TY - JOUR
AU - Theil, Peter, K
AB - Abstract The objective of the current study was to determine the optimal concentration of dietary standardized ileal digestible (SID) Lys required to maximize litter gain and minimize sow BW loss in modern high-yielding lactating sows when SID CP was kept constant across dietary treatments. A total of 396 parity 1 to 5 sows (L × Y, DanBred, Herlev, Denmark) were included in the study from day 3 after farrowing until weaning at day 26. Sows were allocated to 6 dietary treatments increasing in SID Lys concentration (6.19, 6.90, 7.63, 8.33, 9.04, and 9.76 g/kg). Diets were isoenergetic (14.04 MJ ME/kg as-fed). Litters were standardized to 14 piglets at day 3 ± 2 d postpartum. At day 3 ± 2 d and at day 26 ± 3 d in lactation, litter weight, and sow BW and back fat were registered. On a subsample of 72 parity 2 to 4 sows, litters were additionally weighed at days 10 and 17 ± 3 d, and milk and blood were sampled at day 3 ± 2 d, and 10, 17 and at 24 ± 3 d in lactation. For the 72 sows, body pools of fat and protein were also determined at days 3 ± 2 and 26 ± 3 d using the D2O dilution technique. All data were analyzed as a randomized complete block design using PROC MIXED in SAS. Furthermore, data were subjected to linear and quadratic polynomial contrasts. Variables with quadratic or linear effects or days in milk × treatment interactions were selected for analysis in PROC NLMIXED using linear broken-line models to evaluate optimal SID Lys concentrations. Only models that converged and the best fitting models were included. Average daily litter gain increased until a breakpoint at 8.11 g/kg of SID Lys (as-fed). At and above the breakpoint, multiparous and primiparous sows had litter gains of 3.36 and 2.93 kg/d, respectively. Weaning litter size (13.0 ± 0.1) was similar between the 6 dietary treatments (P = 0.28). Lactation sow BW loss was minimized to 0.17 kg/d at 9.05 g/kg of SID Lys and sow body protein loss was minimized to 0.23 kg at 9.22 g/kg of SID Lys. Linear broken-line analyses showed that for 3, 10, 17, and 24 DIM, plasma urea was minimized at 7.02, 8.10, 8.73, and 8.32 g/kg of SID Lys, respectively, and milk fat was maximized at 7.80 g/kg of SID Lys. In conclusion, in our conditions, high-yielding lactating sows required 8.11 g/kg of SID Lys to maximize litter gain and 9.05 g/kg of SID Lys to minimize sow BW loss. Based on plasma urea, the optimal dietary concentration of SID Lys was lowest in week 1, intermediate in week 2 and 4, and greatest in week 3 of lactation. Introduction Lysine is considered the first-limiting amino acid in cereal-soybean meal-based diets fed to lactating sows (Danielsen, 1992). Previous estimates of dietary standardized ileal digestible (SID) Lys requirements for lactating sows vary considerably from 27 to 70 g/d or 4.9 to 10.5 g/kg diet (NRC, 2012; Xue et al., 2012; Gourley et al., 2017). However, most of the research investigating the dietary Lys requirement was conducted with sows weaning <10 piglets per litter and with litter growth rates of 1.4 to 2.3 kg/d (NRC, 2012), whereas Gourley et al. (2017) reported that sows required 70 g/d of SID Lys for a litter growth rate of 2.9 kg/d. Today, sows may wean more than 13 piglets per litter and produce more than 3 kg of litter growth (Hojgaard et al., 2019a, 2019b). At peak lactation, 95% of the daily SID Lys requirement is associated with milk production (Feyera and Theil, 2017). Consequently, great amounts of milk are required today (Hansen et al., 2012) which seems to increase the dietary Lys requirement. Factors such as genetics, age, nursing litter size, appetite, and feed ingredients may affect the dietary Lys requirement. Furthermore, when formulating diets, other essential amino acids are provided relative to Lys, which emphasize the need for determining the dietary Lys requirement for high-yielding sows under commercial European conditions. Several studies have estimated the dietary Lys requirement of lactating sows when supplied via intact protein sources (King et al., 1993; Yang et al., 2000; Gourley et al., 2017). However, very few studies have used the approach of increasing dietary Lys while keeping all other amino acids and nutrients constant (Chen et al., 1978; Knabe et al., 1996; Xue et al., 2012) and none of these had litter growth rates above 2.5 kg/d. The objective of the present study was to estimate the optimal dietary SID Lys supply required to maximize litter gain and minimize sow BW loss in high-yielding lactating sows when fed increasing levels of SID Lys and slightly oversupplied with other essential amino acids according to the current Danish recommendations. Materials and Methods The experiment was carried out in a commercial 1800-sow herd (Lemvig, Denmark). The study conformed with Danish laws and regulations for the humane care and use of animals in research (The Danish Ministry of Justice, 1995) and the research protocols were approved by the Danish Animal Experimentation Inspectorate. Experimental Design, Housing, and Management A dose-response study including 6 dietary treatments increasing in SID Lys was designed to determine the minimum dietary SID Lys level required to maximize litter gain and minimize sow BW loss. A total of 396 parity 1 to 5 crossbred sows (Danish Landrace × Danish Yorkshire, DanBred, Herlev, Denmark) were included. All sows in the herd were mated with DanBred Duroc semen (Ornestation Mors, Redsted, Denmark). For 22 consecutive weeks at 7 d before expected farrowing, a block of 18 sows (3 sows per dietary treatment, stratified for parity) were randomly allocated in a complete block design to 1 of 6 dietary treatments. Sows were placed at random in individual farrowing crates within a room. The distribution of parities (27%, 23%, 21%, 16%, and 13% of first to fifth parity, respectively) was similar in all 6 dietary treatments and the average parity in each treatment was 2.6 ± 0.1. Litters were standardized at day 3 ± 2 postpartum to 14 piglets. The average BW of each piglet was at litter standardization 1.74 ± 0.02 kg. The herd had 6 farrowing rooms and a block of 18 sows were moved into one of these rooms each week starting in September 2017 and ending in February 2018. Each crate was equipped with a covered creep area and an infrared censored heating lamp (VengSystem A/S, Roslev, Denmark) that gradually decreased the temperature from 34 °C at farrowing to 22 °C 15 d after farrowing. The room temperature was maintained constant at 20 °C and the air was ventilated through wall inlets using negative pressure ventilation. Besides the appearance of natural light, artificial light was turned on from 0630 to 1530 h. The sows and piglets were managed, treated, and vaccinated by the stock personnel according to the normal routines in the herd. On days 3 or 4 after farrowing, all piglets were tail docked and given iron injection (0.5 mL; Solofer Vet., Pharmacosmos A/S, Holbæk, Denmark), and male piglets were castrated surgically using postoperative analgesia (0.1 mL; Melovem, Dopharma B.V., VX Raamsdonksveer, The Netherlands). Furthermore, iron was provided throughout the whole lactation period to the piglets as oral supplement through the water from a drinking nipple in the pen (1%; Opti-Jern, R2 Agro A/S, Hedensted, Denmark). Dietary Treatments Two diets (a low-Lys and a high-Lys diet; Table 1) were formulated and mixed in different proportions to obtain 6 dietary treatments with increased SID Lys content (Table 2). The low- and high-Lys diets were mainly based on barley, wheat, oats, soybean meal, and sugar beet pulp. The average SID Lys content of dietary treatment 1 through 6 provided for the sows were 6.19, 6.90, 7.63, 8.33, 9.04, and 9.76 g/kg as-fed. Based on the Danish recommendations, the low-Lys diet (diet 1) was deficient in Lys, whereas the high-Lys diet (diet 6) was in excess of the recommended Lys concentration (8.32 g/kg of SID Lys; Table 3; Tybirk et al. 2017). The 6 dietary treatments were formulated to contain identical and adequate levels (≥102%) of SID Met, Met + Cys, Thr, Trp, Ile, Leu, His, Phe, Phe + Tyr, and Val per NE basis according to the current Danish recommendations (Tybirk et al., 2017). The diets were isoenergetic based on the Danish feed evaluation system (Danish Feed Units) which is a potential physiological energy system closely related to the NE system (Patience, 2012). The slight increase in SID CP from diet 1 (129 g/kg) through diet 6 (133 g/kg) was due to the addition of crystalline Lys, because the contents of the other essential amino acids were kept constant across the treatments. Table 1. Ingredient composition of the low-Lys and high-Lys diets Diets1 Low-Lys High-Lys Ingredient, g/kg “as-fed”  Barley 350 350  Wheat 350 344  Oat 50.0 50.0  Soybean meal, dehulled 167 167  Sugar beet pulp 20.0 20.0  Leci E Basic2 15.0 15.0  Palm oil 13.1 12.8  L-Lys 0.19 5.69  DL-Met 0.79 0.80  L-Thr 1.10 1.10  Monocalcium phosphate 9.5 9.5  Limestone 12.7 12.6  Salt 4.9 4.9  Cholin Extra3 0.15 0.15  Levucell SB 10 ME Titan4 0.10 0.10  Vitamin and mineral premix5 6.1 6.1 Diets1 Low-Lys High-Lys Ingredient, g/kg “as-fed”  Barley 350 350  Wheat 350 344  Oat 50.0 50.0  Soybean meal, dehulled 167 167  Sugar beet pulp 20.0 20.0  Leci E Basic2 15.0 15.0  Palm oil 13.1 12.8  L-Lys 0.19 5.69  DL-Met 0.79 0.80  L-Thr 1.10 1.10  Monocalcium phosphate 9.5 9.5  Limestone 12.7 12.6  Salt 4.9 4.9  Cholin Extra3 0.15 0.15  Levucell SB 10 ME Titan4 0.10 0.10  Vitamin and mineral premix5 6.1 6.1 1Diets represent the 2 extreme diets corresponding to treatment 1 and 6, whereas the 4 other diets were created by mixing these 2 in different proportions, cf. Table 2. 2Leci E Basic is a lecithin-rich oil composed of phospholipids, free fatty acids, and triglycerides from rapeseed oil (Evilec ApS, Kolding, Denmark). 3Cholin Extra is an herbal feed ingredient containing choline in a natural and bioavailable conjugated form without the risk of chemical reactions with vitamins (Agilia A/S, Videbæk, Denmark). 4Levucell SB 10 ME Titan (Lallemand Animal Nutrition, Toulouse, France) is an active dry yeast probiotic containing the yeast Saccharomyces cerevisiae CNCM I-1079 1.0 × 1010 cfu/g. 5Provided the following amounts of minerals and vitamins per kg diet: 12,000 IU vitamin A; 2,000 IU 25-hydroxy vitamin D3 (HyD, DSM Nutritional Products, Basel, Switzerland); 270 mg DL-alfatocoferol; 2.40 mg vitamin B1; 8.94 mg vitamin B2; 5.57 mg vitamin B6; 0.04 mg vitamin B12; 26.88 mg D-pantothenic acid; 33.78 mg niacin; 5.28 mg folic acid; 86.00 mg iron (FeSO4); 60.00 mg iron fumerate; 15.00 mg copper (CuSO4); 50.00 mg manganese (MnO); 2.00 mg iodine (Ca(IO3)2); 0.25 mg selenium (Na2SeO3); 50.00 mg zinc sulphate (ZnSO4); 50.00 mg zinc chelated; 0.15 mg selenium chelated. Furthermore, Ronozyme HiPhos GT provided 1,000 phytase activity (FTU) per kg of diet (DSM Nutritional Products, Basel, Switzerland). Open in new tab Table 1. Ingredient composition of the low-Lys and high-Lys diets Diets1 Low-Lys High-Lys Ingredient, g/kg “as-fed”  Barley 350 350  Wheat 350 344  Oat 50.0 50.0  Soybean meal, dehulled 167 167  Sugar beet pulp 20.0 20.0  Leci E Basic2 15.0 15.0  Palm oil 13.1 12.8  L-Lys 0.19 5.69  DL-Met 0.79 0.80  L-Thr 1.10 1.10  Monocalcium phosphate 9.5 9.5  Limestone 12.7 12.6  Salt 4.9 4.9  Cholin Extra3 0.15 0.15  Levucell SB 10 ME Titan4 0.10 0.10  Vitamin and mineral premix5 6.1 6.1 Diets1 Low-Lys High-Lys Ingredient, g/kg “as-fed”  Barley 350 350  Wheat 350 344  Oat 50.0 50.0  Soybean meal, dehulled 167 167  Sugar beet pulp 20.0 20.0  Leci E Basic2 15.0 15.0  Palm oil 13.1 12.8  L-Lys 0.19 5.69  DL-Met 0.79 0.80  L-Thr 1.10 1.10  Monocalcium phosphate 9.5 9.5  Limestone 12.7 12.6  Salt 4.9 4.9  Cholin Extra3 0.15 0.15  Levucell SB 10 ME Titan4 0.10 0.10  Vitamin and mineral premix5 6.1 6.1 1Diets represent the 2 extreme diets corresponding to treatment 1 and 6, whereas the 4 other diets were created by mixing these 2 in different proportions, cf. Table 2. 2Leci E Basic is a lecithin-rich oil composed of phospholipids, free fatty acids, and triglycerides from rapeseed oil (Evilec ApS, Kolding, Denmark). 3Cholin Extra is an herbal feed ingredient containing choline in a natural and bioavailable conjugated form without the risk of chemical reactions with vitamins (Agilia A/S, Videbæk, Denmark). 4Levucell SB 10 ME Titan (Lallemand Animal Nutrition, Toulouse, France) is an active dry yeast probiotic containing the yeast Saccharomyces cerevisiae CNCM I-1079 1.0 × 1010 cfu/g. 5Provided the following amounts of minerals and vitamins per kg diet: 12,000 IU vitamin A; 2,000 IU 25-hydroxy vitamin D3 (HyD, DSM Nutritional Products, Basel, Switzerland); 270 mg DL-alfatocoferol; 2.40 mg vitamin B1; 8.94 mg vitamin B2; 5.57 mg vitamin B6; 0.04 mg vitamin B12; 26.88 mg D-pantothenic acid; 33.78 mg niacin; 5.28 mg folic acid; 86.00 mg iron (FeSO4); 60.00 mg iron fumerate; 15.00 mg copper (CuSO4); 50.00 mg manganese (MnO); 2.00 mg iodine (Ca(IO3)2); 0.25 mg selenium (Na2SeO3); 50.00 mg zinc sulphate (ZnSO4); 50.00 mg zinc chelated; 0.15 mg selenium chelated. Furthermore, Ronozyme HiPhos GT provided 1,000 phytase activity (FTU) per kg of diet (DSM Nutritional Products, Basel, Switzerland). Open in new tab Table 2. Analyzed nutrient composition of the 6 dietary treatments (as-fed)1 Dietary treatments2 1 2 3 4 5 6 Proportions, %  Low-Lys 100 80 60 40 20 0  High-Lys 0 20 40 60 80 100 Chemical composition, g/kg  DM 874 874 874 874 874 874  Fat 47.4 47.3 47.4 47.4 47.5 47.5  Ash 48.8 48.8 48.9 49.0 49.1 49.3  Calcium 9.18 9.05 8.95 8.88 8.82 8.77  Phosphorous 5.85 5.79 5.75 5.75 5.73 5.73  Energy, Danish Feed Units/kg3 1.09 1.09 1.09 1.09 1.09 1.09  Energy, MJ ME/kg 14.04 14.04 14.04 14.04 14.04 14.04 Protein and amino acids, g/kg  CP 154 154 155 156 156 157  Lys 7.25 7.94 8.66 9.35 10.05 10.76  Met 2.74 2.74 2.76 2.77 2.78 2.79  Met + Cys 5.41 5.40 5.41 5.41 5.40 5.41  Thr 6.05 6.04 6.03 6.03 6.02 6.02  Trp 2.02 2.02 2.02 2.01 2.01 2.01  Ile 5.66 5.64 5.63 5.62 5.60 5.59  Leu 10.49 10.46 10.45 10.41 10.38 10.37  His 3.58 3.57 3.57 3.56 3.54 3.54  Phe 7.14 7.13 7.11 7.09 7.06 7.03  Phe + Tyr 12.67 12.65 12.64 12.61 12.58 12.56  Val 6.75 6.74 6.74 6.72 6.71 6.70 Digestible protein and amino acids, g/kg4  SID CP 129 130 131 132 132 133  SID Lys 6.19 6.90 7.63 8.33 9.04 9.76  SID Met 2.49 2.50 2.51 2.52 2.53 2.55  SID Met + Cys 4.68 4.68 4.69 4.70 4.70 4.72  SID Thr 5.13 5.12 5.12 5.11 5.10 5.10  SID Trp 1.73 1.73 1.73 1.72 1.72 1.72  SID Ile 4.83 4.81 4.81 4.79 4.78 4.77  SID Leu 9.08 9.05 9.04 9.01 8.99 8.98  SID His 3.03 3.02 3.01 3.00 2.99 2.99  SID Phe 6.27 6.26 6.25 6.22 6.20 6.18  SID Phe + Tyr 11.03 11.01 11.00 10.98 10.95 10.94  SID Val 5.68 5.67 5.66 5.65 5.64 5.64 Dietary treatments2 1 2 3 4 5 6 Proportions, %  Low-Lys 100 80 60 40 20 0  High-Lys 0 20 40 60 80 100 Chemical composition, g/kg  DM 874 874 874 874 874 874  Fat 47.4 47.3 47.4 47.4 47.5 47.5  Ash 48.8 48.8 48.9 49.0 49.1 49.3  Calcium 9.18 9.05 8.95 8.88 8.82 8.77  Phosphorous 5.85 5.79 5.75 5.75 5.73 5.73  Energy, Danish Feed Units/kg3 1.09 1.09 1.09 1.09 1.09 1.09  Energy, MJ ME/kg 14.04 14.04 14.04 14.04 14.04 14.04 Protein and amino acids, g/kg  CP 154 154 155 156 156 157  Lys 7.25 7.94 8.66 9.35 10.05 10.76  Met 2.74 2.74 2.76 2.77 2.78 2.79  Met + Cys 5.41 5.40 5.41 5.41 5.40 5.41  Thr 6.05 6.04 6.03 6.03 6.02 6.02  Trp 2.02 2.02 2.02 2.01 2.01 2.01  Ile 5.66 5.64 5.63 5.62 5.60 5.59  Leu 10.49 10.46 10.45 10.41 10.38 10.37  His 3.58 3.57 3.57 3.56 3.54 3.54  Phe 7.14 7.13 7.11 7.09 7.06 7.03  Phe + Tyr 12.67 12.65 12.64 12.61 12.58 12.56  Val 6.75 6.74 6.74 6.72 6.71 6.70 Digestible protein and amino acids, g/kg4  SID CP 129 130 131 132 132 133  SID Lys 6.19 6.90 7.63 8.33 9.04 9.76  SID Met 2.49 2.50 2.51 2.52 2.53 2.55  SID Met + Cys 4.68 4.68 4.69 4.70 4.70 4.72  SID Thr 5.13 5.12 5.12 5.11 5.10 5.10  SID Trp 1.73 1.73 1.73 1.72 1.72 1.72  SID Ile 4.83 4.81 4.81 4.79 4.78 4.77  SID Leu 9.08 9.05 9.04 9.01 8.99 8.98  SID His 3.03 3.02 3.01 3.00 2.99 2.99  SID Phe 6.27 6.26 6.25 6.22 6.20 6.18  SID Phe + Tyr 11.03 11.01 11.00 10.98 10.95 10.94  SID Val 5.68 5.67 5.66 5.65 5.64 5.64 1Average values of the analyzed content of the 4 batches of the low-Lys diet (treatment 1) and the high-Lys diet (treatment 6), respectively. Treatment 2 through 5 was calculated based on inclusion level of the low-Lys and high-Lys diet. 2Diets were fed to sows from the day after farrowing (day 1) until weaning (day 26 ± 3). 3Danish Feed Units are potential physiological energy closely related to NE (Patience, 2012). 4SID = standardized ileal digestible. The content of SID CP and amino acids were calculated based on analyzed total values, inclusion level of treatment 1 and 6, and on SID digestibility coefficients (Pedersen and Boisen, 2002) of the feed ingredients. Open in new tab Table 2. Analyzed nutrient composition of the 6 dietary treatments (as-fed)1 Dietary treatments2 1 2 3 4 5 6 Proportions, %  Low-Lys 100 80 60 40 20 0  High-Lys 0 20 40 60 80 100 Chemical composition, g/kg  DM 874 874 874 874 874 874  Fat 47.4 47.3 47.4 47.4 47.5 47.5  Ash 48.8 48.8 48.9 49.0 49.1 49.3  Calcium 9.18 9.05 8.95 8.88 8.82 8.77  Phosphorous 5.85 5.79 5.75 5.75 5.73 5.73  Energy, Danish Feed Units/kg3 1.09 1.09 1.09 1.09 1.09 1.09  Energy, MJ ME/kg 14.04 14.04 14.04 14.04 14.04 14.04 Protein and amino acids, g/kg  CP 154 154 155 156 156 157  Lys 7.25 7.94 8.66 9.35 10.05 10.76  Met 2.74 2.74 2.76 2.77 2.78 2.79  Met + Cys 5.41 5.40 5.41 5.41 5.40 5.41  Thr 6.05 6.04 6.03 6.03 6.02 6.02  Trp 2.02 2.02 2.02 2.01 2.01 2.01  Ile 5.66 5.64 5.63 5.62 5.60 5.59  Leu 10.49 10.46 10.45 10.41 10.38 10.37  His 3.58 3.57 3.57 3.56 3.54 3.54  Phe 7.14 7.13 7.11 7.09 7.06 7.03  Phe + Tyr 12.67 12.65 12.64 12.61 12.58 12.56  Val 6.75 6.74 6.74 6.72 6.71 6.70 Digestible protein and amino acids, g/kg4  SID CP 129 130 131 132 132 133  SID Lys 6.19 6.90 7.63 8.33 9.04 9.76  SID Met 2.49 2.50 2.51 2.52 2.53 2.55  SID Met + Cys 4.68 4.68 4.69 4.70 4.70 4.72  SID Thr 5.13 5.12 5.12 5.11 5.10 5.10  SID Trp 1.73 1.73 1.73 1.72 1.72 1.72  SID Ile 4.83 4.81 4.81 4.79 4.78 4.77  SID Leu 9.08 9.05 9.04 9.01 8.99 8.98  SID His 3.03 3.02 3.01 3.00 2.99 2.99  SID Phe 6.27 6.26 6.25 6.22 6.20 6.18  SID Phe + Tyr 11.03 11.01 11.00 10.98 10.95 10.94  SID Val 5.68 5.67 5.66 5.65 5.64 5.64 Dietary treatments2 1 2 3 4 5 6 Proportions, %  Low-Lys 100 80 60 40 20 0  High-Lys 0 20 40 60 80 100 Chemical composition, g/kg  DM 874 874 874 874 874 874  Fat 47.4 47.3 47.4 47.4 47.5 47.5  Ash 48.8 48.8 48.9 49.0 49.1 49.3  Calcium 9.18 9.05 8.95 8.88 8.82 8.77  Phosphorous 5.85 5.79 5.75 5.75 5.73 5.73  Energy, Danish Feed Units/kg3 1.09 1.09 1.09 1.09 1.09 1.09  Energy, MJ ME/kg 14.04 14.04 14.04 14.04 14.04 14.04 Protein and amino acids, g/kg  CP 154 154 155 156 156 157  Lys 7.25 7.94 8.66 9.35 10.05 10.76  Met 2.74 2.74 2.76 2.77 2.78 2.79  Met + Cys 5.41 5.40 5.41 5.41 5.40 5.41  Thr 6.05 6.04 6.03 6.03 6.02 6.02  Trp 2.02 2.02 2.02 2.01 2.01 2.01  Ile 5.66 5.64 5.63 5.62 5.60 5.59  Leu 10.49 10.46 10.45 10.41 10.38 10.37  His 3.58 3.57 3.57 3.56 3.54 3.54  Phe 7.14 7.13 7.11 7.09 7.06 7.03  Phe + Tyr 12.67 12.65 12.64 12.61 12.58 12.56  Val 6.75 6.74 6.74 6.72 6.71 6.70 Digestible protein and amino acids, g/kg4  SID CP 129 130 131 132 132 133  SID Lys 6.19 6.90 7.63 8.33 9.04 9.76  SID Met 2.49 2.50 2.51 2.52 2.53 2.55  SID Met + Cys 4.68 4.68 4.69 4.70 4.70 4.72  SID Thr 5.13 5.12 5.12 5.11 5.10 5.10  SID Trp 1.73 1.73 1.73 1.72 1.72 1.72  SID Ile 4.83 4.81 4.81 4.79 4.78 4.77  SID Leu 9.08 9.05 9.04 9.01 8.99 8.98  SID His 3.03 3.02 3.01 3.00 2.99 2.99  SID Phe 6.27 6.26 6.25 6.22 6.20 6.18  SID Phe + Tyr 11.03 11.01 11.00 10.98 10.95 10.94  SID Val 5.68 5.67 5.66 5.65 5.64 5.64 1Average values of the analyzed content of the 4 batches of the low-Lys diet (treatment 1) and the high-Lys diet (treatment 6), respectively. Treatment 2 through 5 was calculated based on inclusion level of the low-Lys and high-Lys diet. 2Diets were fed to sows from the day after farrowing (day 1) until weaning (day 26 ± 3). 3Danish Feed Units are potential physiological energy closely related to NE (Patience, 2012). 4SID = standardized ileal digestible. The content of SID CP and amino acids were calculated based on analyzed total values, inclusion level of treatment 1 and 6, and on SID digestibility coefficients (Pedersen and Boisen, 2002) of the feed ingredients. Open in new tab Table 3. Actual dietary concentrations of protein and amino acids relative to Danish recommendations Dietary treatments, %2 Danish recommendations, g/kg1 1 2 3 4 5 6 SID CP 127 102 102 103 103 104 104 SID Lys 8.32 74 83 92 100 109 117 SID Met 2.59 96 96 97 97 98 98 SID Met + Cys 4.86 96 96 97 97 97 97 SID Thr 5.40 95 95 95 95 94 94 SID Trp 1.66 104 104 104 103 103 103 SID Ile 4.64 104 104 104 103 103 103 SID Leu 8.96 101 101 101 101 100 100 SID His 3.02 100 100 100 99 99 99 SID Phe 4.54 138 138 138 137 137 136 SID Phe + Tyr 9.40 117 117 117 117 117 116 SID Val 5.72 99 99 99 99 99 99 Dietary treatments, %2 Danish recommendations, g/kg1 1 2 3 4 5 6 SID CP 127 102 102 103 103 104 104 SID Lys 8.32 74 83 92 100 109 117 SID Met 2.59 96 96 97 97 98 98 SID Met + Cys 4.86 96 96 97 97 97 97 SID Thr 5.40 95 95 95 95 94 94 SID Trp 1.66 104 104 104 103 103 103 SID Ile 4.64 104 104 104 103 103 103 SID Leu 8.96 101 101 101 101 100 100 SID His 3.02 100 100 100 99 99 99 SID Phe 4.54 138 138 138 137 137 136 SID Phe + Tyr 9.40 117 117 117 117 117 116 SID Val 5.72 99 99 99 99 99 99 1Tybirk et al. (2017). 2Actual dietary concentrations relative to the Danish recommendations given in %. Highlighted in bold are the concentrations that were fed below the recommended level. Underlined is the most limiting amino acid within each dietary treatment. Open in new tab Table 3. Actual dietary concentrations of protein and amino acids relative to Danish recommendations Dietary treatments, %2 Danish recommendations, g/kg1 1 2 3 4 5 6 SID CP 127 102 102 103 103 104 104 SID Lys 8.32 74 83 92 100 109 117 SID Met 2.59 96 96 97 97 98 98 SID Met + Cys 4.86 96 96 97 97 97 97 SID Thr 5.40 95 95 95 95 94 94 SID Trp 1.66 104 104 104 103 103 103 SID Ile 4.64 104 104 104 103 103 103 SID Leu 8.96 101 101 101 101 100 100 SID His 3.02 100 100 100 99 99 99 SID Phe 4.54 138 138 138 137 137 136 SID Phe + Tyr 9.40 117 117 117 117 117 116 SID Val 5.72 99 99 99 99 99 99 Dietary treatments, %2 Danish recommendations, g/kg1 1 2 3 4 5 6 SID CP 127 102 102 103 103 104 104 SID Lys 8.32 74 83 92 100 109 117 SID Met 2.59 96 96 97 97 98 98 SID Met + Cys 4.86 96 96 97 97 97 97 SID Thr 5.40 95 95 95 95 94 94 SID Trp 1.66 104 104 104 103 103 103 SID Ile 4.64 104 104 104 103 103 103 SID Leu 8.96 101 101 101 101 100 100 SID His 3.02 100 100 100 99 99 99 SID Phe 4.54 138 138 138 137 137 136 SID Phe + Tyr 9.40 117 117 117 117 117 116 SID Val 5.72 99 99 99 99 99 99 1Tybirk et al. (2017). 2Actual dietary concentrations relative to the Danish recommendations given in %. Highlighted in bold are the concentrations that were fed below the recommended level. Underlined is the most limiting amino acid within each dietary treatment. Open in new tab Feeding and Feeding System Sows received their dietary treatments from the day after farrowing (day 1) to weaning at day 26 ± 3. Throughout this period, sows were fed 3 equally sized meals daily between 0430 and 0930 h, 1130 and 1630 h, and 1930 and 0030 h in 7-, 8-, and 9-h intervals, respectively. Primiparous sows were assigned to one feed curve and multiparous sows were assigned to another feed curve; at day 1, the total feed supply was 2.3 kg/d and it was progressively increased until day 17 of lactation to a maximum of 7.5 kg/d for primiparous sows and 8.4 kg/d for multiparous sows. The fixed feed curves prevented primi- and multiparous sows from compensating the planned dietary Lys undersupply by increasing their ADFI (most pronounced for sows fed diet 1). The feed curves targeted for and ADFI throughout lactation of 6.15 and 6.82 kg for primi- and multiparous sows, respectively. Once daily, the feed curve was adjusted on an individual basis allowing for reductions in feed supply. In case of feed residues, the feed supply for the next 3 meals was reduced to ensure that sows ate all the feed they were provided. Feed residues were not weighed, but due to the individual daily adjustments, sows ate in general their daily ration (i.e., it was assumed that the feed supply was equal to ADFI). Besides water being freely available to sows, a portion of water was added at each meal just before the feed reached the trough. Sows were fed by a SpotMix feeding system (Schauer Agrotronic, Prambachkirchen, Austria) using air-assisted transport. This avoided mixing of feed residues from previous feedings in the pipes. The feeding system allowed usage of individual feed curves which ensured precise mixing and weighing of the low- and high-Lys diets to target the right proportion of the 2 diets fed to individual sows at each meal. Precision of the feeding system in terms of mixing of the diets and amount supplied was verified on a monthly basis by weighing a portion of feed delivered to a random trough and by analyzing spot samples of the low- and high-Lys diets. Furthermore, colored micro grits (0.05%; Jadis Additiva, Schiedam, The Netherlands) were added to the 2 diets to check whether the right feed was delivered from the right silos. Feed Manufacturing and Analysis The low- and high-Lys diets were manufactured (Vestjyllands Andel, Hee, Denmark) 4 times throughout the experimental period with approximately 6-wk intervals. At each manufacturing, 10-kg samples were taken of each diet during the manufacturing process. Subsequently, each sample was split into subsamples using a 32-slot riffle sample divider (Rationel Kornservice, Esbjerg, Denmark). In total, 4 subsamples per produced batch of low- and high-Lys diet, respectively, were analyzed in duplicates at a commercial feed testing laboratory (Eurofins Steins Laboratory A/S, Vejen, Denmark). All feed analyses were performed according to the European Commission Directives [EC] 64/1998 and [EC] 152/2009, respectively. Digestibility coefficients for nutrients (Pedersen and Boisen, 2002) in each ingredient were used to calculate SID coefficients for each nutrient within the low- and high-Lys diets. These SID coefficients were applied to the total analyzed nutritive values of the low- and high-Lys diets to calculate their SID nutrient composition. Based on registrations of daily feed supply of the low- and high-Lys diets for the individual sow, and the calculated SID nutrient composition of the 4 batches of the 2 diets, the actual nutrient composition was calculated for each meal fed to individual sows which formed the basis for calculating the average chemical composition of dietary treatment 1 through 6 provided for the experimental sows (Table 2). Data Collection and Chemical Analysis At litter standardization (day 3 ± 2 d after farrowing) and at weaning (day 26 ± 3 d after farrowing), referred to as 3 and 26 days in milk (DIM), respectively, BW of the sows was measured by a walk-in scale (Bjerringbro Vægte ApS, Bjerringbro, Denmark), and the P2 site back fat (BF) thickness of the sows was measured by ultrasonography using a Sono-Grader II (Renco Corporation, Minneapolis, MN). Litter weight was recorded at 3 and 26 DIM by a weight trolley (Bjerringbro Vægte ApS, Bjerringbro, Denmark). Weaning-to-estrus interval (WEI) and total born piglets were registered in the following reproductive cycle. On a subsample of 72 parity 2 to 4 sows, additional measurements were collected. Besides, at 3 and 26 DIM, litter weight was also recorded at 10 and 17 DIM (±3 d). Furthermore, milk and blood were sampled from the sows at 3 ± 2 DIM, and at 10, 17, and 24 DIM (±3 d). After removal of the litter for minimum 30 min, intramuscular administration of 2 mL oxytocin (10 IU/mL; Intervet Danmark A/S, Ballerup, Denmark) induced the sows to facilitate milk letdown and 60 mL milk was sampled manually from 4 to 5 front and rear teats on both udder halves. The milk was filtered through gauze and stored at −20 °C until analysis for the content of DM, lactose, fat, true protein, casein, and urea by infrared spectroscopy (MilkoScan 4000, Foss Electric, Hillerød, Denmark). The blood samples were drawn from the jugular vein 4 ± 1 h after feeding into sodium heparin vacutainer tubes (9 mL Vacuette NH Sodium Heparin; Greiner Bio One International GmbH, Kremsmünster, Austria). Immediately after, the samples were put on ice until centrifugation at 1,558 × g for 12 min at 4 °C and plasma was harvested and stored at −20 °C until analysis. Before analysis, the plasma samples were thawed at room temperature (20 °C) and the content of plasma urea nitrogen (PUN), creatinine, NEFA, triacylglycerol (TAG), glucose, and lactate were determined by spectrophotometry according to standard procedures (ADVIA 1800 Clinical Chemistry System, Siemens Healthcare A/S, Ballerup, Denmark). Deuterium oxide (D2O) dilution space was measured as described by Theil et al. (2002) at 3 and 26 DIM to derive the body water, fat, ash, and protein content. An initial blood sample was drawn from the jugular vein before intramuscular administration of a 40% D2O solution in the neck (0.0425 g per kg BW) to determine the background level of D2O in the individual sow. Besides, the weight of the full syringe, the weight before and after injection was registered to determine the exact amount of D2O solution injected. Another blood sample was collected 6 ± 1 h after injection when D2O was equilibrated with body water (Pedersen, 2019). The blood samples were centrifuged at 1,558 × g for 12 min at 4 °C, and plasma was harvested and stored at −20 °C until analysis. Calculations and Statistical Analyses Average daily gain of the litter was calculated as the difference between litter weight at standardization and weaning including weights of dead piglets or piglets removed from the litter in the experimental period, divided by number of suckling days. The daily milk yield was estimated based on litter growth and litter size as described by Hansen et al. (2012). The gross energy of milk was estimated, using the equation assigned by Chwalibog (2006): GE (MJ/kg) = (38.9, MJ/kg × milk fat, % + 23.8, MJ/kg × milk protein, % + 16.3, MJ/kg × lactose, %)/100%. Body pools of protein and fat at 3 ± 2 and 26 ± 3 DIM were estimated from D2O dilution space, BF measurements, and BW according to prediction equations developed for Landrace × Yorkshire gilts reported by Rozeboom et al. (1994). All statistical analyses were conducted using SAS Enterprise Guide 7.1 (SAS Inst. Inc., Cary, NC). For the 396-sow study, the following model was used to analyze the response variables: Yijk=μ+αi+βj+νk+εijk, (1) in which Yijk is the response variable, µ is the overall mean, α i is the fixed effect of dietary treatment (Trt) (i = 1,…, 6), β j is the fixed effect of parity (j = primi or multi), ν k is the random effect of block (k = 1, 2,…, 22) with sow as the experimental unit, and ε ijk is the random error component, which was assumed to be N(0, σ 2). For analysis of sow BF loss and litter ADG, initial measures of BF and litter weight were included as covariates, respectively. The skewed frequency of primi- and multiparous sows (27% and 73%, respectively) in the experiment were accounted for using the LSMEANS OBSMARGINS option to specify that these 2 classes were not equally distributed and hence the least squared means were estimated according to this. The parity × Trt interaction was tested but was not significant (P > 0.05) and consequently not included in the final model. For the subsample of sows (n = 72), plasma metabolites, milk composition, and ADG of litter were analyzed as repeated measurements to account for weekly recordings using the following model: Yijkl= μ+αi+βj+αβij+γDjl+νk+ωjl+εijkl, (2) in which Yijkl is the response variable, µ is the overall mean, α i is the fixed effect of Trt (i = 1,…, 6), β j is the fixed effect of DIM (j = 3, 10, 17, 24), αβ ij is the interaction term between Trt and DIM, γDjl is a covariate to account for the actual day in milk (day ranging from −3 to +3) for the lth sow (l = 1, 2,…, 72) within jth DIM, ν k is the random effect of block (k = 6, 7,…, 11), ω jl is the random effect of the lth sow in the jth DIM, and ε ijkl is the random error component which was assumed to be N (0, σ 2). When analyzing body pools and changes in body pools of protein and fat, Eq. 2 without β j was used. Litter weight at standardization was used as a covariate when analyzing litter ADG. When analyzing changes in body protein and fat pools, sow BW at standardization was used as a covariate. Data on plasma NEFA and lactate were log-transformed to make data conform to variance homogeneity. Most variables were subjected to ANOVA using the MIXED procedure of SAS. However, farrowing rate was considered a binomial response and was analyzed using a logistic regression fit by PROC GLIMMIX of SAS. Results on normally distributed data are given as least squared means and the greatest SEM values within diets or within DIM are reported. Results on log-transformed data are given as back-transformed estimates and the 95% confidence intervals. Results on farrowing rate are given as means and the 95% confidence intervals. Results were considered significant at P < 0.05. When results are considered significant, the Tukey–Kramer test was used in pairwise comparisons of means adjusting the P-values. Orthogonal polynomial contrasts were used to partition linear and quadratic effects of dietary SID Lys. Coefficients of the orthogonal polynomial contrasts were generated by the IML procedure of SAS using actual means of SID Lys per kg feed for each Trt. Statistical significance was acknowledged at P < 0.05 and trends at 0.05 ≤ P ≤ 0.10. The dietary SID Lys required to maximize litter ADG and minimize sow BW loss was estimated by applying linear and quadratic broken-line models using the NLMIXED procedure of SAS as described by Robbins et al. (2006) and Goncalves et al. (2016). In addition, linear and quadratic broken-line models were fitted to other traits showing linear or quadratic significant effects or tendencies of dietary SID Lys and/or Trt × DIM interactions. Based on recordings of the daily feed supplies for the individual sow, chemical analysis of the low-Lys and high-Lys diets, and digestibility coefficients of Lys for the diets, an average dietary SID Lys concentration was calculated for the individual sow and used as the explanatory variable. The linear broken-line model consists of 2-line segments: a line with a slope different from zero and a plateau or 2 lines each having a slope different from zero. The model for SID Lys levels smaller than the breakpoint (Xi < ω) is as follows: Yij=φ+β×(ω Xi)+bj+εij. (3) The model for SID Lys levels greater than the breakpoint (Xi > ω) is as follows: Yij=φ+β×(Xiω)+bj+εij (4) When a plateau was located at Xi ≥ ω, (ω − Xi) is defined as zero, whereas (Xi − ω) is defined as zero when a plateau was located at Xi≤ ω. Differently from Eqs. 3 and 4, the quadratic broken-line model has either (ω − Xi) or (Xi − ω) squared, depending on whether a plateau was located below or above the breakpoint. Yij is the response of the ith sow, within the jth block, Xi is the concentration of SID Lys in g/kg feed to the individual sow, φ is the horizontal asymptote of the breakpoint (maximum/minimum response), β is the slope for the increasing or decreasing line segment having values of Xi smaller or greater than the breakpoint, ω is the breakpoint of SID Lys in g/kg feed, bj is the random effect of block (j = 1, 2,…., 22 for the 396-sow data set or 6, 7,…, 11 for the 72-sow data set) being N(0,σb2) ⁠, and ε ij is the random error associated with the ith sow in the jth block. When there was a significant effect of parity (primi vs. multi) or DIM, the fixed effect of parity or DIM was incorporated both in β and ω. The output of the statistical models was compared according to the following criteria and only the best fitting model, if any converged, was presented in the results: 1) Akaike information criteria and −2 log likelihood fit statistics were used to compare nested models, where smaller values indicate a better fit to data, 2) the P-value for the slope of one of the line segments below/above the breakpoint should be different from zero to define a breakpoint in the nonlinear mixed model, where P-values below 0.15 were accepted, 3) estimated breakpoints should be within the tested range of dietary SID Lys concentrations, and 4) careful evaluation of the graphical output was considered as well (Robbins et al., 2006). Results Litter Characteristics and Sow Performance Six of the included sows were removed from the experiment before weaning due to postpartum dysgalactia syndrome and were therefore left out of the data set. Weaning litter size (13.0 ± 0.1; Table 4) was similar between the 6 dietary treatments (P = 0.28). According to results of the linear broken-line model for litter ADG (day 3 to 26), there was no difference between primi- and multiparous sows in dietary SID Lys required to maximize litter gain (P = 0.35) and the estimated requirement was 8.11 ± 0.66 g/kg of SID Lys (Fig. 1). Litter ADG differed between primi- and multiparous sows (P < 0.001) and reached a plateau at 2.93 and 3.36 kg/d, respectively (P < 0.05). Average daily litter gain increased from early to peak lactation (P < 0.001; Fig. 2). Table 4. Effect of increasing standardized ileal digestible (SID) Lys on sow and litter performance, and subsequent reproduction (n = 390)1 Dietary treatment, SID Lys g/kg2 6.19 6.90 7.63 8.33 9.04 9.76 Parity P-value3,4 Item 1 2 3 4 5 6 SEM Primi Multi SEM Trt Parity Lin Quad n 65 64 66 66 63 66 106 284 Sows  Parity 2.6 2.7 2.6 2.6 2.7 2.7 0.19 1.00 NS NS  Days in milk, d 26 26 26 26 25 26 0.14 26.4 25.3 0.11 0.83 <0.001 NS NS  ADFI, kg 6.36 6.44 6.46 6.48 6.48 6.47 0.05 5.88 6.66 0.04 0.32 <0.001 * NS  SID protein intake, g/d 824b 838ab 845ab 853a 857a 861a 6.20 772 874 5.13 <0.001 <0.001 *** NS  SID Lys intake, g/d 39.4f 44.2e 48.8d 53.5c 58.1b 63.9a 0.46 46.9 53.0 0.39 <0.001 <0.001 *** NS  Sow BW day 3, kg 249 250 245 251 247 248 3.39 206 264 2.90 0.79 <0.001 NS NS  BW loss (day 3 to 26), kg/d 0.54a 0.38ab 0.38ab 0.32ab 0.15b 0.16b 0.06 0.37 0.31 0.05 <0.001 0.20 *** NS  Sow BF day 3, mm 16.2ab 16.1ab 15.6b 17.0a 16.0ab 15.1b 0.38 15.2 16.3 0.31 <0.01 <0.01 NS †  BF loss (day 3 to 26), mm/d 0.16 0.15 0.16 0.17 0.16 0.15 0.01 0.17 0.15 0.01 0.29 <0.01 NS † Piglets  Litter size day 3 14.0 14.0 14.0 14.0 14.0 14.0 – 14.0 14.0 – – – – –  Litter size day 26 13.1 12.8 13.0 13.1 12.9 12.8 0.13 13.1 12.9 0.10 0.28 <0.10 NS NS  Litter weight day 3, kg 24.0 24.8 25.1 24.5 24.0 23.7 0.53 22.5 25.0 0.45 0.20 <0.001 NS *  ADG of litter (day 3 to 26), kg/d 3.03b 3.16ab 3.14ab 3.32a 3.23ab 3.20ab 0.05 2.93 3.27 0.04 <0.01 <0.001 ** **  Milk yield, kg/d5 12.6b 12.7ab 12.8ab 13.2a 12.9ab 12.9ab 0.20 12.6 13.0 0.13 0.04 0.00 † † Subsequent reproduction  Weaning-to-estrus interval, d 5.3 5.4 6.1 6.0 5.0 5.0 0.76 8.3 4.4 0.62 0.79 <0.001 NS NS  Farrowing rate, %6 88.4 [78; 94] 95.6 [87; 99] 86.5 [75; 93] 97.2 [89; 99] 86.3 [75; 93] 89.6 [79; 95] 85.0 [76; 91] 93.6 [90; 96] 0.17 <0.01 NS NS  Total born piglets 19.7 20.2 19.1 19.9 19.8 20.4 0.49 18.3 20.4 0.40 0.48 <0.001 NS NS Dietary treatment, SID Lys g/kg2 6.19 6.90 7.63 8.33 9.04 9.76 Parity P-value3,4 Item 1 2 3 4 5 6 SEM Primi Multi SEM Trt Parity Lin Quad n 65 64 66 66 63 66 106 284 Sows  Parity 2.6 2.7 2.6 2.6 2.7 2.7 0.19 1.00 NS NS  Days in milk, d 26 26 26 26 25 26 0.14 26.4 25.3 0.11 0.83 <0.001 NS NS  ADFI, kg 6.36 6.44 6.46 6.48 6.48 6.47 0.05 5.88 6.66 0.04 0.32 <0.001 * NS  SID protein intake, g/d 824b 838ab 845ab 853a 857a 861a 6.20 772 874 5.13 <0.001 <0.001 *** NS  SID Lys intake, g/d 39.4f 44.2e 48.8d 53.5c 58.1b 63.9a 0.46 46.9 53.0 0.39 <0.001 <0.001 *** NS  Sow BW day 3, kg 249 250 245 251 247 248 3.39 206 264 2.90 0.79 <0.001 NS NS  BW loss (day 3 to 26), kg/d 0.54a 0.38ab 0.38ab 0.32ab 0.15b 0.16b 0.06 0.37 0.31 0.05 <0.001 0.20 *** NS  Sow BF day 3, mm 16.2ab 16.1ab 15.6b 17.0a 16.0ab 15.1b 0.38 15.2 16.3 0.31 <0.01 <0.01 NS †  BF loss (day 3 to 26), mm/d 0.16 0.15 0.16 0.17 0.16 0.15 0.01 0.17 0.15 0.01 0.29 <0.01 NS † Piglets  Litter size day 3 14.0 14.0 14.0 14.0 14.0 14.0 – 14.0 14.0 – – – – –  Litter size day 26 13.1 12.8 13.0 13.1 12.9 12.8 0.13 13.1 12.9 0.10 0.28 <0.10 NS NS  Litter weight day 3, kg 24.0 24.8 25.1 24.5 24.0 23.7 0.53 22.5 25.0 0.45 0.20 <0.001 NS *  ADG of litter (day 3 to 26), kg/d 3.03b 3.16ab 3.14ab 3.32a 3.23ab 3.20ab 0.05 2.93 3.27 0.04 <0.01 <0.001 ** **  Milk yield, kg/d5 12.6b 12.7ab 12.8ab 13.2a 12.9ab 12.9ab 0.20 12.6 13.0 0.13 0.04 0.00 † † Subsequent reproduction  Weaning-to-estrus interval, d 5.3 5.4 6.1 6.0 5.0 5.0 0.76 8.3 4.4 0.62 0.79 <0.001 NS NS  Farrowing rate, %6 88.4 [78; 94] 95.6 [87; 99] 86.5 [75; 93] 97.2 [89; 99] 86.3 [75; 93] 89.6 [79; 95] 85.0 [76; 91] 93.6 [90; 96] 0.17 <0.01 NS NS  Total born piglets 19.7 20.2 19.1 19.9 19.8 20.4 0.49 18.3 20.4 0.40 0.48 <0.001 NS NS 1For litter ADG, litter weight at day 3 was used as a covariate in the model. For sow BF change, sow BF thickness at day 3 was used as covariate in the model. 2Treatment 1 through 6: the calculated average SID Lys content for the dietary treatment fed to sows in the given treatment group of the 390-sow data set. 3P-values for the dietary treatment (Trt) and parity are from the ANOVA test using the MIXED procedure of SAS. The interaction, Trt × parity was not significant (P > 0.05). The greatest SEM values within diets or within parity are reported. 4Orthogonal polynomial contrasts were used to evaluate linear (lin) and quadratic (quad) effects of SID Lys: NS = not significant, † < 0.10, * < 0.05, ** < 0.01, *** < 0.001. 5Milk yield was estimated using equations from Hansen et al. (2012). 6Farrowing rate is considered a binomial response and was analyzed using a logistic regression. Results are given as means and the 95% confidence intervals are given in brackets. a–fWithin a row, values without common superscript letters differ (P < 0.05). Open in new tab Table 4. Effect of increasing standardized ileal digestible (SID) Lys on sow and litter performance, and subsequent reproduction (n = 390)1 Dietary treatment, SID Lys g/kg2 6.19 6.90 7.63 8.33 9.04 9.76 Parity P-value3,4 Item 1 2 3 4 5 6 SEM Primi Multi SEM Trt Parity Lin Quad n 65 64 66 66 63 66 106 284 Sows  Parity 2.6 2.7 2.6 2.6 2.7 2.7 0.19 1.00 NS NS  Days in milk, d 26 26 26 26 25 26 0.14 26.4 25.3 0.11 0.83 <0.001 NS NS  ADFI, kg 6.36 6.44 6.46 6.48 6.48 6.47 0.05 5.88 6.66 0.04 0.32 <0.001 * NS  SID protein intake, g/d 824b 838ab 845ab 853a 857a 861a 6.20 772 874 5.13 <0.001 <0.001 *** NS  SID Lys intake, g/d 39.4f 44.2e 48.8d 53.5c 58.1b 63.9a 0.46 46.9 53.0 0.39 <0.001 <0.001 *** NS  Sow BW day 3, kg 249 250 245 251 247 248 3.39 206 264 2.90 0.79 <0.001 NS NS  BW loss (day 3 to 26), kg/d 0.54a 0.38ab 0.38ab 0.32ab 0.15b 0.16b 0.06 0.37 0.31 0.05 <0.001 0.20 *** NS  Sow BF day 3, mm 16.2ab 16.1ab 15.6b 17.0a 16.0ab 15.1b 0.38 15.2 16.3 0.31 <0.01 <0.01 NS †  BF loss (day 3 to 26), mm/d 0.16 0.15 0.16 0.17 0.16 0.15 0.01 0.17 0.15 0.01 0.29 <0.01 NS † Piglets  Litter size day 3 14.0 14.0 14.0 14.0 14.0 14.0 – 14.0 14.0 – – – – –  Litter size day 26 13.1 12.8 13.0 13.1 12.9 12.8 0.13 13.1 12.9 0.10 0.28 <0.10 NS NS  Litter weight day 3, kg 24.0 24.8 25.1 24.5 24.0 23.7 0.53 22.5 25.0 0.45 0.20 <0.001 NS *  ADG of litter (day 3 to 26), kg/d 3.03b 3.16ab 3.14ab 3.32a 3.23ab 3.20ab 0.05 2.93 3.27 0.04 <0.01 <0.001 ** **  Milk yield, kg/d5 12.6b 12.7ab 12.8ab 13.2a 12.9ab 12.9ab 0.20 12.6 13.0 0.13 0.04 0.00 † † Subsequent reproduction  Weaning-to-estrus interval, d 5.3 5.4 6.1 6.0 5.0 5.0 0.76 8.3 4.4 0.62 0.79 <0.001 NS NS  Farrowing rate, %6 88.4 [78; 94] 95.6 [87; 99] 86.5 [75; 93] 97.2 [89; 99] 86.3 [75; 93] 89.6 [79; 95] 85.0 [76; 91] 93.6 [90; 96] 0.17 <0.01 NS NS  Total born piglets 19.7 20.2 19.1 19.9 19.8 20.4 0.49 18.3 20.4 0.40 0.48 <0.001 NS NS Dietary treatment, SID Lys g/kg2 6.19 6.90 7.63 8.33 9.04 9.76 Parity P-value3,4 Item 1 2 3 4 5 6 SEM Primi Multi SEM Trt Parity Lin Quad n 65 64 66 66 63 66 106 284 Sows  Parity 2.6 2.7 2.6 2.6 2.7 2.7 0.19 1.00 NS NS  Days in milk, d 26 26 26 26 25 26 0.14 26.4 25.3 0.11 0.83 <0.001 NS NS  ADFI, kg 6.36 6.44 6.46 6.48 6.48 6.47 0.05 5.88 6.66 0.04 0.32 <0.001 * NS  SID protein intake, g/d 824b 838ab 845ab 853a 857a 861a 6.20 772 874 5.13 <0.001 <0.001 *** NS  SID Lys intake, g/d 39.4f 44.2e 48.8d 53.5c 58.1b 63.9a 0.46 46.9 53.0 0.39 <0.001 <0.001 *** NS  Sow BW day 3, kg 249 250 245 251 247 248 3.39 206 264 2.90 0.79 <0.001 NS NS  BW loss (day 3 to 26), kg/d 0.54a 0.38ab 0.38ab 0.32ab 0.15b 0.16b 0.06 0.37 0.31 0.05 <0.001 0.20 *** NS  Sow BF day 3, mm 16.2ab 16.1ab 15.6b 17.0a 16.0ab 15.1b 0.38 15.2 16.3 0.31 <0.01 <0.01 NS †  BF loss (day 3 to 26), mm/d 0.16 0.15 0.16 0.17 0.16 0.15 0.01 0.17 0.15 0.01 0.29 <0.01 NS † Piglets  Litter size day 3 14.0 14.0 14.0 14.0 14.0 14.0 – 14.0 14.0 – – – – –  Litter size day 26 13.1 12.8 13.0 13.1 12.9 12.8 0.13 13.1 12.9 0.10 0.28 <0.10 NS NS  Litter weight day 3, kg 24.0 24.8 25.1 24.5 24.0 23.7 0.53 22.5 25.0 0.45 0.20 <0.001 NS *  ADG of litter (day 3 to 26), kg/d 3.03b 3.16ab 3.14ab 3.32a 3.23ab 3.20ab 0.05 2.93 3.27 0.04 <0.01 <0.001 ** **  Milk yield, kg/d5 12.6b 12.7ab 12.8ab 13.2a 12.9ab 12.9ab 0.20 12.6 13.0 0.13 0.04 0.00 † † Subsequent reproduction  Weaning-to-estrus interval, d 5.3 5.4 6.1 6.0 5.0 5.0 0.76 8.3 4.4 0.62 0.79 <0.001 NS NS  Farrowing rate, %6 88.4 [78; 94] 95.6 [87; 99] 86.5 [75; 93] 97.2 [89; 99] 86.3 [75; 93] 89.6 [79; 95] 85.0 [76; 91] 93.6 [90; 96] 0.17 <0.01 NS NS  Total born piglets 19.7 20.2 19.1 19.9 19.8 20.4 0.49 18.3 20.4 0.40 0.48 <0.001 NS NS 1For litter ADG, litter weight at day 3 was used as a covariate in the model. For sow BF change, sow BF thickness at day 3 was used as covariate in the model. 2Treatment 1 through 6: the calculated average SID Lys content for the dietary treatment fed to sows in the given treatment group of the 390-sow data set. 3P-values for the dietary treatment (Trt) and parity are from the ANOVA test using the MIXED procedure of SAS. The interaction, Trt × parity was not significant (P > 0.05). The greatest SEM values within diets or within parity are reported. 4Orthogonal polynomial contrasts were used to evaluate linear (lin) and quadratic (quad) effects of SID Lys: NS = not significant, † < 0.10, * < 0.05, ** < 0.01, *** < 0.001. 5Milk yield was estimated using equations from Hansen et al. (2012). 6Farrowing rate is considered a binomial response and was analyzed using a logistic regression. Results are given as means and the 95% confidence intervals are given in brackets. a–fWithin a row, values without common superscript letters differ (P < 0.05). Open in new tab Figure 1. Open in new tabDownload slide The effect of increasing standardized ileal digestible (SID) Lys on litter ADG based on the 390-sow data set. Data were best described by a linear broken-line model. The breakpoint is presented together with SEM and the P-value for the slope below the breakpoint is presented. Litter ADG increased until a breakpoint at 8.11 ± 0.66 g/kg of SID Lys and reached a plateau at 2.93 kg/d and 3.36 kg for primi- and multiparous sows, respectively (P < 0.05). For Xi < 8.11, ADG = 2.93primi or 3.36multi − 0.10 × (8.11 − Xi). The value, Xi, is the concentration of SID Lys, g/kg, for the individual sow, i. The symbols, black diamonds (♦), are the least squared means from the ANOVA test for dietary treatment 1 through 6. The vertical lines (|) are the 95% CI for the least squared means within each treatment. The fitted models from the NLmixed procedure are plotted as the given lines. Figure 1. Open in new tabDownload slide The effect of increasing standardized ileal digestible (SID) Lys on litter ADG based on the 390-sow data set. Data were best described by a linear broken-line model. The breakpoint is presented together with SEM and the P-value for the slope below the breakpoint is presented. Litter ADG increased until a breakpoint at 8.11 ± 0.66 g/kg of SID Lys and reached a plateau at 2.93 kg/d and 3.36 kg for primi- and multiparous sows, respectively (P < 0.05). For Xi < 8.11, ADG = 2.93primi or 3.36multi − 0.10 × (8.11 − Xi). The value, Xi, is the concentration of SID Lys, g/kg, for the individual sow, i. The symbols, black diamonds (♦), are the least squared means from the ANOVA test for dietary treatment 1 through 6. The vertical lines (|) are the 95% CI for the least squared means within each treatment. The fitted models from the NLmixed procedure are plotted as the given lines. Figure 2. Open in new tabDownload slide Litter ADG, for the 71-sow data set, at 3 to 10, 10 to 17, and 17 to 24 days in milk (P < 0.001). Error bars indicate the SEM. Figure 2. Open in new tabDownload slide Litter ADG, for the 71-sow data set, at 3 to 10, 10 to 17, and 17 to 24 days in milk (P < 0.001). Error bars indicate the SEM. The ADFI was 5.88 and 6.66 kg/d for primi- and multiparous sows (P < 0.001; Table 4), respectively, but was not different between dietary treatments (P = 0.32). The daily SID Lys intake increased linearly by 67% from 35 to 59 g/d and 61% from 41 to 66 g/d for primi- and multiparous sows, respectively (P = 0.001; data not shown). Concomitantly, the daily SID CP intake increased slightly from 737 to 794 g/d and from 856 to 886 g/d for primi- and multiparous sows, respectively (P = 0.001; data not shown), corresponding to 7.8% and 3.4% increment. Subsequent WEI (P = 0.79; Table 4), farrowing rate (P = 0.17), and total born piglets in the next litter (P = 0.48) were not affected by dietary Lys supply. Results on sow body mobilization showed that a tendency toward a quadratic effect was observed for BF loss during lactation, with a peak BF loss around 8.23 g/kg of SID Lys (P < 0.10; Table 4). Based on a linear broken-line regression model, sows required 9.05 ± 0.01 g/kg of SID Lys to minimize lactation BW loss to 0.17 kg/d (P < 0.001; Fig. 3A). The BW loss increased to 0.54 kg/d when sows were fed the lowest dietary Lys level (6.19 g/kg of SID Lys). The daily mobilization rates were equivalent to a total lactation BW loss of 4 kg in the breakpoint (9.05 g/kg of SID Lys) and 12 kg at the lowest dietary Lys level (6.19 g/kg of SID Lys). There was no difference in the BW loss between primi- and multiparous sows, respectively (P = 0.20). Based on a linear broken-line regression model, body protein loss was minimized at 9.22 ± 0.96 g/kg of SID Lys (P < 0.05; Fig. 3B), whereas no clear linear or quadratic effect was observed for body fat mobilization (Table 5). Table 5. The effect of increasing standardized ileal digestible (SID) Lys on sow body composition and body mobilization (n = 71)1 Dietary treatment, SID Lys g/kg2 6.27 6.91 7.58 8.23 8.86 9.53 P-value3,4 Item 1 2 3 4 5 6 SEM Trt Lin Quad n 12 12 11 12 12 12 Body fat day 3, kg 71.4 64.8 69.5 64.6 63.8 66.2 3.45 0.33 NS NS Body protein day 3, kg 42.3 43.0 41.6 40.6 42.5 41.3 1.34 0.43 NS NS Body fat loss (day 3 to 26), kg 10.0ab 2.9bc 10.7a 12.0a 2.0c 4.1bc 2.54 <0.01 NS NS Body protein loss (day 3 to 26), kg5 1.78a 0.71ab 1.57a 0.61ab −0.11b −0.13b 0.64 <0.05 ** NS Dietary treatment, SID Lys g/kg2 6.27 6.91 7.58 8.23 8.86 9.53 P-value3,4 Item 1 2 3 4 5 6 SEM Trt Lin Quad n 12 12 11 12 12 12 Body fat day 3, kg 71.4 64.8 69.5 64.6 63.8 66.2 3.45 0.33 NS NS Body protein day 3, kg 42.3 43.0 41.6 40.6 42.5 41.3 1.34 0.43 NS NS Body fat loss (day 3 to 26), kg 10.0ab 2.9bc 10.7a 12.0a 2.0c 4.1bc 2.54 <0.01 NS NS Body protein loss (day 3 to 26), kg5 1.78a 0.71ab 1.57a 0.61ab −0.11b −0.13b 0.64 <0.05 ** NS 1For changes in pools of body fat and protein, sow BW and back fat thickness was used as a covariate in the model, respectively. 2Treatment 1 through 6: the calculated average SID Lys content for the dietary treatment fed to sows in the given treatment group of the 71-sow data set. 3P-values for the dietary treatment (Trt) are from the ANOVA test using the MIXED procedure of SAS. The greatest SEM values within diets are reported. 4Orthogonal polynomial contrasts were used to evaluate linear (lin) and quadratic (quad) effects of SID Lys: NS = not significant, ** < 0.01. 5Negative values indicate a gain. a–cWithin a row, values without common superscript letters differ (P < 0.05). Open in new tab Table 5. The effect of increasing standardized ileal digestible (SID) Lys on sow body composition and body mobilization (n = 71)1 Dietary treatment, SID Lys g/kg2 6.27 6.91 7.58 8.23 8.86 9.53 P-value3,4 Item 1 2 3 4 5 6 SEM Trt Lin Quad n 12 12 11 12 12 12 Body fat day 3, kg 71.4 64.8 69.5 64.6 63.8 66.2 3.45 0.33 NS NS Body protein day 3, kg 42.3 43.0 41.6 40.6 42.5 41.3 1.34 0.43 NS NS Body fat loss (day 3 to 26), kg 10.0ab 2.9bc 10.7a 12.0a 2.0c 4.1bc 2.54 <0.01 NS NS Body protein loss (day 3 to 26), kg5 1.78a 0.71ab 1.57a 0.61ab −0.11b −0.13b 0.64 <0.05 ** NS Dietary treatment, SID Lys g/kg2 6.27 6.91 7.58 8.23 8.86 9.53 P-value3,4 Item 1 2 3 4 5 6 SEM Trt Lin Quad n 12 12 11 12 12 12 Body fat day 3, kg 71.4 64.8 69.5 64.6 63.8 66.2 3.45 0.33 NS NS Body protein day 3, kg 42.3 43.0 41.6 40.6 42.5 41.3 1.34 0.43 NS NS Body fat loss (day 3 to 26), kg 10.0ab 2.9bc 10.7a 12.0a 2.0c 4.1bc 2.54 <0.01 NS NS Body protein loss (day 3 to 26), kg5 1.78a 0.71ab 1.57a 0.61ab −0.11b −0.13b 0.64 <0.05 ** NS 1For changes in pools of body fat and protein, sow BW and back fat thickness was used as a covariate in the model, respectively. 2Treatment 1 through 6: the calculated average SID Lys content for the dietary treatment fed to sows in the given treatment group of the 71-sow data set. 3P-values for the dietary treatment (Trt) are from the ANOVA test using the MIXED procedure of SAS. The greatest SEM values within diets are reported. 4Orthogonal polynomial contrasts were used to evaluate linear (lin) and quadratic (quad) effects of SID Lys: NS = not significant, ** < 0.01. 5Negative values indicate a gain. a–cWithin a row, values without common superscript letters differ (P < 0.05). Open in new tab Figure 3. Open in new tabDownload slide The effect of increasing standardized ileal digestible (SID) Lys on (A) sow BW loss based on the 390-sow data set and (B) sow body protein loss based on the 71-sow data set. Data were best described by linear broken-line models. The breakpoints are presented together with SEM and the P-values for the slopes below the breakpoints are presented. (A) Sow BW loss decreased until a breakpoint at 9.05 ± 0.01 g/kg of SID Lys and reached a plateau at 0.17 kg/d (P < 0.001). For Xi < 9.05, sow BW loss, kg/d = 0.17 + 0.12 × (9.05 − Xi). (B) Sow body protein loss decreased until a breakpoint at 9.22 ± 0.96 g/kg of SID Lys and reached a plateau at 0.23 kg (P < 0.05). For Xi < 9.22, sow body protein loss, kg = 0.23 + 0.7 × (9.22 − Xi). Negative values indicate a gain. The value, Xi, is the concentration of SID Lys, g/kg, for the individual sow, i. The symbols, black diamonds (♦), are the least squared means from the ANOVA test for dietary treatment 1 through 6. The vertical lines (|) are the 95% CI for the least squared means within each treatment. The fitted models from the NLmixed procedure are plotted as the given lines. Figure 3. Open in new tabDownload slide The effect of increasing standardized ileal digestible (SID) Lys on (A) sow BW loss based on the 390-sow data set and (B) sow body protein loss based on the 71-sow data set. Data were best described by linear broken-line models. The breakpoints are presented together with SEM and the P-values for the slopes below the breakpoints are presented. (A) Sow BW loss decreased until a breakpoint at 9.05 ± 0.01 g/kg of SID Lys and reached a plateau at 0.17 kg/d (P < 0.001). For Xi < 9.05, sow BW loss, kg/d = 0.17 + 0.12 × (9.05 − Xi). (B) Sow body protein loss decreased until a breakpoint at 9.22 ± 0.96 g/kg of SID Lys and reached a plateau at 0.23 kg (P < 0.05). For Xi < 9.22, sow body protein loss, kg = 0.23 + 0.7 × (9.22 − Xi). Negative values indicate a gain. The value, Xi, is the concentration of SID Lys, g/kg, for the individual sow, i. The symbols, black diamonds (♦), are the least squared means from the ANOVA test for dietary treatment 1 through 6. The vertical lines (|) are the 95% CI for the least squared means within each treatment. The fitted models from the NLmixed procedure are plotted as the given lines. Sow Plasma Metabolites No evidence of dietary effects were found on plasma concentrations of creatinine (P = 0.20; Table 6), glucose (P = 0.40), TAG (P = 0.96), and lactate (P = 0.90). However, fitting a 2-slope linear broken-line, NEFA increased (P = 0.13) until 7.50 ± 0.42 g/kg of SID Lys and decreased (P = 0.11) at greater SID Lys levels (Fig. 4A). The greatest plasma concentration of NEFA appeared in early lactation and decreased until peak lactation. Based on linear broken-line analyses, PUN decreased until a breakpoint of 7.02 ± 0.30 (P = 0.10) at 3 DIM, 8.10 ± 0.38 (P = 0.01) at 10 DIM, 8.73 ± 0.33 (P < 0.01) at 17 DIM, and 8.32 ± 0.26 (P < 0.01) g/kg of SID Lys at 24 DIM (Fig. 4B). Table 6. Effect of increasing standardized ileal digestible (SID) Lys on plasma creatinine, urea, glucose, triacylglycerol (TAG), lactate, and NEFA at 3, 10, 17, and 24 days in milk (DIM) (n = 71) Dietary treatment, SID Lys g/kg1 6.27 6.91 7.58 8.23 8.86 9.53 DIM P-value2,3 Item 1 2 3 4 5 6 SEM 3 10 17 24 SEM Trt DIM Trt × DIM Lin Quad n 48 48 44 48 48 48 71 71 71 71 Creatinine, µmol/L 158 156 164 146 157 155 5.0 157ab 159a 154ab 153b 2.85 0.20 <0.10 0.90 NS NS Urea, mmol/L 4.42a 3.73b 3.62bc 3.02d 3.19bcd 3.12cd 0.14 2.57c 3.51b 4.00a 3.99a 0.08 <0.001 <0.001 <0.001 *** ** Glucose, mmol/L 5.39 5.50 5.39 5.29 5.59 5.40 0.1 5.50a 5.47a 5.63a 5.10b 0.06 0.40 <0.001 0.43 NS NS TAG, mmol/L 0.31 0.30 0.32 0.30 0.31 0.32 0.02 0.33a 0.31a 0.33a 0.26b 0.01 0.96 <0.001 0.47 NS NS Lactate4, mmol/L 1.3 [1.1; 1.6] 1.3 [1.1; 1.5] 1.4 [1.2; 1.6] 1.4 [1.2; 1.7] 1.4 [1.2; 1.6] 1.3 [1.1; 1.6] – 1.6a [1.4; 1.8] 1.3b [1.2; 1.5] 1.3b [1.1; 1.5] 1.2b [1.1; 1.4] 0.90 <0.001 0.36 NS NS NEFA4, µmol/L 113 [70; 160] 126 [55; 132] 190 [81; 184] 168 [99; 226] 128 [71; 164] 123 [62; 144] – 300a [174; 353] 170b [116; 229] 90c [55; 110] 81c [32; 64] 0.46 <0.001 0.95 NS † Dietary treatment, SID Lys g/kg1 6.27 6.91 7.58 8.23 8.86 9.53 DIM P-value2,3 Item 1 2 3 4 5 6 SEM 3 10 17 24 SEM Trt DIM Trt × DIM Lin Quad n 48 48 44 48 48 48 71 71 71 71 Creatinine, µmol/L 158 156 164 146 157 155 5.0 157ab 159a 154ab 153b 2.85 0.20 <0.10 0.90 NS NS Urea, mmol/L 4.42a 3.73b 3.62bc 3.02d 3.19bcd 3.12cd 0.14 2.57c 3.51b 4.00a 3.99a 0.08 <0.001 <0.001 <0.001 *** ** Glucose, mmol/L 5.39 5.50 5.39 5.29 5.59 5.40 0.1 5.50a 5.47a 5.63a 5.10b 0.06 0.40 <0.001 0.43 NS NS TAG, mmol/L 0.31 0.30 0.32 0.30 0.31 0.32 0.02 0.33a 0.31a 0.33a 0.26b 0.01 0.96 <0.001 0.47 NS NS Lactate4, mmol/L 1.3 [1.1; 1.6] 1.3 [1.1; 1.5] 1.4 [1.2; 1.6] 1.4 [1.2; 1.7] 1.4 [1.2; 1.6] 1.3 [1.1; 1.6] – 1.6a [1.4; 1.8] 1.3b [1.2; 1.5] 1.3b [1.1; 1.5] 1.2b [1.1; 1.4] 0.90 <0.001 0.36 NS NS NEFA4, µmol/L 113 [70; 160] 126 [55; 132] 190 [81; 184] 168 [99; 226] 128 [71; 164] 123 [62; 144] – 300a [174; 353] 170b [116; 229] 90c [55; 110] 81c [32; 64] 0.46 <0.001 0.95 NS † 1Treatment 1 through 6: the calculated average SID Lys content for the dietary treatment fed to sows in the given treatment group of the 71-sow data set. 2P-values for the dietary treatment (Trt) and DIM are from the ANOVA test using the MIXED procedure of SAS. The greatest SEM values within diets or within DIM are reported. 3Orthogonal polynomial contrasts were used to evaluate linear (lin) and quadratic (quad) effects of SID Lys: NS = not significant, † < 0.10, ** < 0.01, *** < 0.001. 4Data on plasma NEFA and lactate were log-transformed to make data conform to variance homogeneity. Results are given as back-transformed estimates and the 95% confidence intervals are given in brackets. a–dWithin a row, values without common superscript letters differ (P < 0.05). Open in new tab Table 6. Effect of increasing standardized ileal digestible (SID) Lys on plasma creatinine, urea, glucose, triacylglycerol (TAG), lactate, and NEFA at 3, 10, 17, and 24 days in milk (DIM) (n = 71) Dietary treatment, SID Lys g/kg1 6.27 6.91 7.58 8.23 8.86 9.53 DIM P-value2,3 Item 1 2 3 4 5 6 SEM 3 10 17 24 SEM Trt DIM Trt × DIM Lin Quad n 48 48 44 48 48 48 71 71 71 71 Creatinine, µmol/L 158 156 164 146 157 155 5.0 157ab 159a 154ab 153b 2.85 0.20 <0.10 0.90 NS NS Urea, mmol/L 4.42a 3.73b 3.62bc 3.02d 3.19bcd 3.12cd 0.14 2.57c 3.51b 4.00a 3.99a 0.08 <0.001 <0.001 <0.001 *** ** Glucose, mmol/L 5.39 5.50 5.39 5.29 5.59 5.40 0.1 5.50a 5.47a 5.63a 5.10b 0.06 0.40 <0.001 0.43 NS NS TAG, mmol/L 0.31 0.30 0.32 0.30 0.31 0.32 0.02 0.33a 0.31a 0.33a 0.26b 0.01 0.96 <0.001 0.47 NS NS Lactate4, mmol/L 1.3 [1.1; 1.6] 1.3 [1.1; 1.5] 1.4 [1.2; 1.6] 1.4 [1.2; 1.7] 1.4 [1.2; 1.6] 1.3 [1.1; 1.6] – 1.6a [1.4; 1.8] 1.3b [1.2; 1.5] 1.3b [1.1; 1.5] 1.2b [1.1; 1.4] 0.90 <0.001 0.36 NS NS NEFA4, µmol/L 113 [70; 160] 126 [55; 132] 190 [81; 184] 168 [99; 226] 128 [71; 164] 123 [62; 144] – 300a [174; 353] 170b [116; 229] 90c [55; 110] 81c [32; 64] 0.46 <0.001 0.95 NS † Dietary treatment, SID Lys g/kg1 6.27 6.91 7.58 8.23 8.86 9.53 DIM P-value2,3 Item 1 2 3 4 5 6 SEM 3 10 17 24 SEM Trt DIM Trt × DIM Lin Quad n 48 48 44 48 48 48 71 71 71 71 Creatinine, µmol/L 158 156 164 146 157 155 5.0 157ab 159a 154ab 153b 2.85 0.20 <0.10 0.90 NS NS Urea, mmol/L 4.42a 3.73b 3.62bc 3.02d 3.19bcd 3.12cd 0.14 2.57c 3.51b 4.00a 3.99a 0.08 <0.001 <0.001 <0.001 *** ** Glucose, mmol/L 5.39 5.50 5.39 5.29 5.59 5.40 0.1 5.50a 5.47a 5.63a 5.10b 0.06 0.40 <0.001 0.43 NS NS TAG, mmol/L 0.31 0.30 0.32 0.30 0.31 0.32 0.02 0.33a 0.31a 0.33a 0.26b 0.01 0.96 <0.001 0.47 NS NS Lactate4, mmol/L 1.3 [1.1; 1.6] 1.3 [1.1; 1.5] 1.4 [1.2; 1.6] 1.4 [1.2; 1.7] 1.4 [1.2; 1.6] 1.3 [1.1; 1.6] – 1.6a [1.4; 1.8] 1.3b [1.2; 1.5] 1.3b [1.1; 1.5] 1.2b [1.1; 1.4] 0.90 <0.001 0.36 NS NS NEFA4, µmol/L 113 [70; 160] 126 [55; 132] 190 [81; 184] 168 [99; 226] 128 [71; 164] 123 [62; 144] – 300a [174; 353] 170b [116; 229] 90c [55; 110] 81c [32; 64] 0.46 <0.001 0.95 NS † 1Treatment 1 through 6: the calculated average SID Lys content for the dietary treatment fed to sows in the given treatment group of the 71-sow data set. 2P-values for the dietary treatment (Trt) and DIM are from the ANOVA test using the MIXED procedure of SAS. The greatest SEM values within diets or within DIM are reported. 3Orthogonal polynomial contrasts were used to evaluate linear (lin) and quadratic (quad) effects of SID Lys: NS = not significant, † < 0.10, ** < 0.01, *** < 0.001. 4Data on plasma NEFA and lactate were log-transformed to make data conform to variance homogeneity. Results are given as back-transformed estimates and the 95% confidence intervals are given in brackets. a–dWithin a row, values without common superscript letters differ (P < 0.05). Open in new tab Figure 4. Open in new tabDownload slide The effect of increasing standardized ileal digestible (SID) Lys on (A) plasma NEFA (based on log-transformed data) and (B) plasma urea nitrogen. The breakpoints are presented together with SEM and the P-values for the slopes above or below the breakpoints are presented. (A) The log-transformed data for plasma NEFA were best described by 2-slope linear broken-line models: Yi = 5.97DIM3 or 5.46DIM10 or 4.77DIM17 or 4.57DIM24 − 0.43 × (7.50 − Xi) for Xi < 7.50 and Yi = 5.97DIM3 or 5.46DIM10 or 4.77DIM17 or 4.57DIM24 − 0.22 × (Xi − 7.50) for Xi > 7.50. Plasma NEFA increased (P = 0.13) until a breakpoint of 7.50 ± 0.42 g/kg of SID Lys reaching 392, 236, 118, and 96 µmol/L (back-transformed estimates) at 3, 10, 17, and 24 days in milk (DIM), respectively, and thereafter, it decreased at greater SID Lys levels (P = 0.11). (B) Plasma urea nitrogen was best described by 1-slope linear broken-line models: Yi DIM3 = 2.34 + 0.79 × (7.02 − Xi) for Xi < 7.02, Yi DIM10 = 3.06 + 0.63 × (8.10 − Xi) for Xi < 8.10, Yi DIM17 = 3.43 + 0.62 × (8.73 − Xi) for Xi < 8.73, Yi DIM24 = 3.44 + 0.79 × (8.32 − Xi) for Xi < 8.32. At 3, 10, 17, and 24 DIM, PUN decreased until breakpoints of 7.02 ± 0.30 g/kg of SID Lys at 2.34 mmol/L (P = 0.10), 8.10 ± 0.38 g/kg of SID Lys at 3.06 mmol/L (P = 0.01), 8.73 ± 0.33 g/kg of SID Lys at 3.43 mmol/L (P < 0.01), and 8.32 ± 0.26 g/kg of SID Lys at 3.44 mmol/L (P < 0.01), respectively. The value, Xi, is the concentration of SID Lys, g/kg, for the individual sow, i. The least squared means from the ANOVA test are plotted as the given symbols, whereas the fitted models from the NLmixed procedure are plotted as the given lines. Figure 4. Open in new tabDownload slide The effect of increasing standardized ileal digestible (SID) Lys on (A) plasma NEFA (based on log-transformed data) and (B) plasma urea nitrogen. The breakpoints are presented together with SEM and the P-values for the slopes above or below the breakpoints are presented. (A) The log-transformed data for plasma NEFA were best described by 2-slope linear broken-line models: Yi = 5.97DIM3 or 5.46DIM10 or 4.77DIM17 or 4.57DIM24 − 0.43 × (7.50 − Xi) for Xi < 7.50 and Yi = 5.97DIM3 or 5.46DIM10 or 4.77DIM17 or 4.57DIM24 − 0.22 × (Xi − 7.50) for Xi > 7.50. Plasma NEFA increased (P = 0.13) until a breakpoint of 7.50 ± 0.42 g/kg of SID Lys reaching 392, 236, 118, and 96 µmol/L (back-transformed estimates) at 3, 10, 17, and 24 days in milk (DIM), respectively, and thereafter, it decreased at greater SID Lys levels (P = 0.11). (B) Plasma urea nitrogen was best described by 1-slope linear broken-line models: Yi DIM3 = 2.34 + 0.79 × (7.02 − Xi) for Xi < 7.02, Yi DIM10 = 3.06 + 0.63 × (8.10 − Xi) for Xi < 8.10, Yi DIM17 = 3.43 + 0.62 × (8.73 − Xi) for Xi < 8.73, Yi DIM24 = 3.44 + 0.79 × (8.32 − Xi) for Xi < 8.32. At 3, 10, 17, and 24 DIM, PUN decreased until breakpoints of 7.02 ± 0.30 g/kg of SID Lys at 2.34 mmol/L (P = 0.10), 8.10 ± 0.38 g/kg of SID Lys at 3.06 mmol/L (P = 0.01), 8.73 ± 0.33 g/kg of SID Lys at 3.43 mmol/L (P < 0.01), and 8.32 ± 0.26 g/kg of SID Lys at 3.44 mmol/L (P < 0.01), respectively. The value, Xi, is the concentration of SID Lys, g/kg, for the individual sow, i. The least squared means from the ANOVA test are plotted as the given symbols, whereas the fitted models from the NLmixed procedure are plotted as the given lines. Milk Components The milk composition is presented in Table 7 and Fig. 5. When fitting linear broken-line for milk fat it was maximized at and above 7.80 ± 0.36 g/kg of SID Lys (P < 0.05; Fig. 5A). Likewise, milk DM and energy were maximized at 7.81 ± 0.51 g/kg of SID Lys (P = 0.06; Fig. 5B) and 7.66 ± 0.29 g/kg of SID Lys (P = 0.06; Fig. 5C), respectively. Milk urea content was best described by 2-slope linear broken-line models. Milk urea decreased (P < 0.05) until 7.33 ± 0.22 g/kg of SID Lys where it was minimized and then increased slightly at greater SID Lys levels (Fig. 5D). Concentrations of milk protein (P = 0.93) and casein (P = 0.88) were not affected by the dietary Lys supply. Table 7. Effect of increasing standardized ileal digestible (SID) Lys on milk composition at 3, 10, 17, and 24 days in milk (DIM) (n = 71) Dietary treatment, SID Lys g/kg1 6.27 6.91 7.58 8.23 8.86 9.53 DIM P-value2,3 Item 1 2 3 4 5 6 SEM 3 10 17 24 SEM Trt DIM Trt × DIM Lin Quad n 48 48 44 48 48 48 71 71 71 71 DM, % 17.2b 17.6ab 17.8ab 17.8ab 18.2a 17.8ab 0.17 18.9a 17.5b 17.4b 17.2b 0.12 <0.001 <0.001 0.87 *** * Lactose, % 5.24 5.18 5.16 5.19 5.13 5.22 0.03 4.96c 5.20b 5.27a 5.33a 0.02 <0.10 <0.001 0.96 NS * Fat, % 6.33b 6.82ab 6.96ab 6.94ab 7.32a 7.06a 0.17 7.92a 6.76b 6.70b 6.24c 0.13 <0.01 <0.001 0.77 *** † Protein, % 4.95 4.91 4.99 4.96 5.01 4.94 0.08 5.45a 4.75c 4.70c 4.93b 0.06 0.93 <0.001 0.65 NS NS Casein, % 4.07 3.96 4.06 4.03 4.05 4.00 0.08 4.40a 3.86c 3.82c 4.04b 0.05 0.88 <0.001 0.68 NS NS Urea, mg/dL 44.16a 36.80b 33.28b 33.61b 32.17b 37.12b 1.85 31.90c 33.60bc 36.39b 42.88a 1.39 <0.001 <0.001 0.20 *** *** Energy, MJ/kg4 4.50b 4.67ab 4.73ab 4.73ab 4.88a 4.73ab 0.06 5.18a 4.61b 4.56b 4.47b 0.05 <0.01 <0.001 0.90 *** * Dietary treatment, SID Lys g/kg1 6.27 6.91 7.58 8.23 8.86 9.53 DIM P-value2,3 Item 1 2 3 4 5 6 SEM 3 10 17 24 SEM Trt DIM Trt × DIM Lin Quad n 48 48 44 48 48 48 71 71 71 71 DM, % 17.2b 17.6ab 17.8ab 17.8ab 18.2a 17.8ab 0.17 18.9a 17.5b 17.4b 17.2b 0.12 <0.001 <0.001 0.87 *** * Lactose, % 5.24 5.18 5.16 5.19 5.13 5.22 0.03 4.96c 5.20b 5.27a 5.33a 0.02 <0.10 <0.001 0.96 NS * Fat, % 6.33b 6.82ab 6.96ab 6.94ab 7.32a 7.06a 0.17 7.92a 6.76b 6.70b 6.24c 0.13 <0.01 <0.001 0.77 *** † Protein, % 4.95 4.91 4.99 4.96 5.01 4.94 0.08 5.45a 4.75c 4.70c 4.93b 0.06 0.93 <0.001 0.65 NS NS Casein, % 4.07 3.96 4.06 4.03 4.05 4.00 0.08 4.40a 3.86c 3.82c 4.04b 0.05 0.88 <0.001 0.68 NS NS Urea, mg/dL 44.16a 36.80b 33.28b 33.61b 32.17b 37.12b 1.85 31.90c 33.60bc 36.39b 42.88a 1.39 <0.001 <0.001 0.20 *** *** Energy, MJ/kg4 4.50b 4.67ab 4.73ab 4.73ab 4.88a 4.73ab 0.06 5.18a 4.61b 4.56b 4.47b 0.05 <0.01 <0.001 0.90 *** * 1Treatment 1 through 6: the calculated average SID Lys content for the dietary treatment fed to sows in the given treatment group of the 71-sow data set. 2P-values for the dietary treatment (Trt) and DIM are from the ANOVA test using the MIXED procedure of SAS. The greatest SEM values within diets or within DIM are reported. 3Orthogonal polynomial contrasts were used to evaluate linear (lin) and quadratic (quad) effects of SID Lys: NS = not significant, † < 0.10, * < 0.05, *** < 0.001. 4Gross energy of milk was estimated, using the equation: GE (MJ/kg) = (38.9, MJ/kg × milk fat, % + 23.8, MJ/kg × milk protein, % + 16.3, MJ/kg × lactose, %)/100%, given by Chwalibog (2006). a–cWithin a row, values without common superscript letters differ (P < 0.05). Open in new tab Table 7. Effect of increasing standardized ileal digestible (SID) Lys on milk composition at 3, 10, 17, and 24 days in milk (DIM) (n = 71) Dietary treatment, SID Lys g/kg1 6.27 6.91 7.58 8.23 8.86 9.53 DIM P-value2,3 Item 1 2 3 4 5 6 SEM 3 10 17 24 SEM Trt DIM Trt × DIM Lin Quad n 48 48 44 48 48 48 71 71 71 71 DM, % 17.2b 17.6ab 17.8ab 17.8ab 18.2a 17.8ab 0.17 18.9a 17.5b 17.4b 17.2b 0.12 <0.001 <0.001 0.87 *** * Lactose, % 5.24 5.18 5.16 5.19 5.13 5.22 0.03 4.96c 5.20b 5.27a 5.33a 0.02 <0.10 <0.001 0.96 NS * Fat, % 6.33b 6.82ab 6.96ab 6.94ab 7.32a 7.06a 0.17 7.92a 6.76b 6.70b 6.24c 0.13 <0.01 <0.001 0.77 *** † Protein, % 4.95 4.91 4.99 4.96 5.01 4.94 0.08 5.45a 4.75c 4.70c 4.93b 0.06 0.93 <0.001 0.65 NS NS Casein, % 4.07 3.96 4.06 4.03 4.05 4.00 0.08 4.40a 3.86c 3.82c 4.04b 0.05 0.88 <0.001 0.68 NS NS Urea, mg/dL 44.16a 36.80b 33.28b 33.61b 32.17b 37.12b 1.85 31.90c 33.60bc 36.39b 42.88a 1.39 <0.001 <0.001 0.20 *** *** Energy, MJ/kg4 4.50b 4.67ab 4.73ab 4.73ab 4.88a 4.73ab 0.06 5.18a 4.61b 4.56b 4.47b 0.05 <0.01 <0.001 0.90 *** * Dietary treatment, SID Lys g/kg1 6.27 6.91 7.58 8.23 8.86 9.53 DIM P-value2,3 Item 1 2 3 4 5 6 SEM 3 10 17 24 SEM Trt DIM Trt × DIM Lin Quad n 48 48 44 48 48 48 71 71 71 71 DM, % 17.2b 17.6ab 17.8ab 17.8ab 18.2a 17.8ab 0.17 18.9a 17.5b 17.4b 17.2b 0.12 <0.001 <0.001 0.87 *** * Lactose, % 5.24 5.18 5.16 5.19 5.13 5.22 0.03 4.96c 5.20b 5.27a 5.33a 0.02 <0.10 <0.001 0.96 NS * Fat, % 6.33b 6.82ab 6.96ab 6.94ab 7.32a 7.06a 0.17 7.92a 6.76b 6.70b 6.24c 0.13 <0.01 <0.001 0.77 *** † Protein, % 4.95 4.91 4.99 4.96 5.01 4.94 0.08 5.45a 4.75c 4.70c 4.93b 0.06 0.93 <0.001 0.65 NS NS Casein, % 4.07 3.96 4.06 4.03 4.05 4.00 0.08 4.40a 3.86c 3.82c 4.04b 0.05 0.88 <0.001 0.68 NS NS Urea, mg/dL 44.16a 36.80b 33.28b 33.61b 32.17b 37.12b 1.85 31.90c 33.60bc 36.39b 42.88a 1.39 <0.001 <0.001 0.20 *** *** Energy, MJ/kg4 4.50b 4.67ab 4.73ab 4.73ab 4.88a 4.73ab 0.06 5.18a 4.61b 4.56b 4.47b 0.05 <0.01 <0.001 0.90 *** * 1Treatment 1 through 6: the calculated average SID Lys content for the dietary treatment fed to sows in the given treatment group of the 71-sow data set. 2P-values for the dietary treatment (Trt) and DIM are from the ANOVA test using the MIXED procedure of SAS. The greatest SEM values within diets or within DIM are reported. 3Orthogonal polynomial contrasts were used to evaluate linear (lin) and quadratic (quad) effects of SID Lys: NS = not significant, † < 0.10, * < 0.05, *** < 0.001. 4Gross energy of milk was estimated, using the equation: GE (MJ/kg) = (38.9, MJ/kg × milk fat, % + 23.8, MJ/kg × milk protein, % + 16.3, MJ/kg × lactose, %)/100%, given by Chwalibog (2006). a–cWithin a row, values without common superscript letters differ (P < 0.05). Open in new tab Figure 5. Open in new tabDownload slide The effect of increasing standardized ileal digestible (SID) Lys on (A) milk fat, (B) milk DM, (C) milk energy, and (D) milk urea. The breakpoints are presented together with SEM and the P-values for the slopes above or below the breakpoints are presented. (A) Milk fat was best described by 1-slope linear broken-line models; Yi = 8.32DIM3 or 6.98DIM10 or 6.93DIM17 or 6.38DIM24 − 0.49 × (7.80 − Xi) for Xi < 7.80. Milk fat increased until a breakpoint of 7.80 ± 0.36 g/kg of SID Lys reaching 8.32, 6.98, 6.93, and 6.38% at 3, 10, 17, and 24 DIM (P < 0.05), respectively. (B) Milk DM was best described by 1-slope linear broken-line models; Yi = 19.3DIM3 or 17.7DIM10 or 17.6DIM17 or 17.3DIM24 − 0.49 × (7.81 − Xi) for Xi < 7.81. Milk DM increased until a breakpoint of 7.81 ± 0.51 g/kg of SID Lys reaching 19.3, 17.7, 17.6, and 17.3% at 3, 10, 17, and 24 DIM (P = 0.06), respectively. (C) Milk energy was best described by 1-slope linear broken-line models; Yi = 5.35DIM3 or 4.69DIM10 or 4.65DIM17 or 4.52DIM24 − 0.20 × (7.66 − Xi) for Xi < 7.66. Milk energy increased until a breakpoint of 7.66 ± 0.29 g/kg of SID Lys reaching 5.35, 4.69, 4.65, and 4.52 MJ/kg at 3, 10, 17, and 24 DIM (P < 0.01), respectively. (D) Milk urea was best described by 2-slope linear broken-line models; Yi = 28.6DIM3 or 29.4DIM10 or 32.7DIM17 or 39.5DIM24 + 10.8 × (7.33 − Xi) for Xi < 7.33 and + 1.22 × (Xi − 7.33) for Xi > 7.33. Milk urea decreased (P < 0.05) until a breakpoint of 7.33 ± 0.22 g/kg of SID Lys reaching 28.6, 29.4, 32.7, and 39.5 mg/dL at 3, 10, 17, and 24 DIM, respectively, and thereafter, it increased slightly at greater SID Lys levels (P = 0.23). The value, Xi, is the concentration of SID Lys, g/kg, for the individual sow, i. The least squared means from the ANOVA test are plotted as the given symbols, whereas the fitted models from the NLmixed procedure are plotted as the given lines. Figure 5. Open in new tabDownload slide The effect of increasing standardized ileal digestible (SID) Lys on (A) milk fat, (B) milk DM, (C) milk energy, and (D) milk urea. The breakpoints are presented together with SEM and the P-values for the slopes above or below the breakpoints are presented. (A) Milk fat was best described by 1-slope linear broken-line models; Yi = 8.32DIM3 or 6.98DIM10 or 6.93DIM17 or 6.38DIM24 − 0.49 × (7.80 − Xi) for Xi < 7.80. Milk fat increased until a breakpoint of 7.80 ± 0.36 g/kg of SID Lys reaching 8.32, 6.98, 6.93, and 6.38% at 3, 10, 17, and 24 DIM (P < 0.05), respectively. (B) Milk DM was best described by 1-slope linear broken-line models; Yi = 19.3DIM3 or 17.7DIM10 or 17.6DIM17 or 17.3DIM24 − 0.49 × (7.81 − Xi) for Xi < 7.81. Milk DM increased until a breakpoint of 7.81 ± 0.51 g/kg of SID Lys reaching 19.3, 17.7, 17.6, and 17.3% at 3, 10, 17, and 24 DIM (P = 0.06), respectively. (C) Milk energy was best described by 1-slope linear broken-line models; Yi = 5.35DIM3 or 4.69DIM10 or 4.65DIM17 or 4.52DIM24 − 0.20 × (7.66 − Xi) for Xi < 7.66. Milk energy increased until a breakpoint of 7.66 ± 0.29 g/kg of SID Lys reaching 5.35, 4.69, 4.65, and 4.52 MJ/kg at 3, 10, 17, and 24 DIM (P < 0.01), respectively. (D) Milk urea was best described by 2-slope linear broken-line models; Yi = 28.6DIM3 or 29.4DIM10 or 32.7DIM17 or 39.5DIM24 + 10.8 × (7.33 − Xi) for Xi < 7.33 and + 1.22 × (Xi − 7.33) for Xi > 7.33. Milk urea decreased (P < 0.05) until a breakpoint of 7.33 ± 0.22 g/kg of SID Lys reaching 28.6, 29.4, 32.7, and 39.5 mg/dL at 3, 10, 17, and 24 DIM, respectively, and thereafter, it increased slightly at greater SID Lys levels (P = 0.23). The value, Xi, is the concentration of SID Lys, g/kg, for the individual sow, i. The least squared means from the ANOVA test are plotted as the given symbols, whereas the fitted models from the NLmixed procedure are plotted as the given lines. Discussion Lys is the first limiting amino acid in lactation diets for sows (Danielsen, 1992; NRC, 2012) and therefore it is crucial to evaluate the Lys requirement. Based on the Danish recommendations per NE basis (Tybirk et al., 2017), diet 1 was deficient in Lys (74%), whereas diet 6 supplied dietary Lys in excess (117%) of the recommended concentration (8.32 g/kg of SID Lys; Table 3). The 6 dietary treatments were formulated to contain identical and adequate levels (102% or more) of SID Met, Met + Cys, Thr, Trp, Ile, Leu, His, Phe, Phe + Tyr, and Val per NE basis according to the current Danish recommendations (Tybirk et al., 2017). Thereby the criteria suggested by the NRC (2012) to study an amino acid requirement were fulfilled. Under current conditions (temperate climate, high-yielding sows, and fixed feeding curve) the dietary SID Lys required to maximize litter ADG was estimated to 8.11 g/kg of SID Lys (as-fed) and hence agreed fairly well with the previously recommended level (8.32 g/kg of SID Lys; Tybirk et al., 2017). The feed analyzes revealed that some amino acids were provided slightly below the recommended level in the low-Lys diet (diet 1; Val 99%, Met 96%, Met + Cys 96%, and Thr 95%) and in the high-Lys diet (diet 6; His 99%, Val 99%, Met 98%, Met + Cys 97%, and Thr 94%), and these amino acids were, unfortunately, marginally more deficient than Lys in diet 4 through 6 (Table 3). The most pronounced undersupply was caused by Thr, which was included at 95% of the recommended level (Tybirk et al., 2017) in the breakpoint for litter ADG (8.11 g/kg of SID Lys). One may argue that Thr did slightly limit the milk production as it was supplied 5% below the Danish recommendation and consequently, Lys and Thr were most likely co-limiting in the breakpoint for litter ADG. However, it is important to emphasize that traits like the litter ADG respond according to the “law of diminishing returns,” which means that a 5% undersupply in Thr only marginally reduced the ADG of the litter. In line with that, the achieved litter ADG was indeed very high and greater than in previous dose-response trials carried out in the same herd (Strathe et al., 2016, 2017; Hojgaard et al., 2019a, 2019b). The approach of increasing the dietary SID Lys supply while keeping all other amino acids constant to estimate the SID Lys required to maximize litter gain altered the amino acid ratios relative to Lys. Therefore, the lack of response on litter ADG above the optimal level (8.11 g/kg of SID Lys) could indicate that 1 or more other amino acids became co-limiting. However, when Lys is supplied in excess (as was the case for diet 4, 5, and 6 in the present study), it makes no sense to compare other amino acids relative to Lys because the derived amino acid ratios relative to Lys do not represent the ratio utilized by the sow (excess Lys will reduce the amino acid to Lys ratios, but not the “effective ratio,” which may be calculated by using the Lys concentration in the breakpoint). In such a case it is necessary to evaluate whether the recommended levels were met for each amino acid relative to energy or per kg feed, instead of evaluating the ratio relative to Lys. The estimated intake of dietary Lys in the breakpoint for litter ADG was 53.5 and 60.6 g/d of total Lys or 47.7 and 54.1 g/d of SID Lys for primi- and multiparous sows, based on ADFI of 5.88 and 6.66 kg/d, respectively. Recently, Strathe et al. (2017) investigated the effect of increasing dietary CP. Litter growth was maximized to 2.53 and 3.07 kg/d at 135 g/kg of SID CP corresponding to approximately 8 g/kg of SID Lys and approximately 51 g/d of SID Lys (parity 1 to 4 sows). This agrees fairly well with the current study even though the sows in the study by Strathe et al. (2017) received mainly protein bound Lys. In the latter study it remained unknown whether the observed breakpoint for SID CP was indeed driven by the increase in SID CP or the increase in SID Lys. The optimal dietary SID Lys level in current study indicates that the previous breakpoint of SID CP at 135 g/kg (approximately 8 g/kg of SID Lys; Strathe et al., 2017) most likely was driven by the increase in dietary Lys rather than the increase in dietary CP. According to NRC (2012), the calculated SID Lys required to maximize litter gain in the current study would be 53.1 and 58.5 g/d for primi- and multiparous sows, respectively. Thus, our results agree fairly well with NRC (2012) even though studies with litter growth rates greater than 2.3 kg/d were not included in the latter. Interestingly, NRC assumes a Lys efficiency of 67%, whereas in the current study we calculate an efficiency of converting dietary Lys to milk Lys amounting to 88% (based on the assumption that milk contains 7.01 g of Lys per 100 g milk CP; NRC, 2012). This suggests that NRC underestimates the sow milk yield as compared with estimation based on Hansen et al. (2012), whereas similar efficiencies are found when converting dietary SID Lys into litter ADG. Our reported values for daily Lys requirement also agree with 48.7 and 53.3 g SID Lys, for primi- and multiparous sow, respectively, as calculated from the InraPorc model (Dourmad et al., 2008). The daily SID Lys required per kg of litter gain and per kg of milk yield were estimated by regressing these traits on daily SID Lys intake of the 66 sows fed diet 4 (i.e., the sows fed slightly above the optimal SID Lys level of 8.11 g/kg; data not shown). The dietary SID Lys required per kg of litter ADG and per kg of milk yield amounted to approximately 16 and 4.0 g/d, respectively, regardless of sow parity (primi- vs. multiparous). These estimates agree very well with the rule of thumb saying that approximately 4 kg of milk is required to produce 1 kg of litter gain (Whittemore and Morgan, 1990). Loss of body protein was ignored because sows only lost 0.61 kg from day 3 to 26 in lactation when fed diet 4, corresponding to approximately 27 g/d. Assuming that body protein contains 6.74% of Lys (NRC, 2012), mobilization of body protein corresponded to 2 g/d of mobilized Lys. Based on studies from 1972 to 1997, Pettigrew (1993) developed a response curve, where the slope indicated that 26 g of dietary Lys was needed daily per kg of litter weight gain, corresponding to 22 g/d of SID Lys per kg of litter weight gain assuming a standard ileal digestibility of 85%. Seven years later, Boyd et al. (2000) updated this equation to include Lys studies published between 1993 and 1997 and concluded that 27 g/d of total dietary Lys was needed per kg of litter gain, and recently, Tokach et al. (2019) made further updates by inclusion of studies published between 2000 and 2017. The new response curve reported by Tokach et al. (2019) revealed that 27 g/d of SID Lys per kg of litter gain was required. Applying that estimate to our sows, litter growth rates of 2.93 and 3.36 kg/d for primi- and multiparous sows would require an intake of 66.1 and 77.7 g/d of SID Lys, respectively. This is much greater than what we estimated in the current study. In the new regression from Tokach et al. (2019), however, results from Xue et al. (2012) and Gourley et al. (2017) were included and they concluded that mixed parity sows require approximately 55 g/d of SID Lys for a litter growth of 2.40 and approximately 70 g/d of SID Lys for a litter growth of 2.9 kg/d, respectively. Different from this study was that great amounts of corn (approximately 64%) were included in their experimental diets as the primary source of starch. Corn protein has a great content of Leu (approximately 11% of CP) compared to wheat (approximately 6.5% of CP) and barley (approximately 6.9% of CP) which are the primary sources of starch in Danish feed formulations. Inclusion of great amounts of corn in combination with the use of soybean meal to meet minimum requirements of essential amino acids often results in SID Leu to Lys ratios of approximately 163% (Zhang et al., 2019), whereas the Danish recommendation of Leu is at 108% relative to Lys (Tybirk et al., 2017) and the NRC recommendation is at 114% (NRC, 2012). Previously, Guan et al. (2004) and Manjarin et al. (2012) suggested that there is competition among branched-chain amino acids (Ile, Leu, and Val) and Lys when these amino acids are taken up by the mammary glands, in particular between Leu and Lys, which may affect the utilization of Lys for milk production. Recent work by Zhang et al. (2019) demonstrated that litter ADG at peak lactation was greater in sows fed a diet containing an SID Leu to Lys ratio of 114% (i.e., close to the Danish recommendation) as compared with sows fed a diet containing an SID Leu to Lys ratio of 163% (reflecting a corn-based sow diet). Therefore, it can be argued that models based on studies containing high concentrations of Leu from corn may overestimate the Lys requirement for lactating sows when applied to sows fed common European diets based mainly on wheat and barley. The ADFI must also be considered when the requirement is expressed as a concentration of the diet to evaluate whether the SID Lys required to maximize litter ADG was covered by a given diet (Strathe et al., 2015). It is well known that primiparous sows generally have a lower voluntary feed intake than multiparous sows (Eissen et al., 2000) and also a lower milk production (Strathe et al., 2017; Hojgaard et al., 2019b). Consequently, primiparous sows have a lower daily Lys requirement than multiparous sows. In the current experiment there was no difference in Lys requirements for multiparous and primiparous sows when expressed as a concentration of the diet because primiparous sows were allowed a lower feed curve than multiparous sows. Primiparous sows consumed 0.78 kg feed less daily than multiparous sows corresponding to approximately 6 g/d of SID Lys. However, primiparous sows also produced 0.43 kg/d of litter ADG less than multiparous sows which also corresponded to a lower requirement amounting to approximately 6 g/d of SID Lys. Consequently, the lower feed curve applied to primiparous sows fulfilled their requirement for SID Lys at the same breakpoint for primi- and multiparous sows. Besides feed intake, it is also worth considering climate, genotype, and differences in performance. This study was conducted in a rather temperate climate, with high-producing sows, which is not always the case because most sows worldwide are not as high producing as Danish sows and the feed intake of sows may also be compromised considerably if kept in tropical climate. Thus, the SID Lys required to maximize litter ADG in current study was based on Danish conditions but will need to be adapted to other regions by considering differences in performance and feed intake. Sow BW loss was minimized at a greater dietary SID Lys concentration than that required to maximize litter growth. Indeed, lactating sows required 9.05 g/kg of SID Lys to minimize sow BW loss, corresponding to 53.2 and 60.3 g/d of SID Lys for primi- and multiparous sows, respectively. This agrees with the loss of body protein tissues which was minimized at 9.22 g/kg of SID Lys. Previous literature also reported that a greater Lys intake is needed to minimize body protein loss than to maximize litter gain because sows mobilize body protein reserves to support milk production (King et al., 1993; Touchette et al., 1998; Huang et al., 2013; Strathe et al., 2017). However, sow body protein mobilization could not fully compensate the dietary Lys deficiency below the breakpoint of maximum litter gain of 8.11 g/kg of SID Lys. The formation of urea nitrogen usually increases due to catabolism of excess nitrogen, which in this study originates from imbalance in the dietary amino acid profile. At low levels of dietary Lys, PUN increased, because dietary Lys was insufficiently supplied. Even though body protein was mobilized to supply extra Lys, 19 other amino acids were most likely oxidized. A slight increase in PUN with further increase in dietary Lys above the optimal concentration would not have been surprising due to the oversupply of Lys solely. In line with that, urea nitrogen in milk increased slightly at greater levels of SID Lys which may be due to net mammary uptake of PUN or mammary synthesis of urea (Krogh et al., 2017). Results from an ex vivo study by Hurley et al. (2000) indicated that a small but significant amount of Lys utilized by lactating sow mammary tissue was oxidized, which supported that Lys oxidation potentially could raise urea in milk. Furthermore, other amino acids, especially branched-chain amino acids (Ile, Leu, and Val) supplied in excess are oxidized or metabolized by sow mammary tissue for purposes other than protein synthesis. Possibly mammary metabolism of amino acids occurs to deliver carbon and nitrogen for de novo synthesis of lactose, fatty acids, and nonessential amino acids, and involves recirculation of great amounts of, e.g., alanine to the liver (Kristensen and Wu, 2012). Plasma urea nitrogen is considered a valid response criterion to determine amino acid requirements when the protein intake is constant and the amino acid of interest is the only variable (Coma et al., 1995). Plasma urea nitrogen reached a plateau at 7.02, 8.10, 8.73, and 8.10 g/kg of SID Lys at 3, 10, 17, and 24 DIM, respectively. The changes in SID Lys required in early, peak, and late lactation to minimize PUN supports that the Lys requirement follow the lactation curve, i.e., lowest in week 1, intermediate in week 2 and 4, and greatest in week 3 of lactation (Hansen et al., 2012; Strathe et al., 2015). This could indicate that feeding a single lactation diet at the optimal level (8.11 g/kg of SID Lys) may supply excess dietary Lys in week 1, adequate in week 2 and 4, but insufficient Lys in week 3 of lactation. This contradicts a previous idea that lactation diets should be more concentrated in early lactation to fulfill nutrient requirements because of a lower feed intake capacity in early lactation than in late lactation (Strathe et al., 2015). During week 1 of lactation, regression of the uterus releases amino acids that become available for milk production (Dourmad et al., 1998; Feyera and Theil, 2017). Released uterine Lys may contribute to lower the dietary SID Lys requirement in week 1 which was also predicted by Gauthier et al. (2019) using an individual-based model. In week 3 of lactation, the PUN concentration strongly suggested that dietary Lys will limit the milk production even if sows are fed with 8.11 g/kg of SID Lys. Under the conditions in current study where sows, however, were restricted in their feed intake, this finding may indicate that the requirement for SID Lys cannot be matched perfectly using a single-diet strategy throughout lactation which is the most common strategy today because most commercial farms do not have a feeding system in the farrowing unit that can handle 2 or more diets. In the future, more advanced feeding systems that allow a more dynamic feeding strategy throughout lactation should be considered. However, more research is needed to evaluate optimal dietary ratios of other amino acids than Lys at different stages of lactation and different requirements depending on BW (or parity) as discussed by Gauthier et al. (2019). The plasma concentration of NEFA is a common measure of fat catabolism (Mejia-Guadarrama et al., 2002). Plasma NEFA increased until a breakpoint of 7.5 g/kg of SID Lys and thereafter decreased with further increase in dietary Lys. This is in line with the BF loss which responded quadratically to increasing dietary Lys, though without being able to detect a breakpoint. The greater concentration of plasma NEFA close to the breakpoint for litter average daily gain is most likely because the optimal dietary Lys supply stimulated the sows to produce more milk. Because all sows were fed the same amount of energy, the highest producing and most optimally fed sows were in more negative energy balance, illustrated by the greatest NEFA concentration. This increased the fat and energy concentrations of milk which agrees with previous findings (Strathe et al., 2017; Hojgaard et al., 2019b). Furthermore, plasma concentrations of NEFA not only derive from fat mobilization but also from net release by the mammary glands at 1.5 to 3.5 h after feeding (Krogh and Theil, 2017). The study by Krogh and Theil (2017) suggested that the mammary glands produce NEFA when plasma nutrients are abundantly available after feeding and the de novo produced NEFA is being net released from the mammary glands to plasma, which then act as a buffer system for NEFA. Later in the postprandial period, plasma NEFA will then return to the mammary glands when plasma nutrients again become scarcely available during the postprandial period (i.e., more than 4 h after feeding). Subsequent reproduction performance was not affected by the investigated dietary Lys levels despite mobilization of body protein increased at lower dietary Lys levels. However, Clowes et al. (2003a, 2003b) stated that over a 4-wk lactation period up to 9 to 12% of the sows’ protein mass at parturition could be lost without detrimental effects on subsequent reproduction. Based on the broken-line model for sow body protein loss, sows in the current study lost 2.3 kg of body protein when receiving the lowest level of SID Lys (6.27 g/kg). This corresponds to a loss of 5.4% of the sows’ day 3 body protein mass and may explain the lack of an influence of dietary Lys intake during lactation on reproduction performance in subsequent cycle. Furthermore, modern genotype sows seem to be more resilient to the effects of lactational catabolism as reviewed by Tokach et al. (2019). Interestingly, the mobilization of body fat throughout lactation is as high as 11 to 12 kg for sows when fed optimally with Lys and this indicates that supplying adequate energy is even more challenging now for high-producing sows when supplied adequate dietary Lys. Conclusion In our conditions, high-yielding lactating sows require 8.11 g/kg of SID Lys to maximize litter gain and 9.05 g/kg of SID Lys to minimize sow BW loss. 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TI - Optimal lysine in diets for high-yielding lactating sows
JF - Journal of Animal Science
DO - 10.1093/jas/skz286
DA - 2019-10-03
UR - https://www.deepdyve.com/lp/oxford-university-press/optimal-lysine-in-diets-for-high-yielding-lactating-sows-USC44ITaG4
SP - 4268
VL - 97
IS - 10
DP - DeepDyve
ER -