812  0.553      Ash:protein ratio  0.079  0.079  0.078  0.078  0.076  0.082  0.003  0.927  0.445  0.149      RE,5 Mcal/d  0.12  0.12  0.13  0.10  0.11  0.16  0.01  0.246  <0.001  0.591  1 Data are least squares means of 54 individually housed barrows (6 barrows per NE × feeding level combination). 2 Carcass is the eviscerated pig including the head and feet; noncarcass is the pooled individual organs including emptied gastrointestinal tract and blood. 3 Net energy concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 4 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 5 RE = retained energy. View Large The rates of water, protein, and ash deposition in carcass were not affected by dietary NE concentration. In addition, the ash:protein ratio decreased in carcass (P < 0.001) with increasing feeding level, but the water:protein ratio was not affected by either dietary NE concentration or feeding level. However, a NE × feeding level interaction was detected in carcass LD, LD:PD ratio, and RE (P < 0.001). The results of empty body deposition rates of water, protein, lipid, ash, LD:PD ratio, water:protein ratio, ash:protein ratio, and RE are shown in Table 9. Reflective of the effect on carcass and noncarcass, the rates of water, protein, and ash deposition, and the protein:water and ash:protein ratios in empty body were not affected by dietary NE concentration. In contrast, water, protein, and ash deposition rates were increased with increasing feeding level (P < 0.01). The ash:protein ratio decreased with increasing feeding level (P < 0.05), whereas the water:protein ratio was unaffected by feeding level. A NE × feeding level interaction was detected in RE:energy intake ratios (RE:GE, RE:DE, RE:ME, and RE:NE; P < 0.01; Table 9). Table 9. Effect of dietary NE concentration and feeding level on deposition rates of water, protein, lipid, ash, and energy retention in the empty body of barrows fed between 9 and 25 kg1,2   NE,3 Mcal/kg  Feeding level,4 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  18  18  18  18  18  18          Water, g/d  364  359  374  321  341  436  6  0.288  <0.001  0.325  Protein, g/d  93  90  94  81  87  110  2  0.211  <0.001  0.151  Lipid, g/d  35  40  54  33  36  60  3  0.001  <0.001  0.001  Ash, g/d  15.0  15.2  15.0  13.9  14.4  17.0  0.5  0.934  <0.001  0.076  Lipid:protein ratio  0.37  0.44  0.55  0.40  0.41  0.55  0.02  <0.001  <0.001  0.002  Water:protein ratio  3.90  3.97  4.00  3.97  3.92  3.98  0.07  0.440  0.717  0.411  Ash:protein ratio  0.16  0.17  0.16  0.17  0.16  0.15  0.01  0.184  0.004  0.473  RE,5 Mcal/d  0.85  0.87  1.03  0.75  0.82  1.18  0.03  <0.001  <0.001  0.001  RE,6 Mcal/d  0.86  0.88  1.05  0.77  0.84  1.19  0.03  <0.001  <0.001  0.001  RE as protein,6 Mcal/d  0.53  0.51  0.53  0.46  0.49  0.62  0.01  0.211  <0.001  0.152  RE as lipids,6 Mcal/d  0.33  0.37  0.51  0.31  0.34  0.57  0.02  <0.001  <0.001  0.001  RE as protein,7 % of RE  62.1  58.3  53.3  60.4  59.8  53.5  1.3  <0.001  <0.001  0.052  RE as lipids,7 % of RE  37.9  41.7  46.7  39.6  40.2  46.5  1.3  <0.001  <0.001  0.052  RE:GE intake  0.22  0.23  0.26  0.23  0.22  0.25  0.01  <0.001  <0.001  0.002  RE:DE intake  0.26  0.27  0.30  0.26  0.26  0.31  0.01  <0.001  <0.001  0.001  RE:ME intake  0.28  0.29  0.32  0.28  0.28  0.32  0.01  <0.001  <0.001  0.001  RE:NE intake  0.41  0.41  0.44  0.40  0.40  0.46  0.01  0.004  <0.001  0.001    NE,3 Mcal/kg  Feeding level,4 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  18  18  18  18  18  18          Water, g/d  364  359  374  321  341  436  6  0.288  <0.001  0.325  Protein, g/d  93  90  94  81  87  110  2  0.211  <0.001  0.151  Lipid, g/d  35  40  54  33  36  60  3  0.001  <0.001  0.001  Ash, g/d  15.0  15.2  15.0  13.9  14.4  17.0  0.5  0.934  <0.001  0.076  Lipid:protein ratio  0.37  0.44  0.55  0.40  0.41  0.55  0.02  <0.001  <0.001  0.002  Water:protein ratio  3.90  3.97  4.00  3.97  3.92  3.98  0.07  0.440  0.717  0.411  Ash:protein ratio  0.16  0.17  0.16  0.17  0.16  0.15  0.01  0.184  0.004  0.473  RE,5 Mcal/d  0.85  0.87  1.03  0.75  0.82  1.18  0.03  <0.001  <0.001  0.001  RE,6 Mcal/d  0.86  0.88  1.05  0.77  0.84  1.19  0.03  <0.001  <0.001  0.001  RE as protein,6 Mcal/d  0.53  0.51  0.53  0.46  0.49  0.62  0.01  0.211  <0.001  0.152  RE as lipids,6 Mcal/d  0.33  0.37  0.51  0.31  0.34  0.57  0.02  <0.001  <0.001  0.001  RE as protein,7 % of RE  62.1  58.3  53.3  60.4  59.8  53.5  1.3  <0.001  <0.001  0.052  RE as lipids,7 % of RE  37.9  41.7  46.7  39.6  40.2  46.5  1.3  <0.001  <0.001  0.052  RE:GE intake  0.22  0.23  0.26  0.23  0.22  0.25  0.01  <0.001  <0.001  0.002  RE:DE intake  0.26  0.27  0.30  0.26  0.26  0.31  0.01  <0.001  <0.001  0.001  RE:ME intake  0.28  0.29  0.32  0.28  0.28  0.32  0.01  <0.001  <0.001  0.001  RE:NE intake  0.41  0.41  0.44  0.40  0.40  0.46  0.01  0.004  <0.001  0.001  1 Data are least squares means of 54 individually housed barrows (6 barrows per NE × feeding level combination). 2 Empty body is the sum of the carcass and noncarcass. 3 Net energy concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 4 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 5 RE = retained energy, bomb calorimeter analysis. 6 Retained energy was calculated from protein and lipid deposition rates as 5.66 and 9.46 kcal/g for protein and lipids, respectively (Ewan, 2001). 7 Percentage of RE as protein and lipids of the calculated RE values. View Large Table 9. Effect of dietary NE concentration and feeding level on deposition rates of water, protein, lipid, ash, and energy retention in the empty body of barrows fed between 9 and 25 kg1,2   NE,3 Mcal/kg  Feeding level,4 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  18  18  18  18  18  18          Water, g/d  364  359  374  321  341  436  6  0.288  <0.001  0.325  Protein, g/d  93  90  94  81  87  110  2  0.211  <0.001  0.151  Lipid, g/d  35  40  54  33  36  60  3  0.001  <0.001  0.001  Ash, g/d  15.0  15.2  15.0  13.9  14.4  17.0  0.5  0.934  <0.001  0.076  Lipid:protein ratio  0.37  0.44  0.55  0.40  0.41  0.55  0.02  <0.001  <0.001  0.002  Water:protein ratio  3.90  3.97  4.00  3.97  3.92  3.98  0.07  0.440  0.717  0.411  Ash:protein ratio  0.16  0.17  0.16  0.17  0.16  0.15  0.01  0.184  0.004  0.473  RE,5 Mcal/d  0.85  0.87  1.03  0.75  0.82  1.18  0.03  <0.001  <0.001  0.001  RE,6 Mcal/d  0.86  0.88  1.05  0.77  0.84  1.19  0.03  <0.001  <0.001  0.001  RE as protein,6 Mcal/d  0.53  0.51  0.53  0.46  0.49  0.62  0.01  0.211  <0.001  0.152  RE as lipids,6 Mcal/d  0.33  0.37  0.51  0.31  0.34  0.57  0.02  <0.001  <0.001  0.001  RE as protein,7 % of RE  62.1  58.3  53.3  60.4  59.8  53.5  1.3  <0.001  <0.001  0.052  RE as lipids,7 % of RE  37.9  41.7  46.7  39.6  40.2  46.5  1.3  <0.001  <0.001  0.052  RE:GE intake  0.22  0.23  0.26  0.23  0.22  0.25  0.01  <0.001  <0.001  0.002  RE:DE intake  0.26  0.27  0.30  0.26  0.26  0.31  0.01  <0.001  <0.001  0.001  RE:ME intake  0.28  0.29  0.32  0.28  0.28  0.32  0.01  <0.001  <0.001  0.001  RE:NE intake  0.41  0.41  0.44  0.40  0.40  0.46  0.01  0.004  <0.001  0.001    NE,3 Mcal/kg  Feeding level,4 %    P-value  Item  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  18  18  18  18  18  18          Water, g/d  364  359  374  321  341  436  6  0.288  <0.001  0.325  Protein, g/d  93  90  94  81  87  110  2  0.211  <0.001  0.151  Lipid, g/d  35  40  54  33  36  60  3  0.001  <0.001  0.001  Ash, g/d  15.0  15.2  15.0  13.9  14.4  17.0  0.5  0.934  <0.001  0.076  Lipid:protein ratio  0.37  0.44  0.55  0.40  0.41  0.55  0.02  <0.001  <0.001  0.002  Water:protein ratio  3.90  3.97  4.00  3.97  3.92  3.98  0.07  0.440  0.717  0.411  Ash:protein ratio  0.16  0.17  0.16  0.17  0.16  0.15  0.01  0.184  0.004  0.473  RE,5 Mcal/d  0.85  0.87  1.03  0.75  0.82  1.18  0.03  <0.001  <0.001  0.001  RE,6 Mcal/d  0.86  0.88  1.05  0.77  0.84  1.19  0.03  <0.001  <0.001  0.001  RE as protein,6 Mcal/d  0.53  0.51  0.53  0.46  0.49  0.62  0.01  0.211  <0.001  0.152  RE as lipids,6 Mcal/d  0.33  0.37  0.51  0.31  0.34  0.57  0.02  <0.001  <0.001  0.001  RE as protein,7 % of RE  62.1  58.3  53.3  60.4  59.8  53.5  1.3  <0.001  <0.001  0.052  RE as lipids,7 % of RE  37.9  41.7  46.7  39.6  40.2  46.5  1.3  <0.001  <0.001  0.052  RE:GE intake  0.22  0.23  0.26  0.23  0.22  0.25  0.01  <0.001  <0.001  0.002  RE:DE intake  0.26  0.27  0.30  0.26  0.26  0.31  0.01  <0.001  <0.001  0.001  RE:ME intake  0.28  0.29  0.32  0.28  0.28  0.32  0.01  <0.001  <0.001  0.001  RE:NE intake  0.41  0.41  0.44  0.40  0.40  0.46  0.01  0.004  <0.001  0.001  1 Data are least squares means of 54 individually housed barrows (6 barrows per NE × feeding level combination). 2 Empty body is the sum of the carcass and noncarcass. 3 Net energy concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 4 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 5 RE = retained energy, bomb calorimeter analysis. 6 Retained energy was calculated from protein and lipid deposition rates as 5.66 and 9.46 kcal/g for protein and lipids, respectively (Ewan, 2001). 7 Percentage of RE as protein and lipids of the calculated RE values. View Large Net energy × feeding level interactions in LD, the LD:PD ratio, RE, and RE as lipids were detected (P < 0.001; Table 9). The interaction of NE and feeding level on LD, the LD:PD ratio, and RE in carcass and empty body illustrates the increased LD, LD:PD ratio, and RE in the carcass and empty body of pigs given ad libitum access to the high-NE concentration diet as compared with lower energy diets. Physical Body Composition at Slaughter Carcass, noncarcass, and empty BW were not affected by NE concentration. In addition, carcass, non-carcass, and empty BW expressed as a percentage of live BW were not affected by NE concentration (Table 10). In addition, carcass BW, EBW, and EBW as a percentage of live BW were not affected by feeding level. Noncarcass weight and noncarcass weight as a percentage of live BW increased up to 10 and 7%, respectively, with increasing feeding level (P < 0.05). In contrast, carcass weight as a percentage of live BW declined up to 2% with increasing feeding level (P < 0.05). Table 10. Effect of dietary NE content and feeding level on physical body composition at slaughter of barrows at 25 kg of BW1,2     NE,4 Mcal/kg  Feeding level, 5 %    P-value  Item  ISG3  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  6  18  18  18  18  18  18          Weight, kg      Carcass  7.1  18.4  18.8  18.8  18.6  18.8  18.5  0.3  0.280  0.707  0.165      Noncarcass  1.6  4.2  4.2  4.3  4.1  4.2  4.5  0.1  0.623  0.012  0.628      Empty body  8.7  22.6  23.0  23.1  22.7  23.0  23.0  0.3  0.188  0.691  0.206  Weight, g/kg of live BW      Carcass  746  743  749  750  754  751  736  5  0.530  0.023  0.137      Noncarcass  173  170  169  172  166  168  177  4  0.739  0.037  0.623      Empty body  919  913  918  923  921  920  914  3  0.195  0.327  0.146  Organ weight, g      Empty digestive tract  716  1,761  1,779  1,800  1,735  1,730  1,854  50  0.928  0.049  0.524      Blood  391  893  922  998  881  960  971  39  0.162  0.226  0.782      Liver  258  807  790  789  745  775  867  25  0.842  0.003  0.456      Heart  62  149  152  146  147  154  147  5  0.612  0.400  0.707      Lung  122  351  352  357  365  344  351  16  0.970  0.641  0.409      Kidneys  59  178  166  174  165  165  188  5  0.281  0.004  0.137      Spleen  21  69  73  71  70  68  74  6  0.876  0.713  0.236  Organ weight, g/kg of EBW6      Empty digestive tract  83  78  77  77  76  75  81  3  0.895  0.058  0.336      Blood  45  39  40  43  39  42  42  2  0.235  0.246  0.714      Liver  30  36  34  34  33  34  38  1  0.520  0.005  0.426      Heart  6.9  6.6  6.6  6.3  6.5  6.7  6.4  0.2  0.519  0.459  0.652      Lung  14.3  15.6  15.3  15.4  16.1  15.0  15.3  0.7  0.971  0.533  0.470      Kidneys  7.1  7.9  7.2  7.5  7.3  7.2  8.2  0.2  0.180  0.008  0.067      Spleen  2.2  3.1  3.2  3.0  3.1  3.0  3.2  0.2  0.920  0.726  0.214      NE,4 Mcal/kg  Feeding level, 5 %    P-value  Item  ISG3  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  6  18  18  18  18  18  18          Weight, kg      Carcass  7.1  18.4  18.8  18.8  18.6  18.8  18.5  0.3  0.280  0.707  0.165      Noncarcass  1.6  4.2  4.2  4.3  4.1  4.2  4.5  0.1  0.623  0.012  0.628      Empty body  8.7  22.6  23.0  23.1  22.7  23.0  23.0  0.3  0.188  0.691  0.206  Weight, g/kg of live BW      Carcass  746  743  749  750  754  751  736  5  0.530  0.023  0.137      Noncarcass  173  170  169  172  166  168  177  4  0.739  0.037  0.623      Empty body  919  913  918  923  921  920  914  3  0.195  0.327  0.146  Organ weight, g      Empty digestive tract  716  1,761  1,779  1,800  1,735  1,730  1,854  50  0.928  0.049  0.524      Blood  391  893  922  998  881  960  971  39  0.162  0.226  0.782      Liver  258  807  790  789  745  775  867  25  0.842  0.003  0.456      Heart  62  149  152  146  147  154  147  5  0.612  0.400  0.707      Lung  122  351  352  357  365  344  351  16  0.970  0.641  0.409      Kidneys  59  178  166  174  165  165  188  5  0.281  0.004  0.137      Spleen  21  69  73  71  70  68  74  6  0.876  0.713  0.236  Organ weight, g/kg of EBW6      Empty digestive tract  83  78  77  77  76  75  81  3  0.895  0.058  0.336      Blood  45  39  40  43  39  42  42  2  0.235  0.246  0.714      Liver  30  36  34  34  33  34  38  1  0.520  0.005  0.426      Heart  6.9  6.6  6.6  6.3  6.5  6.7  6.4  0.2  0.519  0.459  0.652      Lung  14.3  15.6  15.3  15.4  16.1  15.0  15.3  0.7  0.971  0.533  0.470      Kidneys  7.1  7.9  7.2  7.5  7.3  7.2  8.2  0.2  0.180  0.008  0.067      Spleen  2.2  3.1  3.2  3.0  3.1  3.0  3.2  0.2  0.920  0.726  0.214  1 Data are least squares means of 54 individually housed barrows (6 barrows per NE × feeding level combination). 2 Carcass is the eviscerated pig including the head and feet; noncarcass is the pooled individual organ including emptied gastrointestinal tract and blood; empty body is the sum of the carcass and noncarcass. 3 Data of the initial slaughter group (ISG; n = 6) were not included in the statistical analysis; the BW at slaughter was 9.4 ± 1.0 kg (mean ± SD). 4 Net energy concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 5 In the 100% treatment group, pigs within treatment were allowed unrestricted access to experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 6 EBW = empty BW. View Large Table 10. Effect of dietary NE content and feeding level on physical body composition at slaughter of barrows at 25 kg of BW1,2     NE,4 Mcal/kg  Feeding level, 5 %    P-value  Item  ISG3  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  6  18  18  18  18  18  18          Weight, kg      Carcass  7.1  18.4  18.8  18.8  18.6  18.8  18.5  0.3  0.280  0.707  0.165      Noncarcass  1.6  4.2  4.2  4.3  4.1  4.2  4.5  0.1  0.623  0.012  0.628      Empty body  8.7  22.6  23.0  23.1  22.7  23.0  23.0  0.3  0.188  0.691  0.206  Weight, g/kg of live BW      Carcass  746  743  749  750  754  751  736  5  0.530  0.023  0.137      Noncarcass  173  170  169  172  166  168  177  4  0.739  0.037  0.623      Empty body  919  913  918  923  921  920  914  3  0.195  0.327  0.146  Organ weight, g      Empty digestive tract  716  1,761  1,779  1,800  1,735  1,730  1,854  50  0.928  0.049  0.524      Blood  391  893  922  998  881  960  971  39  0.162  0.226  0.782      Liver  258  807  790  789  745  775  867  25  0.842  0.003  0.456      Heart  62  149  152  146  147  154  147  5  0.612  0.400  0.707      Lung  122  351  352  357  365  344  351  16  0.970  0.641  0.409      Kidneys  59  178  166  174  165  165  188  5  0.281  0.004  0.137      Spleen  21  69  73  71  70  68  74  6  0.876  0.713  0.236  Organ weight, g/kg of EBW6      Empty digestive tract  83  78  77  77  76  75  81  3  0.895  0.058  0.336      Blood  45  39  40  43  39  42  42  2  0.235  0.246  0.714      Liver  30  36  34  34  33  34  38  1  0.520  0.005  0.426      Heart  6.9  6.6  6.6  6.3  6.5  6.7  6.4  0.2  0.519  0.459  0.652      Lung  14.3  15.6  15.3  15.4  16.1  15.0  15.3  0.7  0.971  0.533  0.470      Kidneys  7.1  7.9  7.2  7.5  7.3  7.2  8.2  0.2  0.180  0.008  0.067      Spleen  2.2  3.1  3.2  3.0  3.1  3.0  3.2  0.2  0.920  0.726  0.214      NE,4 Mcal/kg  Feeding level, 5 %    P-value  Item  ISG3  2.15  2.26  2.37  70  80  100  SEM  NE  Feeding level  NE × feeding level  Pigs, n  6  18  18  18  18  18  18          Weight, kg      Carcass  7.1  18.4  18.8  18.8  18.6  18.8  18.5  0.3  0.280  0.707  0.165      Noncarcass  1.6  4.2  4.2  4.3  4.1  4.2  4.5  0.1  0.623  0.012  0.628      Empty body  8.7  22.6  23.0  23.1  22.7  23.0  23.0  0.3  0.188  0.691  0.206  Weight, g/kg of live BW      Carcass  746  743  749  750  754  751  736  5  0.530  0.023  0.137      Noncarcass  173  170  169  172  166  168  177  4  0.739  0.037  0.623      Empty body  919  913  918  923  921  920  914  3  0.195  0.327  0.146  Organ weight, g      Empty digestive tract  716  1,761  1,779  1,800  1,735  1,730  1,854  50  0.928  0.049  0.524      Blood  391  893  922  998  881  960  971  39  0.162  0.226  0.782      Liver  258  807  790  789  745  775  867  25  0.842  0.003  0.456      Heart  62  149  152  146  147  154  147  5  0.612  0.400  0.707      Lung  122  351  352  357  365  344  351  16  0.970  0.641  0.409      Kidneys  59  178  166  174  165  165  188  5  0.281  0.004  0.137      Spleen  21  69  73  71  70  68  74  6  0.876  0.713  0.236  Organ weight, g/kg of EBW6      Empty digestive tract  83  78  77  77  76  75  81  3  0.895  0.058  0.336      Blood  45  39  40  43  39  42  42  2  0.235  0.246  0.714      Liver  30  36  34  34  33  34  38  1  0.520  0.005  0.426      Heart  6.9  6.6  6.6  6.3  6.5  6.7  6.4  0.2  0.519  0.459  0.652      Lung  14.3  15.6  15.3  15.4  16.1  15.0  15.3  0.7  0.971  0.533  0.470      Kidneys  7.1  7.9  7.2  7.5  7.3  7.2  8.2  0.2  0.180  0.008  0.067      Spleen  2.2  3.1  3.2  3.0  3.1  3.0  3.2  0.2  0.920  0.726  0.214  1 Data are least squares means of 54 individually housed barrows (6 barrows per NE × feeding level combination). 2 Carcass is the eviscerated pig including the head and feet; noncarcass is the pooled individual organ including emptied gastrointestinal tract and blood; empty body is the sum of the carcass and noncarcass. 3 Data of the initial slaughter group (ISG; n = 6) were not included in the statistical analysis; the BW at slaughter was 9.4 ± 1.0 kg (mean ± SD). 4 Net energy concentration of each diet among feeding levels as estimated from digestible nutrients (Centraal Veevoederbureau, 1994). 5 In the 100% treatment group, pigs within treatment were allowed unrestricted access to experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. 6 EBW = empty BW. View Large No effect of NE concentration was detected for individual organ weights or for organ weights as a percentage of empty body (Table 10). There were 7, 14, and 16% increases in empty digestive tract, kidney, and liver weights, respectively, with increasing feeding level (P < 0.05). These organ weights as a percentage of EBW tended to increase in a manner similar to the level of intakes (P < 0.06). Blood, heart, lung, and spleen weights (and as a percentage of empty body) were not affected by dietary NE concentration and feeding level. Plasma IGF-I Concentrations There was no effect of dietary NE concentration on plasma IGF-I concentrations (Table 11). However, IGF-I concentrations increased with increasing feeding level and were greater on d 21 than on d 7 (P < 0.001), indicative of the increasing ADG over this time frame. Table 11. Effect of dietary NE concentration, feeding level and collection time on plasma IGF-I concentrations (ng/ mL) in barrows from 9 to 25 kg fed diets with increasing NE concentration at 3 feeding levels1 NE, Mcal/kg  Feeding level,2 %  d 7  d 21  2.15  70  61  99    80  59  141    100  101  233  2.26  70  60  110    80  60  79    100  111  242  2.37  70  60  104    80  70  134    100  112  277  SEM    16  16  P-value      NE  0.223          Feeding level  <0.001          Day  <0.001          NE × d  0.383          NE × feeding level  0.242          Feeding level × d  <0.001          NE × feeding level × d  0.392      NE, Mcal/kg  Feeding level,2 %  d 7  d 21  2.15  70  61  99    80  59  141    100  101  233  2.26  70  60  110    80  60  79    100  111  242  2.37  70  60  104    80  70  134    100  112  277  SEM    16  16  P-value      NE  0.223          Feeding level  <0.001          Day  <0.001          NE × d  0.383          NE × feeding level  0.242          Feeding level × d  <0.001          NE × feeding level × d  0.392      1 Data are least squares means. The experiment included a total of 81 individually housed barrows (9 barrows per NE × feeding level combination). Blood samples were collected from pigs on d 7 and 21. 2 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. View Large Table 11. Effect of dietary NE concentration, feeding level and collection time on plasma IGF-I concentrations (ng/ mL) in barrows from 9 to 25 kg fed diets with increasing NE concentration at 3 feeding levels1 NE, Mcal/kg  Feeding level,2 %  d 7  d 21  2.15  70  61  99    80  59  141    100  101  233  2.26  70  60  110    80  60  79    100  111  242  2.37  70  60  104    80  70  134    100  112  277  SEM    16  16  P-value      NE  0.223          Feeding level  <0.001          Day  <0.001          NE × d  0.383          NE × feeding level  0.242          Feeding level × d  <0.001          NE × feeding level × d  0.392      NE, Mcal/kg  Feeding level,2 %  d 7  d 21  2.15  70  61  99    80  59  141    100  101  233  2.26  70  60  110    80  60  79    100  111  242  2.37  70  60  104    80  70  134    100  112  277  SEM    16  16  P-value      NE  0.223          Feeding level  <0.001          Day  <0.001          NE × d  0.383          NE × feeding level  0.242          Feeding level × d  <0.001          NE × feeding level × d  0.392      1 Data are least squares means. The experiment included a total of 81 individually housed barrows (9 barrows per NE × feeding level combination). Blood samples were collected from pigs on d 7 and 21. 2 In the 100% treatment group, pigs within treatment were allowed unrestricted access to the experimental diets; 80 and 70% were the respective feed allowances based on the feed consumption on a BW basis of pigs within each dietary NE concentration. View Large Correlations Among Performance, Empty Body Composition, DE, and NE The results of correlation analyses are shown in Table 12. Average daily gain and ADFI were positively correlated with DEi and NEi (P < 0.001), but not with G:F. Furthermore, empty body lipid concentration, LD, PD, and the LD:PD ratio were all positively correlated with DEi and NEi (P < 0.001). Empty body CP concentration was weakly negatively correlated with NEi (P < 0.05). Table 12. Correlations among measured DE intake, calculated NE intake and performance, empty body nutrient content, and deposition rates in barrows between 9 and 25 kg fed diets with increasing NE concentration at 3 feeding levels1,2 Variable  Correlation coefficient  P-value  DE intake, and      ADG  0.9157  <0.001      ADFI  0.9862  <0.001      G:F  −0.1350  0.230      Measured DE concentration  −0.4776  <0.001      Empty body CP content  −0.2347  0.088      Empty body lipid content  0.6005  <0.001      Empty body PD  0.9261  <0.001      Empty body LD  0.8003  <0.001      Empty body LD:PD ratio  0.6004  <0.001  NE intake, and      ADG  0.8982  <0.001      ADFI  0.9636  <0.001      G:F ratio  −0.1219  0.278      Calculated NE concentration  −0.0803  0.476      Empty body CP content  −0.2858  0.036      Empty body lipid content  0.6592  <0.001      Empty body PD  0.907  <0.001      Empty body LD  0.848  <0.001      Empty body LD:PD ratio  0.666  <0.001  Variable  Correlation coefficient  P-value  DE intake, and      ADG  0.9157  <0.001      ADFI  0.9862  <0.001      G:F  −0.1350  0.230      Measured DE concentration  −0.4776  <0.001      Empty body CP content  −0.2347  0.088      Empty body lipid content  0.6005  <0.001      Empty body PD  0.9261  <0.001      Empty body LD  0.8003  <0.001      Empty body LD:PD ratio  0.6004  <0.001  NE intake, and      ADG  0.8982  <0.001      ADFI  0.9636  <0.001      G:F ratio  −0.1219  0.278      Calculated NE concentration  −0.0803  0.476      Empty body CP content  −0.2858  0.036      Empty body lipid content  0.6592  <0.001      Empty body PD  0.907  <0.001      Empty body LD  0.848  <0.001      Empty body LD:PD ratio  0.666  <0.001  1 Correlation coefficients were computed by using individual barrows' measured DE and calculated NE concentrations; n = 81, performance variables; n = 54, empty body parameters. 2 PD = protein deposition; LD = lipid deposition; and LD:PD = protein:lipid ratio. View Large Table 12. Correlations among measured DE intake, calculated NE intake and performance, empty body nutrient content, and deposition rates in barrows between 9 and 25 kg fed diets with increasing NE concentration at 3 feeding levels1,2 Variable  Correlation coefficient  P-value  DE intake, and      ADG  0.9157  <0.001      ADFI  0.9862  <0.001      G:F  −0.1350  0.230      Measured DE concentration  −0.4776  <0.001      Empty body CP content  −0.2347  0.088      Empty body lipid content  0.6005  <0.001      Empty body PD  0.9261  <0.001      Empty body LD  0.8003  <0.001      Empty body LD:PD ratio  0.6004  <0.001  NE intake, and      ADG  0.8982  <0.001      ADFI  0.9636  <0.001      G:F ratio  −0.1219  0.278      Calculated NE concentration  −0.0803  0.476      Empty body CP content  −0.2858  0.036      Empty body lipid content  0.6592  <0.001      Empty body PD  0.907  <0.001      Empty body LD  0.848  <0.001      Empty body LD:PD ratio  0.666  <0.001  Variable  Correlation coefficient  P-value  DE intake, and      ADG  0.9157  <0.001      ADFI  0.9862  <0.001      G:F  −0.1350  0.230      Measured DE concentration  −0.4776  <0.001      Empty body CP content  −0.2347  0.088      Empty body lipid content  0.6005  <0.001      Empty body PD  0.9261  <0.001      Empty body LD  0.8003  <0.001      Empty body LD:PD ratio  0.6004  <0.001  NE intake, and      ADG  0.8982  <0.001      ADFI  0.9636  <0.001      G:F ratio  −0.1219  0.278      Calculated NE concentration  −0.0803  0.476      Empty body CP content  −0.2858  0.036      Empty body lipid content  0.6592  <0.001      Empty body PD  0.907  <0.001      Empty body LD  0.848  <0.001      Empty body LD:PD ratio  0.666  <0.001  1 Correlation coefficients were computed by using individual barrows' measured DE and calculated NE concentrations; n = 81, performance variables; n = 54, empty body parameters. 2 PD = protein deposition; LD = lipid deposition; and LD:PD = protein:lipid ratio. View Large DISCUSSION The current study investigated the interaction of NE concentration and daily feed intake, an approach never before considered in the weanling pig. Bikker et al. (1995), Quiniou et al. (1995), and Weis et al. (2004) studied the effect of varying energy supply, achieved by controlling daily feed intake, on growth performance and body composition in growing pigs, but we could find no references in the literature to similar studies in the weanling pig. In contrast, there have been numerous studies on the effect of energy concentration on the growth performance of weanling pigs. For example, Tokach et al. (1995), Reis de Souza et al. (2000), and Levesque (2002) evaluated increasing ME, GE, or DE, respectively, on performance. However, no one has investigated the interaction of dietary energy concentration and daily feed intake. In studies of energy utilization, it is important that the AA supply is adequate and that marginal deficiencies do not confound experimental results. We confirmed in a preliminary trial (Oresanya et al., 2006) that the experimental model used here could avoid confounding by the AA supply if daily feed intake restriction was less than 30%. Furthermore, the optimal total Lys:DE ratio used in the current study was 5% greater than the required ratio determined in a previous experiment (Oresanya et al., 2007) using the same genetics in the same barn. As a final guard against AA insufficiency, selected ingredients were preassayed for AA content prior to diet formulation. We also confirmed, by using a factorial approach to determining the Lys requirement, that AA intake was not limiting performance. According to the results of a previous study (Oresanya et al., 2007) and those reported by Levesque (2002), measured DE and calculated NE values may differ from formulated values. For a more accurate interpretation of results and to confirm that dietary energy concentration was indeed varied, NE was determined by using the actual digestibility of individual components of the diet and applying the Centraal Veevoederbureau (1994) prediction equation. Although the calculated NE values of diets were lower than formulated, the range of NE among the diets was virtually identical to those intended (220 and 210 kcal, respectively). The range in measured DE differed from formulated DE (140 vs. 90 kcal), illustrating once again the importance of measuring dietary energy concentration directly in studies focused on the utilization of dietary energy. It has long been recognized that energy concentration is an important determinant of voluntary feed intake of pigs (NRC, 1987; Lewis, 2001), with feed intake declining as energy concentration increases. However, in the current study, increasing dietary NE concentration did not affect feed intake. Reis de Souza et al. (2000) reported no effect on feed intake with DE concentration increasing from 3.24 to 3.50 Mcal/kg in weaned pigs between 7 to 25 kg of BW. Conversely, Levesque (2002) showed a 6.3% decline in feed intake of weaned pigs between 7 to 20 kg of BW when the measured DE concentration increased from 3.18 to 3.59 Mcal of DE/kg. In our previous study (Oresanya, 2005), increasing the NE concentration reduced the feed intake of pigs. It is generally accepted that dietary energy concentration is not the only factor affecting feed intake in the weaned pig (Patience et al., 1995). Certain dietary factors, for example, bulkiness (Whittemore et al., 2001) and fat content (e.g., Xing et al., 2004), exert direct or indirect physiological effects that may reduce feed intake. Because dietary fat is suggested to reduce the digesta passage rate (Azain, 2001), elevated dietary fat concentration may act as a constraint on feed intake, and may explain part of the reduction in feed intake observed in other studies when dietary energy concentration was increased (Van Lunen and Cole, 1998; Smith et al., 1999; Levesque, 2002). Dietary fat concentration was increased from the low to the high energy diet by 13.1, 6.8, and 8.2%, respectively, in the aforementioned studies compared with only 5.4% in the current study. The results of the current study suggest that because feed intake was not highly correlated with dietary energy concentration, the physiological effect of dietary components may be an important factor in determining feed intake above the simple NE concentration. Similar to feed intake, feed efficiency was not affected by dietary NE concentration. This is contrary to our previous studies in which feed efficiency was improved with increasing DE concentration (Levesque, 2002; Oresanya et al., 2007). Feed efficiency would be expected to increase either when a reduction in feed intake occurs without changes in growth rate (Pettigrew and Moser, 1991; Xing et al., 2004) or an increase in growth rate occurs without any change in feed intake. However, the end point in the current study was a constant BW, whereas most growth studies are conducted to a constant length of feeding period. Thus, if pigs require more time to reach a given BW end point, this will inevitably affect G:F because longer feeding periods are associated with increased maintenance feed requirements, for example, more days on test. Because the pigs did not reduce their feed intake as dietary NE concentration increased, NEi also increased (Table 4). This observation is consistent with the suggestion that weaned pigs have a limited ability to regulate energy intake based on energy density (NRC, 1987). However, it must be noted that DEi calculated from the measured DE concentration in the diet was not affected by dietary treatment. This would suggest that the response of weaned pigs to energy concentration should be expressed in terms of the total available energy equivalent (i.e., calculated NEi). This is supported by a stronger correlation between empty body composition and nutrient deposition rates with NEi as compared with DEi. The observation that NEi increased with increased dietary NE concentration, without increasing the growth rate, strongly suggests that pigs fed the low-NE diet were able to consume sufficient energy to maximize growth rate. The adequacy of the low-NE diet was further confirmed by the decreased slope observed when comparing ADG against NEi among the 3 diets (Figure 1); the increase in ADG per unit of NEi was decreased on the high-NE diet. Contrary to the response of ADG to changes in NE concentration, increasing daily feed intake did increase ADG. However, body protein concentration tended to decline with increased feed intake, whereas NE concentration interacted with feed intake on both body water and lipid content in the empty body. As discussed below, the results of empty body composition and nutrient deposition rates further support the adequacy of the low-NE diet. Little is known about the interactive effects of dietary energy concentration and feed (energy) intake on the chemical composition of the body of the weaned pig. A previous study by Campbell and Dunkin (1983) reported a decline in empty body protein concentration with increasing energy intake in pigs growing between 7 and 19 kg of BW. Conversely, empty body lipid concentration increased with energy intake, but at a greater rate in pigs fed the low-CP diet compared with the high-CP diet (Campbell and Dunkin, 1983). In the current study, empty body protein concentration declined with increasing NE concentration, but not feeding level. In contrast, an interaction of NE concentration and feeding level in empty body water and lipid content resulted in decreased water content and greater lipid content in the empty body of pigs with unrestricted access to the high-NE diet compared with pigs on the other treatments. The increase in noncarcass weight to increased feeding level in the current study was predominantly due to an increase in the weight of the gastrointestinal tract, liver, and kidneys (Table 10). Bikker (1994) indicated that the metabolically active organs (intestines, liver, kidneys, and pancreas) are very sensitive to the amount and type of nutrients ingested. The decline in carcass weight with increasing feeding level may be due to an increase in gut fill at greater feeding levels (Bikker, 1994). The effect of feeding level on noncarcass weight in the current study is consistent with those reported in growing pigs by other workers (Rao and McCracken, 1992; Bikker et al., 1995, 1996; Gomez et al., 2002). Together, these results suggest that the adverse effects of increasing NE concentration, in terms of body chemical composition, but not in terms of physical composition, may explain the lack of improved BW gain in the weaned pig when dietary energy concentration is increased. In the current study, protein, water, and ash deposition rates in the empty body were not affected by dietary NE concentration, but were increased with increasing feeding level. Research in growing pigs has reported a concomitant increase in protein, water, and ash with increasing feeding level (Bikker et al., 1995; Quiniou et al., 1995, 1996; Gomez et al., 2002). As observed in other studies that evaluated the response of weaned pigs to energy intake (Gädecken et al., 1985; Kyriazakis and Emmans, 1992; Collin et al., 2001), the present results indicate that weaned pigs deposited more protein than lipids. Empty body PD increased with increasing feeding level but was not affected by dietary NE concentration. Similarly, empty body LD increased with increasing feeding level, but unlike PD, NE concentration interacted with feeding level on LD. Indeed, a 95% greater LD was observed in pigs given ad libitum access to the high-NE diet compared with the low-NE diet. The increase in empty body PD and LD with increasing feeding level observed in the current study is consistent with studies in growing pigs (Campbell et al., 1983; Bikker et al., 1995). It is well recognized that PD increases linearly with increasing energy intake when the diet is limiting only in energy (de Lange et al., 2001). Assuming that increasing the dietary energy concentration is a way to increase lean growth, remove the limitation from physical gut capacity, or both, one might expect PD to increase with increased NE concentration. Data from the current study revealed that only LD, and not PD, increased with increasing dietary NE concentration. Contrary to the preceding assumption, this study demonstrates that increasing energy concentration may increase only LD in weaned pigs. The lipid:protein ratio is an indicator of the associated variations of BW gain (Whittemore and Fawcett, 1976) and of lean growth. It assumes that below the maximum PD, the LD:PD ratio is constant and independent of BW (Whittemore and Fawcett, 1976) and energy intake (Whittemore, 1983). In the current study, the LD:PD ratio was increased concomitant with an increase in energy intake with increasing NE concentration (Figure 1). This demonstrates that the LD:PD ratio in the weaned pig is increased by both energy intake and energy concentration. Indeed, the LD:PD ratio in the empty body increased by 38 and 49% with increasing feeding level and energy concentration, respectively. Clearly, increasing the supply of utilizable energy through any means appears to increase the LD:PD ratio. There was no relationship between NEi and LD:PD ratio on the low- and medium-NE diets. However, because of the increase in LD:PD ratio in pigs allowed unrestricted access to the high-NE diet, the LD:PD ratio increased linearly with NEig, that is, the quantity of NE consumed above maintenance (R2 = 0.78; P < 0.05; Figure 1). This further demonstrates a negative effect of increasing NE from 2.15 to 2.37 Mcal/kg on the lean growth of pigs. In general, the effect of dietary NE concentration and feeding level on water and ash deposition rates in carcass, noncarcass, and empty body closely resembled the effect described for PD. In fact, these 3 chemical components in the body are known to be closely associated (Kotarbinska, 1971; de Greef, 1992). Thus, the empty body water:protein ratio was constant among dietary NE concentrations and feeding levels. Likewise, the ash:protein ratio was not influenced by dietary NE concentration (mean = 0.16). However, because empty body PD increased at a faster rate than ash, the ash:protein ratio declined with increasing feeding level. In contrast, Kyriazakis and Emmans (1992) showed that energy intake of pigs between 12 to 28 kg of BW did not change the empty body ash:protein ratio (0.19). Increasing the NE concentration increased the amount of lipid deposited per megacalorie of energy (Table 4). This may be related to the increase in dietary fat content and intake. Chudy and Schiemann (1969) indicated that dietary fat is utilized with a greater efficiency for body lipid deposition than carbohydrates. This is due to lower heat losses associated with the incorporation of dietary fatty acids into body lipids. Daily LD was related to digestible fat intake (r = 0.71, P < 0.001). However, LD was equally related to starch intake (r = 0.88, P < 0.001). The decreased efficiency of energy utilization for growth with increasing NE concentration (Table 4 and Figure 1) and feeding level is clearly due to the changing body composition, as demonstrated by the decline in empty body protein and increase in lipid content. Because 1 kg of lean muscle contains 77 to 80% water, compared with only 5% for adipose tissue, the energy cost of lean growth is considerably less than adipose tissue deposition (NRC, 1998). Furthermore, mostly because of an increase in LD, there were increases in the RE:DE, RE:ME, and RE:NE ratios with increasing NE concentration and energy intake (interaction, P < 0.001; Table 9). Our estimate of 118 kcal/kg of BW0.75 per d for DEim is similar to the 122 kcal/kg of BW0.75 per d for weaned pigs estimated by Campbell and Dunkin (1983) and the estimate of 110 kcal/kg of BW0.75 per d reported by the NRC (1998). Our estimated NE for maintenance (71 kcal/kg of BW0.75 per d) agrees with that reported by Robles and Ewan (1982) and is similar to the 78 kcal/kg of BW0.75 per d reported by Just (1982). Insulin-like growth factors, and particularly IGF-I, mediate the growth-stimulating action of GH (Simmen et al., 1998) and GH-dependent increases in PD (Boyd and Bauman, 1989). Circulating IGF-I reflects endogenous GH secretion and overall growth in well-nourished humans and animals (Blum et al., 1993; Simmen et al., 1998). The effect of an increasing dietary energy concentration and feeding level on circulating concentrations of IGF-I in the weaned pig has not previously been established. Feeding level, and not NE concentration, had a considerable effect on plasma IGF-I in the current study (Table 11). The lack of effect of dietary NE concentration on plasma IGF-I concentrations is consistent with that of Lee et al. (2002), who showed that increasing dietary DE concentrations from 2.95 to 3.50 Mcal/kg in growing pigs from 59 to 105 kg of BW did not affect serum IGF-I concentrations. Buonomo et al. (1987) indicated that circulating concentrations of IGF-I are positively correlated with growth rate in pigs. Plasma IGF-I concentrations in the current study increased 105% from d 7 to 21, and are consistent with the increase in growth rate within that period. On the basis of these results, we conclude that the response of the pig to changes in dietary energy concentration differ from those accruing from changes in daily feed intake. Consequently, one must be very careful in extrapolating conclusions about energy utilization obtained under restricted feed intake regimens to commercial conditions in which the dietary energy concentration is being changed. The few instances reported herein of interaction between changes in NE concentration and changes in feed intake suggest that in many respects, the outcomes as they relate to energy utilization are quite different. Because NE correlates more closely than DE with LD and LD:PD, we are also able to conclude that NEi offers an advantage over DEi in predicting body composition and rate of gain in weanling pigs. The results of the current study indicate that increasing the dietary NE concentration increased energy intake, body lipid content, and deposition rate, but not protein deposition rate. Thus, in future studies of energy utilization, there is a clear need to consider both total BW gain and the composition of that gain. Furthermore, we must be careful when making adjustments to the energy concentration of practical diets based on the results of experiments using restricted feed intake, because the pig clearly responds differently to the 2 situations. As a final point, it should be noted that these results were obtained with 1 genetic population; the response to energy supply may differ among different genotypes. LITERATURE CITED AOAC 1990. Official Methods of Analysis.  15th ed. Assoc. Offic. Anal. Chem., Arlington, VA. AOAC 2002. Official Methods of Analysis.  17th ed. Vol 2. Assoc. Offic. Anal. Chem., Arlington, VA. PubMed PubMed  Azain, M. J. 2001. Fat in swine nutrition. Pages 95– 106 in Swine Nutrition.  A. J. Lewis and L. L. Southern ed. CRC Press LLC, Boca Raton, FL. Google Scholar CrossRef Search ADS   Bach Knudsen, K. E., and J. A. Hansen 1991. Gastrointestinal implications in pigs of wheat and oat fractions. I. Digestibility and bulking properties of polysaccharides and other major constituents. Br. J. Nutr.  65: 217– 232. Google Scholar CrossRef Search ADS PubMed  Bikker, P. 1994. Protein and lipid accretion in body components of growing pigs. Effects of body weight and nutrient intake. PhD Thesis. Wageningen Agricultural University,  Wageningen, the Netherlands. Bikker, P., V. Karabinas, M. W. A. Verstegen, and R. G. Campbell 1995. Protein and lipid accretion in body components of growing gilts (20 to 45 kilograms) as affected by energy intake. J. Anim. Sci.  73: 2355– 2363. Google Scholar CrossRef Search ADS PubMed  Bikker, P., M. W. A. Verstegen, B. Kemp, and M. W. Bosch 1996. Performance and body composition of finishing gilts (45 to 85 kilograms) as affected by energy intake and nutrition in earlier life: I. Growth of the body and body components. J. Anim. Sci.  74: 806– 816. Google Scholar CrossRef Search ADS PubMed  Blum, W. F., K. Albertsson-Wikland, S. Rosberg, and M. B. Ranke 1993. Serum levels of insulin-like growth factor I (IGF-I) and IGF binding protein 3 reflect spontaneous growth hormone secretion. J. Clin. Endocrinol. Metab.  76: 1610– 1616. Google Scholar PubMed  Boyd, R. D., and D. E. Bauman 1989. Mechanisms of action for somatotropin in growth. Pages 257– 293 in Animal Growth Regulation.  D. R. Campion, G. J. Hausman, and R. J. Martin ed. Plenum Publishing, New York, NY. Google Scholar CrossRef Search ADS   Buonomo, F. C., T. J. Lauterio, C. A. Baile, and D. R. Campion 1987. Determination of insulin-like growth factor I (IGF1) and IGF binding protein levels in swine. Domest. Anim. Endocrinol.  4: 23– 31. Google Scholar CrossRef Search ADS PubMed  Campbell, R. G., and A. C. Dunkin 1983. The influence of dietary protein and energy intake on the performance, body composition and energy utilization of pigs growing from 7 to 19 kg. Anim. Prod.  36: 185– 192. Campbell, R. G., M. R. Taverner, and D. M. Curic 1983. The influence of feeding level from 20 to 45 kg live weight on the performance and body composition of female and entire male pigs. Anim. Prod.  36: 193– 199. Canadian Council on Animal Care 1993. Guide to the Care and Use of Experimental Animals.  2nd ed. Vol. 1. E. D. Olfert, B. M. Cross, and A. A. McWilliam ed. CCAC, Ottawa, Ontario, Canada. Centraal Veevoederbureau 1994. Table of Feedstuffs. Information about Composition, Digestibility and Feeding Values.  Centraal Veevoederbureau, Lelystad, the Netherlands. Centraal Veevoederbureau 1998. Table of Feedstuffs. Information about Composition, Digestibility and Feeding Values.  Centraal Veevoederbureau, Lelystad, the Netherlands. Chudy, A., and R. Schiemann 1969. Utilization of dietary fat for maintenance and fat deposition in model studies with rats. Page 161 in Energy Metabolism of Farm Animals.  K. L. Blaxter, J. Kielanowski, and G. Thorbek ed. Eur. Assoc. Anim. Prod. Publ. 26. Butterworths, London, UK. Collin, A., J. van Milgen, S. Dubois, and J. Noblet 2001. Effect of high temperature and feeding level on energy utilization in piglets. J. Anim. Sci.  79: 1849– 1857. Google Scholar CrossRef Search ADS PubMed  Daughaday, W. H., I. K. Mariz, and S. L. Blethen 1980. Inhibition of access of bound somatomedin to membrane receptor and immunobinding sites: A comparison of radioreceptor and radio-immunoassay of somatomedin in native and acid-ethanol-extracted serum. J. Clin. Endocrinol. Metab.  51: 781– 788. Google Scholar CrossRef Search ADS PubMed  de Greef, K. H. 1992. Prediction of production: Nutritional induced tissue partitioning in growing pigs. PhD Thesis. Wageningen Agric. Univ.,  Wageningen, the Netherlands. de Lange, C. F. M., S. H. Birkett, and P. C. H. Morel 2001. Protein, fat, and bone tissue growth in swine. Pages 65– 84 in Swine Nutrition.  A. J. Lewis and L. L. Southern ed. CRC Press LLC, Boca Raton, FL. Ewan, R. C. 2001. Energy utilization in swine nutrition. Pages 85– 94 in Swine Nutrition.  A. J. Lewis and L. L. Southern ed. CRC Press LLC, Boca Raton, FL. Englyst, H. N. 1989. Classification and measurement of plant polysaccharides. Anim. Feed Sci. Technol.  3: 27– 42. Google Scholar CrossRef Search ADS   Englyst, H. N., and G. J. Hudson 1987. Colorimetric method for routine measurement of dietary fiber as non-starch polysaccharides. A comparison with gas-liquid chromatography. Food Chem.  24: 63– 76. Google Scholar CrossRef Search ADS   Gädecken, D., H. J. Oslage, and H. Bohme 1985. Energy requirement for maintenance and energy costs of protein and fat deposition in piglets. Arch. Tierernaehr.  35: 481– 494. Google Scholar CrossRef Search ADS   Gomez, R. S., A. J. Lewis, P. S. Miller, H. Y. Chen, and R. M. Diedrichsen 2002. Body compositon and tissue accretion rates of barrows fed corn-soybean meal diets or low-protein, amino acid-supplemented diets at different feeding levels. J. Anim. Sci.  80: 654– 662. Google Scholar CrossRef Search ADS PubMed  Graham, H., K. Hesselman, and P. Aman 1986. The influence of wheat bran and sugar-beet pulp on the digestibility of dietary components in a cereal-based pig diet. J. Nutr.  116: 242– 251. Google Scholar CrossRef Search ADS PubMed  Gregory, N. G., B. W. Moss, and R. H. Leeson 1987. An assessment of carbon dioxide stunning in pigs. Vet. Rec.  121: 517– 518. Google Scholar CrossRef Search ADS PubMed  Hoenderken, R. 1983. Electrical and carbon dioxide stunning of pigs for slaughter. Pages 59– 63 in Stunning of Animals for Slaughter.  G. Eikelenboom ed. Martinus Nijhoff Publishers, Boston, MA. Just, A. 1982. The net energy value of balanced diets for growing pigs. Livest. Prod. Sci.  8: 541– 555. Google Scholar CrossRef Search ADS   Kerr, D. E., B. Laarveld, and J. G. Manns 1990. Effects of passive immunization of growing guinea-pigs with an insulin-like growth factor-I monoclonal antibody. J. Endocrinol.  124: 403– 415. Google Scholar CrossRef Search ADS PubMed  Kotarbinska, M. 1971. The chemical composition of the body in growing pigs. Roczniki Nauk Rol  B-93: 129– 135. Kyriazakis, I., and G. C. Emmans 1992. The effects of varying protein and energy intakes on the growth and body composition of pigs. 1. The effects of energy intake at constant, high protein intake. Br. J. Nutr.  68: 603– 613. Google Scholar CrossRef Search ADS PubMed  Kyriazakis, I., and G. C. Emmans 1999. Voluntary feed intake and diet selection. Pages 229– 248 in A Quantitative Biology of the Pig.  I. Kyriazakis ed. CAB Int., Wallingford, UK. Lee, C. Y., H. P. Lee, J. H. Jeong, K. H. Baik, S. K. Jin, J. H. Lee, and S. H. Sohn 2002. Effects of restricted feeding, low-energy diet, and implantation of trenbolone acetate plus estradiol on growth, carcass traits, and circulating concentrations of insulin-like growth factor (IGF)-I and IGF-binding protein-3 in finishing barrows. J. Anim. Sci.  80: 84– 93. Google Scholar CrossRef Search ADS PubMed  Levesque, C. L. 2002. The effects of dietary digestible energy concentration and site of weaning on weanling pig performance. MSc Thesis. University of Saskatchewan, Saskatoon, Canada. Lewis, A. J. 2001. Amino acids in swine nutrition. Pages 131– 150 in Swine Nutrition.  A. J. Lewis and L. L. Southern ed. CRC Press LLC, Boca Raton, FL. Littell, R. C., P. R. Henry, and C. B. Ammerman 1998. Statistical analysis of repeated measures data using SAS procedures. J. Anim. Sci.  76: 1216– 1231. Google Scholar CrossRef Search ADS PubMed  Llames, C. R., and J. Fontaine 1994. Determination of amino acids in feeds: Collaborative study. J. AOAC Int.  77: 1362– 1402. McCarthy, J. F., F. X. Aherne, and D. B. Okai 1974. Use of HCl insoluble ash as an index material for determining apparent digestibility with pigs. Can. J. Anim. Sci.  54: 107– 109. Google Scholar CrossRef Search ADS   Noblet, J., and J. M. Perez 1993. Prediction of digestibility of nutrients and energy values of pig diets from chemical analysis. J. Anim. Sci.  71: 3389– 3398. Google Scholar CrossRef Search ADS PubMed  NRC 1987. Predicting Feed Intake of Food-Producing Animals.  Natl. Acad. Press, Washington, DC. NRC 1998. Nutrient Requirements of Swine.  10th ed. National Acad. Press, Washington, DC. Oresanya, T. F. 2005. Energy Metabolism in the Weanling Pig: Effects of Energy Concentration and Intake on Growth, Body Composition and Nutrient Accretion in the Empty Body. PhD Thesis, University of Saskatchewan,  Saskatoon, Canada. Oresanya, T. F., A. D. Beaulieu, E. Beltranena, and J. F. Patience 2007. The effect of dietary energy concentration and total lysine/digestible energy ratio on the growth performance of weaned pigs. Can. J. Anim. Sci.  87: 45– 55. Google Scholar CrossRef Search ADS   Oresanya, T. F., A. D. Beaulieu, and J. F. Patience 2006. The effect of reducing energy intake on the performance of weaned barrows when amino acid intake declines either in direct proportion to energy or at a reduced rate. Can. J. Anim. Sci.  86: 273– 277. Google Scholar CrossRef Search ADS   Oresanya, T. F., J. F. Patience, R. T. Zijlstra, A. D. Beaulieu, D. M. Middleton, B. R. Blakley, and D. A. Gillis 2003. Defining the tolerable level of ergot in the diet of weaned pigs. Can. J. Anim. Sci.  83: 493– 500. Google Scholar CrossRef Search ADS   Patience, J. F., R. E. Austic, and R. D. Boyd 1987. Effect of dietary electrolyte balance on growth and acid-base status in swine. J. Anim. Sci.  64: 457– 466. Google Scholar CrossRef Search ADS PubMed  Patience, J. F., P. Thacker, and C. F. M. de Lange 1995. Swine Nutrition Guide.  2nd edition. Prairie Swine Centre Inc., Univ. of Saskatchewan, Saskatoon, Canada. Pettigrew, J. E., and R. L. Moser 1991. Fat in swine nutrition. Pages 133– 145 in Swine Nutrition.  E. R. Miller, D. E. Ullrey, and A. J. Lewis ed. Butterworth-Heinemann, Stoneham, MA. Google Scholar CrossRef Search ADS   Quiniou, N., J. Noblet, and J. Y. Dourmad 1996. Effect of energy intake on the performance of different types of pig from 45 to 100 kg body weight. 2. Tissue gain. Anim. Sci.  63: 289– 296. Google Scholar CrossRef Search ADS   Quiniou, N., J. Noblet, J. van Milgen, and J. Y. Dourmad 1995. Effect of energy intake on performance, nutrient and tissue gain and protein and energy utilization in growing boars. Anim. Sci.  61: 133– 143. Google Scholar CrossRef Search ADS   Rao, D. S., and K. J. McCracken 1992. Energy:protein interaction in growing boars of high genetic potential for lean growth. 2. Effects on chemical composition of gain and whole-body protein turn-over. Anim. Prod.  54: 83– 93. Google Scholar CrossRef Search ADS   Reis de Souza, T. C., A. Aumaitre, J. Mourot, and J. Peiniau 2000. Effect of graded level of tallow in the diet on performance, digestibility of fat, lipogenesis and body lipid deposition of the weaned piglet. Asian-Australas. J. Anim. Sci.  13: 497– 505. Google Scholar CrossRef Search ADS   Robles, A., and R. C. Ewan 1982. Utilization of energy of rice and rice bran by young pigs. J. Anim. Sci.  55: 572– 577. Google Scholar CrossRef Search ADS   Simmen, F. A., L. Badinga, M. L. Green, I. Kwak, S. Song, and R. C. Simmen 1998. The porcine insulin-like growth factor system: At the interface of nutrition, growth and reproduction. J. Nutr.  128: 315S– 320S. Google Scholar PubMed  Smith, J. W., II, M. D. Tokach, J. L. Nelssen, and R. D. Goodband 1999. Effects of lysine:calorie ratio on growth performance of 10- to 25-kilogram pigs. J. Anim. Sci.  77: 3000– 3006. Google Scholar CrossRef Search ADS PubMed  Tokach, M. D., J. E. Pettigrew, L. J. Johnson, M. Overland, J. W. Rust, and S. G. Cornelius 1995. Effect of adding fat and(or) milk products to the weanling pig diets on performance in the nursery and subsequent grow-finish stages. J. Anim. Sci.  73: 3358– 3368. Google Scholar CrossRef Search ADS PubMed  Van Lunen, T. A., and D. J. A. Cole 1998. The effect of dietary energy concentration and lysine/digestible energy ratio on growth performance and nitrogen deposition of young hybrid pigs. Anim. Sci.  67: 117– 129. Google Scholar CrossRef Search ADS   Veum, T. L., M. S. Carlson, C. W. Wu, D. W. Bollinger, and M. R. Ellersieck 2004. Copper proteinate in weanling pig diets for enhancing growth performance and reducing fecal copper excretion compared with copper sulfate. J. Anim. Sci.  82: 1062– 1070. Google Scholar CrossRef Search ADS PubMed  Wang, Z., and L. A. Goonewardene 2004. The use of mixed models in the analysis of animal experiments with repeated measures data. Can. J. Anim. Sci.  84: 1– 11. Google Scholar CrossRef Search ADS   Weis, R. N., S. H. Birkett, P. C. H. Morel, and C. F. M. de Lange 2004. Effect of energy intake and body weight on physical and chemical body composition in growing entire male pigs. J. Anim. Sci.  82: 109– 121. Google Scholar CrossRef Search ADS PubMed  Whittemore, C. T. 1983. Development of recommended energy and protein allowances for growing pigs. Agric. Syst.  11: 159. Google Scholar CrossRef Search ADS   Whittemore, C. T., and R. H. Fawcett 1976. Theoretical aspects of a flexible model to simulate protein and lipid growth in pigs. Anim. Prod.  22: 87– 96. Google Scholar CrossRef Search ADS   Whittemore, C. T., I. Kyriazakis, G. C. Emmans, and B. J. Tolkamp 2001. Tests of two theories of food intake using growing pigs 1. The effect of ambient temperature on the intake of foods of differing bulk content. Anim. Sci.  72: 351– 360. Xing, J. J., E. van Heugten, D. F. Li, K. J. Touchette, J. A. Coalson, and J. Odle 2004. Effects of emulsification, fat encapsulation, and pelleting on weanling pig performance and nutrient digestibility. J. Anim. Sci.  82: 2601– 2609. Google Scholar CrossRef Search ADS PubMed  Zar, J. H. 1984. Biostatistical analysis. Pages 292– 305 in Comparing Simple Linear Regression Equations.  Prentice-Hall, Englewood Cliffs, NJ. Footnotes 1 Funding for this project was provided by the National Sciences and Engineering Research Council of Canada (NSERC, Ottawa, Ontario, Canada). We acknowledge with gratitude the overall research program funding to the Prairie Swine Centre from the Saskatchewan Pork Development Board (Saskatoon, Saskatchewan, Canada), Alberta Pork (Edmonton, Alberta, Canada), the Manitoba Pork Council (Winnipeg, Manitoba, Canada), and the Agriculture Development Fund of Saskatchewan (Regina, Saskatchewan, Canada). We also thank Degussa Corporation (Allendale, NJ) for AA assays. The mention of a trade name, specific product, or equipment does not represent a warranty or guarantee to the exclusion of others that may be equally suitable. Copyright 2008 Journal of Animal Science This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com
TI - Investigations of energy metabolism in weanling barrows: The interaction of dietary energy concentration and daily feed (energy) intake
JF - Journal of Animal Science
DO - 10.2527/jas.2007-0009
DA - 2008-02-01
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