TY - JOUR AU - Lafrenière, C. AB - ABSTRACT Forty Angus-cross steers were used to evaluate 5 beef cattle management regimens for their effect on growth performance, carcass characteristics, and cost of production. A 98-d growing phase was incorporated using grass silage with or without growth promotants (trenbolone acetate + estradiol implants, and monensin in the feed) or soybean meal. Dietary treatments in the finishing phase were developed, with or without addition of the same growth promotants, based on exclusive feeding of forages with minimal supplementation or the feeding of barley-based diets. Overall, ADG for animals treated with growth promotants or fed supplemented diets (soybean meal and barley) was increased (P < 0.01) by 25 and 21%, respectively, compared with steers reared on grass silage alone and not treated with growth promotants. Except for HCW (P < 0.01), the use of growth promotants did not affect carcass measurements. Increasing the proportion of barley in the diet of steers finished on forage produced a heavier HCW (P < 0.01) and a greater (P < 0.01) quality grade. Because of their lower HCW and quality grade, cattle targeted to a forage-fed, nonimplanted beef market would need to garner a 16% premium to be economically competitive with cattle finished conventionally. INTRODUCTION The use of ionophores and hormonal implants is common in North American feedlots. However, consumer surveys (Bérubé, 2002) have shown that use of growth promotants in beef production is considered a risk for human health by 76% of consumers interviewed. Forage-fed, “natural” beef (i.e., produced without the use of ionophores and hormonal implants) could be an alternative to satisfy this market niche. Research has shown that early maturing cattle (Hereford × Shorthorn) can be finished on grass silage to achieve satisfactory quality grades and produce beef with similar palatability attributes as grain-fed beef (Fortin et al., 1985). Moreover, forage finishing of continental breeds (Charolais, Limousin) produced carcasses that satisfied the tenderness demands of consumers, albeit with different flavor intensities vs. grain-fed beef (Mandell et al. 1997, 1998). In all of the previously cited studies, cattle received growth promotants. Fernández and Woodward (1999) compared organic vs. conventional beef production and concluded that organic beef would cost 39% more, mainly because of lower animal performance and the greater cost of organically produced feedstuffs. Differences in ADG and G:F were likely due to the absence of growth promotants in the organic production system. Sawyer et al. (2003) evaluated the costs of finishing programs with or without growth promotants and concluded that cattle targeted for niche markets requiring the abandonment of hormonal implants and antimicrobials would need to garner a price premium of $44 US to be competitive with conventional beef. It is imperative to determine the impact of not using growth promotants on costs of production and quality of forage-fed beef to provide the beef industry with research-based information for producers to make the best decisions on alternative production systems. Therefore, our objective was to evaluate forage vs. grain finishing with or without the use of growth promotants on growth performance, costs of production, and carcass characteristics. MATERIALS AND METHODS Animals, Diets, and Experimental Design This experiment was conducted at the Kapuskasing Beef Research Farm in Northern Ontario between January and October 2002. All experimental procedures performed in this study were approved by the institutional animal care committee based on the current guidelines of the Canadian Council on Animal Care (1993). A total of 40 Angus cross steer calves (approximately 8 mo of age) were purchased from Saskatchewan and transported to Kapuskasing. Upon receipt, steers were vaccinated for infectious bovine rhinotratracheitis, bovine viral diarrhea, parainfluenza 3, and bovine respiratory syncytial virus (Triangle 4, Wyeth Animal Health, Guelph, ON), administered a 7-way clostridial bacterin (Covexin 8, Schering-Plough Animal Health, Pointe Claire, QC), and treated for internal and external parasites (Cydectin, Wyeth Animal Health, Guelph, ON). The 40 animals were assigned to 5 groups, with the 5 management regimens (Table 1) distributed at random within each of these groups. Steers were then placed in 5 pens within an unheated, but insulated, enclosed feedlot. Each pen was equipped with electronic head-gates to allow individual measurement of feed intake. Before initiation of the study, steers were allowed to adapt to the feed and the electronic headgates for 21 d. During this period, steers were fed only grass silage and a mineral supplement once daily. Also, during the first 14 d of this period, animals in treatments grass silage + growth promotant (GS/GP) and GS/GP + 8% soybean meal (GS/GP HCON) were given the adaptation dose (11 mg of DM/kg) of monensin (Rumensin, Elanco, Division Eli Lilly Canada Inc., Guelph, ON). After that period, the dose was increased to 33 mg of DM/kg for the duration of the study. Table 1. Feedlot management regimens and treatments applied during the growing and finishing phases Management regimen Treatment applied during specific feeding phases Growing phase (d 0 to 98) GS Grass silage only GS/GP1 Grass silage fed with growth promotants GS + LCON2 Grass silage + 4% soybean meal GS + HCON3 Grass silage + 8% soybean meal GS/GP + HCON Grass silage + 8% soybean meal + growth promotants Finishing phase (d 99 to slaughter) GS Grass silage only GS/GP4 Grass silage fed with growth promotants GS + LCON Grass silage + 40% rolled barley GS + HCON Grass silage + 70% rolled barley GS/GP + HCON Grass silage + 70% rolled barley + growth promotants Management regimen Treatment applied during specific feeding phases Growing phase (d 0 to 98) GS Grass silage only GS/GP1 Grass silage fed with growth promotants GS + LCON2 Grass silage + 4% soybean meal GS + HCON3 Grass silage + 8% soybean meal GS/GP + HCON Grass silage + 8% soybean meal + growth promotants Finishing phase (d 99 to slaughter) GS Grass silage only GS/GP4 Grass silage fed with growth promotants GS + LCON Grass silage + 40% rolled barley GS + HCON Grass silage + 70% rolled barley GS/GP + HCON Grass silage + 70% rolled barley + growth promotants 1 Growth promotants includes feeding of Rumensin (Elanco Division, Eli Lilly Canada Inc., Guelph, ON) and implanting with Revalor G (Hoechst-Roussel Agri-Vet, Somerville, NJ). 2 LCON = low levels of supplementary concentrates fed. In the growing phase, LCON was the addition of 4% soybean meal to the diet, whereas in the finishing phase, LCON was the addition of 40% rolled barley to the diet. 3 HCON = high levels of supplementary concentrates fed. In the growing phase, HCON was the addition of 8% soybean meal to the diet, whereas in the finishing phase, HCON was the addition of 70% rolled barley to the diet. 4 Growth promotants included feeding of Rumensin (Elanco) and implanting with Revalor S (Hoechst-Roussel Agri-Vet). View Large Table 1. Feedlot management regimens and treatments applied during the growing and finishing phases Management regimen Treatment applied during specific feeding phases Growing phase (d 0 to 98) GS Grass silage only GS/GP1 Grass silage fed with growth promotants GS + LCON2 Grass silage + 4% soybean meal GS + HCON3 Grass silage + 8% soybean meal GS/GP + HCON Grass silage + 8% soybean meal + growth promotants Finishing phase (d 99 to slaughter) GS Grass silage only GS/GP4 Grass silage fed with growth promotants GS + LCON Grass silage + 40% rolled barley GS + HCON Grass silage + 70% rolled barley GS/GP + HCON Grass silage + 70% rolled barley + growth promotants Management regimen Treatment applied during specific feeding phases Growing phase (d 0 to 98) GS Grass silage only GS/GP1 Grass silage fed with growth promotants GS + LCON2 Grass silage + 4% soybean meal GS + HCON3 Grass silage + 8% soybean meal GS/GP + HCON Grass silage + 8% soybean meal + growth promotants Finishing phase (d 99 to slaughter) GS Grass silage only GS/GP4 Grass silage fed with growth promotants GS + LCON Grass silage + 40% rolled barley GS + HCON Grass silage + 70% rolled barley GS/GP + HCON Grass silage + 70% rolled barley + growth promotants 1 Growth promotants includes feeding of Rumensin (Elanco Division, Eli Lilly Canada Inc., Guelph, ON) and implanting with Revalor G (Hoechst-Roussel Agri-Vet, Somerville, NJ). 2 LCON = low levels of supplementary concentrates fed. In the growing phase, LCON was the addition of 4% soybean meal to the diet, whereas in the finishing phase, LCON was the addition of 40% rolled barley to the diet. 3 HCON = high levels of supplementary concentrates fed. In the growing phase, HCON was the addition of 8% soybean meal to the diet, whereas in the finishing phase, HCON was the addition of 70% rolled barley to the diet. 4 Growth promotants included feeding of Rumensin (Elanco) and implanting with Revalor S (Hoechst-Roussel Agri-Vet). View Large The 5 management regimens each included separate growing (d 0 to d 98) and finishing (d 99 to slaughter) phase treatments. These regimens were based on feeding a grass silage diet that was minimally supplemented (mineral mix only) or supplemented with varying amounts of barley over the course of the experiment. Silage was made between June 17 and June 21 from the primary growth of a mixed grass sward containing orchardgrass (Dactylis glomerata), quackgrass (Agro-pyron repens), and weeds (70:20:10 by visual assessment). The forages were cut with a mower-conditioner and picked up within 6 h with a precision harvester adjusted to a theoretical chop length of 9 mm. Formic acid (85%) was applied at approximately 2.5 kg/1,000 kg of fresh material as it was placed in the silo. Silage was made in 3 bunk silos with the walls and exposed surfaces of the silage being covered with plastic sheets. Growing Phase. On d 0 of the study, steers were introduced to their respective diets (Table 1). The treatments were grass silage only (GS), GS/GP, GS + 4% soybean meal (GS + LCON), GS + HCON, and GS/GP + HCON. Animals assigned to treatments GS/GP and GS/GP + HCON were implanted with Revalor G (40 mg of trenbolone acetate + 8 mg of estradiol; Hoechst-Roussel Agri-Vet, Somerville, NJ). The same steers were reimplanted 70 d later with Revalor S (120 mg of trenbolone acetate + 24 mg of estradiol; Hoechst-Roussel Agri-Vet). During the growing phase, steers on all dietary treatments had ad libitum access to grass silage. Animals on treatments GS + LCON, GS + HCON, and GS/GP + HCON were supplemented with solvent-extracted soybean meal at 4% (treatment GS + LCON) or 8% of the diet (treatments GS + HCON and GS/GP + HCON). The total mixed ration was fed once daily (0900) at an estimated 110% of the previous day ad libitum intake. Water was continuously available. The quantity of feed placed before every steer and the quantity left uneaten were weighed daily. Finishing Phase. After weighing steers on d 98, the diets of steers on treatment GS + LCON, GS + HCON, and GS/GP + HCON were gradually changed to energy-dense diets. Animals on treatment GS + LCON were offered a total mixed ration composed of grass silage and rolled barley (60:40, DM basis), whereas steers on treatments GS + HCON and GS/GP + HCON were offered a total mixed ration composed of grass silage and rolled barley (30:70, DM basis). Cattle were adjusted gradually to grain-based diets by offering 75% silage and 25% barley for 7 d followed by 60% silage and 40% barley for 4 d. Thereafter, the proportion of barley was increased by 10% every 4 d until it reached 80% of the diet DM. However, when barley was increased from 70 to 80%, steers on treatment GS + HCON, which received no ionophores, reduced their voluntary intake and exhibited signs of rumen acidosis. As soon as the proportion of barley was reduced to 70%, all animals resumed eating. It was therefore decided to limit barley to 70% of the diet (DM basis). The total mixed ration was fed once daily (0900) at an estimated 110% of ad libitum intake. Water was continuously available. The quantity of feed placed before every steer and the quantity left uneaten were weighed daily. To mimic conditions in a commercial feedlot, no animals were slaughtered before they had deposited at least 8 mm of backfat (measured by ultrasound) at the ³/3 position over the LM at the last rib. This backfat thickness has been shown to yield Canada A grade carcasses in previous trials (Veira et al., 1983; Petit and Flipot, 1992; Petit et al., 1994). Ultrasound determinations of backfat were conducted every 14 d when half of the steers had deposited 6 mm. Animals were weighed and jugular blood samples were collected after a 24-h fast and 12 h without water, and 24 h before transportation to the abattoir. After the final weighing, steers were given access to water, a mixture of electrolytes (1 kg/steer; Nutri-Charge, Research Management Services, Edmonton, AB) and feed. Steers were transported more than 900 km to an abattoir near Sherbrooke, QC. One group (n = 11) was shipped on d 182, 1 group (n = 14) on d 205, 1 group (n = 9) on d 238, and a final group (n = 6) was transported to the abattoir on d 268. Carcass Quality Measurements After slaughter, HCW was recorded before overnight chilling at 1°C, and the carcass yield was calculated based on the departure weight at the farm. Six days after slaughter, which corresponds to the normal aging period before grading of carcasses sold in Quebec (B. Doré, Federation of Beef Producers of Quebec, Longueuil, Canada, personal communication), carcasses were graded by a single grader according to the Livestock and Poultry Carcass Grading Regulations (Canadian Food Inspection Agency, 1992). The interface between the 12th and 13th ribs was used to obtain the following carcass measurements: subcutaneous fat thickness (mm) at ¼, ½, and ¾ positions over the LM (beginning from the medial side); grade fat or minimum fat (mm) in the last quadrant over the LM (from the ¾ position to the end of the lateral side); LM area (cm2; determined directly from tracings of the LM in the rib-eye); yield grade (cutability, %), or lean yield, (expected yield of trimmed, defatted lean from the major wholesale cuts in the carcass) as measured using the Canadian Beef Grading Agency (Agriculture Canada, 1992) grade ruler; subjective score for color of the lean using a 5-point scale (from 1 = very dark to 5 = very light cherry); subjective score for fat color using a 5-point scale (from 1 = lemon yellow to 5 = white); marbling scores using: a) the USDA (USDA, 1989) 10-point scale (1 = devoid to 10 = abundant marbling), and b) the 5 associated quality grades based on marbling deposition (Agriculture Canada, 1992) including Canada B1 (devoid = marbling score 1 to 2), A (trace = marbling score 3), AA (slight = marbling score 4), AAA (small = marbling score 5 to 7), and AAAA (prime = marbling score = 8 to 9). Cost of Production All costs were individually calculated for the period of time that each steer was on feed. Feed costs were calculated as the price paid for the feed times the amount of feed consumed, except for grass silage, which was estimated to cost $100/t of DM. Prices paid were $350/t for soybean meal and $197/t for rolled barley. The cost of mineral varied among treatments, depending on the quantity ingested, the ingredients, and the presence of an ionophore. The price paid for the monensin premix (Rumensin200, Elanco Division, Eli Lilly Canada Inc., Guelph, ON) was $19.80/kg. Yardage was calculated as the sum of implants ($1.85/steer in growing phase; $4.67/steer in the finishing phase), veterinary costs (antibiotics, anthelmintics, and veterinary fees; $9.80/steer), labor ($10/h), fixed costs (building maintenance and insurance; $7.36/steer), and interest (6.5% per annum × number of days on feed). Purchase price for feeders was $2.64/kg. Chemical Analyses Dry matter of silage samples was determined by lyophilization, whereas oven drying at 100°C was used to measure DM of soybean meal and barley. As-fed samples of silage were soaked with water (2:1, wt:vol) and used for pH determination with a glass electrode. Total N in silage, soybean meal, and barley was determined according to the AOAC (1980). Ammonia, lactic acid, and VFA were determined on an aliquot from the maceration of 20 g of as-fed silage in 200 mL of 0.01 N HCl. Aliquots for lactic acid and VFA were deproteinized using Dowex resin (50WX8, Sigma-Aldrich Canada, Oakville, ON). Concentrations of lactic acid and VFA were determined with an ionic HPLC equipped with an IonPac AS11-HC column (Dionex, DX-500, Dionex Canada, Oakville, ON). Peaks were separated using a gradient mode with an eluent flow of 1.50 mL/min with an initial ratio of 80:20 of deionized water: 5 mM NaOH during the first 10 min followed by a period of 8 min to reach a final ratio of 0:100. Peaks were integrated with Peaknet 5.11 (Dionex Canada) using reference values. Ammonia was determined on a 25 mL aliquot by distillation over MgO as described by Flipot et al. (1976) on an automated Kjeltec 1030 (Foss, Eden Prairie, MN). Water soluble carbohydrates were measured colorimetrically (Dubois et al., 1956) on a 1-mL water extract using 0.1 g of silage soaked in 50 mL of deionized water and agitated for 1 h. Cell wall fractions (NDF, ADF, and ADL) were measured in oven-dried (55°C) samples according to Van Soest et al. (1991) using an Ankom200 Fiber Analyzer (Ankom, Macedon, NY). Nitrogen and residual N in ADF and NDF in oven-dried samples were determined by the Kjeldahl method according to method 7.022 of the AOAC (1990). Nitrogen fractions (NPN and soluble N) were determined according to the methods outlined by Licitra et al. (1996). Subsamples of feed were ashed at 600°C for 2 h in a muffle furnace to determine OM (method 7.009 in AOAC, 1990). Starch was determined on oven-dried samples milled to 250 μm using a starch kit (No. 10 207 748 035, Boehringer Mannheim, Burgessville, ON). Fat in silages was determined by the method outlined by Thiex et al. (2003), using hexane and a Soxtec Avanti 2050 (Foss) apparatus on a 3-g sample with an extraction phase of 20 min. For barley, the extraction phase was increased to 40 min, whereas for soybean meal a 2-g sample was used with an extraction phase of 40 min. Statistical Analysis The 5 treatments were allocated to calves according to a balanced incomplete block design. Five pens with 8 Calan gates per pen were divided into 2 sides with 4 Calan gates per side, giving 10 pen-side combinations (blocks). Each steer (n = 40) was considered an experimental unit. The statistical model included block as a random effect and treatment as a fixed effect. Four contrasts were used to evaluate the differences between the 5 treatments. Three factorial orthogonal contrasts were used to examine the main effects of growth promotants (GS, GS + HCON vs. GS/GP, GS/GP + HCON) and concentrates (GS, GS/GP vs. GS + HCON, GS/GP + HCON) and their interaction, and a fourth contrast compared treatments GS/GP vs. GS + LCON to determine if growth promotants (GS/GP) could be replaced by feeding moderate amounts of concentrates (GS + LCON) in the growing and finishing phase. For statistical analysis, the carcass grades were transformed to the numerical codes B = 1, A = 2, AA = 3, and AAA = 4. All analyses were carried out using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). RESULTS AND DISCUSSION Silage Composition The analyzed composition of silage, soybean meal, and barley are presented in Table 2. The concentrations of NDF, ADF, and ADL in the silages are indicative of forages of good to high quality. Moreover, values for pH (4.14 and 4.02), levels of total N in the form of NH3-N (39 and 47 g/kg), and ADIN (39 and 36 g/kg) indicate that both silages were well preserved. Table 2. Analyzed composition of feeds (DM basis) Item Silage fed during the growing phase Silage fed during the finishing phase Barley Soybean meal pH 4.12 4.04 DM, g/kg 305 255 888 908 Ash, g/kg of DM 94 94 26 63 NDF, g/kg of DM 525 529 116 95 ADF, g/kg of DM 326 335 71 42 ADL, g/kg of DM 43 47 12 2 Fat, g/kg of DM 30 35 6 8 Starch, g/kg of DM 3 2 420 42 CP, g/kg of DM 161 156 116 498 ADIN, g/kg of CP 39 36 NDIN,1 g/kg of CP 213 188 NH3-N, g/kg of CP 39 47 Soluble N, g/kg of CP 566 544 31 25 NPN, g/kg of Sol N 856 949 Lactic acid, g/kg of DM 41 54 Acetic acid, g/kg of DM 14 19 Propionic acid, g/kg of DM 1 2 Butyric acid, g/kg of DM 3 3 Isobutyric acid, g/kg of DM 7 9 Valeric acid, g/kg of DM 0.5 0.5 Item Silage fed during the growing phase Silage fed during the finishing phase Barley Soybean meal pH 4.12 4.04 DM, g/kg 305 255 888 908 Ash, g/kg of DM 94 94 26 63 NDF, g/kg of DM 525 529 116 95 ADF, g/kg of DM 326 335 71 42 ADL, g/kg of DM 43 47 12 2 Fat, g/kg of DM 30 35 6 8 Starch, g/kg of DM 3 2 420 42 CP, g/kg of DM 161 156 116 498 ADIN, g/kg of CP 39 36 NDIN,1 g/kg of CP 213 188 NH3-N, g/kg of CP 39 47 Soluble N, g/kg of CP 566 544 31 25 NPN, g/kg of Sol N 856 949 Lactic acid, g/kg of DM 41 54 Acetic acid, g/kg of DM 14 19 Propionic acid, g/kg of DM 1 2 Butyric acid, g/kg of DM 3 3 Isobutyric acid, g/kg of DM 7 9 Valeric acid, g/kg of DM 0.5 0.5 1 NDIN = neutral detergent insoluble N. View Large Table 2. Analyzed composition of feeds (DM basis) Item Silage fed during the growing phase Silage fed during the finishing phase Barley Soybean meal pH 4.12 4.04 DM, g/kg 305 255 888 908 Ash, g/kg of DM 94 94 26 63 NDF, g/kg of DM 525 529 116 95 ADF, g/kg of DM 326 335 71 42 ADL, g/kg of DM 43 47 12 2 Fat, g/kg of DM 30 35 6 8 Starch, g/kg of DM 3 2 420 42 CP, g/kg of DM 161 156 116 498 ADIN, g/kg of CP 39 36 NDIN,1 g/kg of CP 213 188 NH3-N, g/kg of CP 39 47 Soluble N, g/kg of CP 566 544 31 25 NPN, g/kg of Sol N 856 949 Lactic acid, g/kg of DM 41 54 Acetic acid, g/kg of DM 14 19 Propionic acid, g/kg of DM 1 2 Butyric acid, g/kg of DM 3 3 Isobutyric acid, g/kg of DM 7 9 Valeric acid, g/kg of DM 0.5 0.5 Item Silage fed during the growing phase Silage fed during the finishing phase Barley Soybean meal pH 4.12 4.04 DM, g/kg 305 255 888 908 Ash, g/kg of DM 94 94 26 63 NDF, g/kg of DM 525 529 116 95 ADF, g/kg of DM 326 335 71 42 ADL, g/kg of DM 43 47 12 2 Fat, g/kg of DM 30 35 6 8 Starch, g/kg of DM 3 2 420 42 CP, g/kg of DM 161 156 116 498 ADIN, g/kg of CP 39 36 NDIN,1 g/kg of CP 213 188 NH3-N, g/kg of CP 39 47 Soluble N, g/kg of CP 566 544 31 25 NPN, g/kg of Sol N 856 949 Lactic acid, g/kg of DM 41 54 Acetic acid, g/kg of DM 14 19 Propionic acid, g/kg of DM 1 2 Butyric acid, g/kg of DM 3 3 Isobutyric acid, g/kg of DM 7 9 Valeric acid, g/kg of DM 0.5 0.5 1 NDIN = neutral detergent insoluble N. View Large Growing Phase Average daily gain during the first 98 d in the feedlot was increased (P = 0.04; 13%) by the use of growth promotants but not (P = 0.73) by the addition of a protein supplement (Table 3). Dry matter intake, whether expressed in kilograms (DM/d) or on a percent of BW basis, was not affected by management treatment. The use of growth promotants resulted in a 16.7% improvement (P = 0.02) in G:F compared with feeding the silage only or silage plus soybean meal diets. There was no interaction (P = 0.46) between growth promotants and protein supplements. Management treatment GS + LCON [the addition of a moderate amount of soybean meal (4% DM basis) to the silage diet] was included in the trial for comparison with the use of growth promotants in silage-fed cattle (GS/GP). This comparison was conducted to determine if the addition of a protein supplement in a “natural” beef production system could compensate for the withdrawal of hormones and ionophores. In the present trial, the addition of soybean meal (4 % DM basis) to the silage diets did not affect (P = 0.20) ADG. Feeding 4% (DM basis) soybean meal (GS + LCON) increased (P = 0.03) DMI (% BW basis) and decreased G:F (P = 0.01) vs. cattle fed silage and administered growth promotants (GS/GP). Table 3. Animal performance overall and during growing (d 0 to 98) and finishing phases (d 99 to slaughter) of the experiment Management regimen P value1 Item GS2 GS/GP3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs. GS/GP Growing phase ADG, kg 1.03 1.16 1.05 1.05 1.19 0.07 0.04 0.73 0.96 0.20 DMI, kg 6.49 6.66 7.38 7.31 6.89 0.35 0.71 0.13 0.39 0.14 DMI, % BW 2.05 2.00 2.30 2.28 2.08 0.10 0.18 0.10 0.39 0.03 G:F 0.16 0.18 0.14 0.14 0.17 0.01 0.02 0.24 0.46 0.01 Finishing phase ADG, kg 0.74 1.18 1.07 1.13 1.44 0.09 <0.01 <0.01 0.44 0.35 DMI, kg 7.87 8.26 9.42 8.77 9.20 0.46 0.35 0.04 0.97 0.07 DMI, % BW 1.92 1.82 2.18 2.08 2.01 0.10 0.41 0.08 0.89 0.01 G:F 0.09 0.15 0.11 0.13 0.16 0.01 <0.01 <0.01 0.23 0.01 Overall ADG, kg 0.85 1.17 1.06 1.08 1.31 0.06 <0.01 <0.01 0.42 0.17 DMI, kg 7.32 7.50 8.41 8.12 8.05 0.33 0.86 0.04 0.69 0.05 DMI, % BW 2.02 1.89 2.22 2.20 2.02 0.08 0.06 0.07 0.77 <0.01 G:F 0.12 0.16 0.13 0.13 0.16 0.01 <0.01 0.18 0.46 0.01 Management regimen P value1 Item GS2 GS/GP3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs. GS/GP Growing phase ADG, kg 1.03 1.16 1.05 1.05 1.19 0.07 0.04 0.73 0.96 0.20 DMI, kg 6.49 6.66 7.38 7.31 6.89 0.35 0.71 0.13 0.39 0.14 DMI, % BW 2.05 2.00 2.30 2.28 2.08 0.10 0.18 0.10 0.39 0.03 G:F 0.16 0.18 0.14 0.14 0.17 0.01 0.02 0.24 0.46 0.01 Finishing phase ADG, kg 0.74 1.18 1.07 1.13 1.44 0.09 <0.01 <0.01 0.44 0.35 DMI, kg 7.87 8.26 9.42 8.77 9.20 0.46 0.35 0.04 0.97 0.07 DMI, % BW 1.92 1.82 2.18 2.08 2.01 0.10 0.41 0.08 0.89 0.01 G:F 0.09 0.15 0.11 0.13 0.16 0.01 <0.01 <0.01 0.23 0.01 Overall ADG, kg 0.85 1.17 1.06 1.08 1.31 0.06 <0.01 <0.01 0.42 0.17 DMI, kg 7.32 7.50 8.41 8.12 8.05 0.33 0.86 0.04 0.69 0.05 DMI, % BW 2.02 1.89 2.22 2.20 2.02 0.08 0.06 0.07 0.77 <0.01 G:F 0.12 0.16 0.13 0.13 0.16 0.01 <0.01 0.18 0.46 0.01 1 Probability values corresponding to the hypothesis of no effect of growth promotants (GS, GS + HCON vs. GS/GP, GS/GP + HCON), concentrates (GS, GS/GP vs. GS + HCON, GS/GP + HCON), or their interaction (GS, GS/GP + HCON vs. GS/GP, GS + HCON). The last contrast tested the hypothesis that the effect of low concentrates did not differ from the effect of feeding silage to cattle administered growth promotants (GS + LCON vs. GS/GP). 2 GS = Grass silage only. 3 GP = Growth promotants included feeding of Rumensin (Elanco Division, Eli Lilly Canada, Inc., Guelph, ON) and implanting with Revalor G (Hoechst-Roussel Agri-Vet, Somerville, NJ) in the growing phase and Revalor S (Hoechst-Roussel Agri-Vet) in the finishing phase. 4 LCON = low levels of supplementary concentrates fed. In the growing phase, LCON was the addition of 4% soybean meal to the diet, whereas in the finishing phase, LCON was the addition of 40% rolled barley to the diet. 5 HCON = high levels of supplementary concentrates fed. In the growing phase, HCON was the addition of 8% soybean meal to the diet, whereas in the finishing phase, HCON was the addition of 70% rolled barley to the diet. View Large Table 3. Animal performance overall and during growing (d 0 to 98) and finishing phases (d 99 to slaughter) of the experiment Management regimen P value1 Item GS2 GS/GP3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs. GS/GP Growing phase ADG, kg 1.03 1.16 1.05 1.05 1.19 0.07 0.04 0.73 0.96 0.20 DMI, kg 6.49 6.66 7.38 7.31 6.89 0.35 0.71 0.13 0.39 0.14 DMI, % BW 2.05 2.00 2.30 2.28 2.08 0.10 0.18 0.10 0.39 0.03 G:F 0.16 0.18 0.14 0.14 0.17 0.01 0.02 0.24 0.46 0.01 Finishing phase ADG, kg 0.74 1.18 1.07 1.13 1.44 0.09 <0.01 <0.01 0.44 0.35 DMI, kg 7.87 8.26 9.42 8.77 9.20 0.46 0.35 0.04 0.97 0.07 DMI, % BW 1.92 1.82 2.18 2.08 2.01 0.10 0.41 0.08 0.89 0.01 G:F 0.09 0.15 0.11 0.13 0.16 0.01 <0.01 <0.01 0.23 0.01 Overall ADG, kg 0.85 1.17 1.06 1.08 1.31 0.06 <0.01 <0.01 0.42 0.17 DMI, kg 7.32 7.50 8.41 8.12 8.05 0.33 0.86 0.04 0.69 0.05 DMI, % BW 2.02 1.89 2.22 2.20 2.02 0.08 0.06 0.07 0.77 <0.01 G:F 0.12 0.16 0.13 0.13 0.16 0.01 <0.01 0.18 0.46 0.01 Management regimen P value1 Item GS2 GS/GP3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs. GS/GP Growing phase ADG, kg 1.03 1.16 1.05 1.05 1.19 0.07 0.04 0.73 0.96 0.20 DMI, kg 6.49 6.66 7.38 7.31 6.89 0.35 0.71 0.13 0.39 0.14 DMI, % BW 2.05 2.00 2.30 2.28 2.08 0.10 0.18 0.10 0.39 0.03 G:F 0.16 0.18 0.14 0.14 0.17 0.01 0.02 0.24 0.46 0.01 Finishing phase ADG, kg 0.74 1.18 1.07 1.13 1.44 0.09 <0.01 <0.01 0.44 0.35 DMI, kg 7.87 8.26 9.42 8.77 9.20 0.46 0.35 0.04 0.97 0.07 DMI, % BW 1.92 1.82 2.18 2.08 2.01 0.10 0.41 0.08 0.89 0.01 G:F 0.09 0.15 0.11 0.13 0.16 0.01 <0.01 <0.01 0.23 0.01 Overall ADG, kg 0.85 1.17 1.06 1.08 1.31 0.06 <0.01 <0.01 0.42 0.17 DMI, kg 7.32 7.50 8.41 8.12 8.05 0.33 0.86 0.04 0.69 0.05 DMI, % BW 2.02 1.89 2.22 2.20 2.02 0.08 0.06 0.07 0.77 <0.01 G:F 0.12 0.16 0.13 0.13 0.16 0.01 <0.01 0.18 0.46 0.01 1 Probability values corresponding to the hypothesis of no effect of growth promotants (GS, GS + HCON vs. GS/GP, GS/GP + HCON), concentrates (GS, GS/GP vs. GS + HCON, GS/GP + HCON), or their interaction (GS, GS/GP + HCON vs. GS/GP, GS + HCON). The last contrast tested the hypothesis that the effect of low concentrates did not differ from the effect of feeding silage to cattle administered growth promotants (GS + LCON vs. GS/GP). 2 GS = Grass silage only. 3 GP = Growth promotants included feeding of Rumensin (Elanco Division, Eli Lilly Canada, Inc., Guelph, ON) and implanting with Revalor G (Hoechst-Roussel Agri-Vet, Somerville, NJ) in the growing phase and Revalor S (Hoechst-Roussel Agri-Vet) in the finishing phase. 4 LCON = low levels of supplementary concentrates fed. In the growing phase, LCON was the addition of 4% soybean meal to the diet, whereas in the finishing phase, LCON was the addition of 40% rolled barley to the diet. 5 HCON = high levels of supplementary concentrates fed. In the growing phase, HCON was the addition of 8% soybean meal to the diet, whereas in the finishing phase, HCON was the addition of 70% rolled barley to the diet. View Large Despite their high CP content, grass silages are considered a poor substrate for rumen microbial protein synthesis and are low in ruminally undegradable protein (Titgemeyer and Loëst, 2001). Veira et al. (1994, 1995) demonstrated that the addition of soybean meal (8% DM basis) to a grass silage-based diet resulted in greater ADG for implanted growing cattle. However, the ADG response varied considerably from one study (+14%; Veira et al., 1994) to the other (+57%; Veira et al., 1995). Previously, Veira et al. (1990) had observed that the addition of a smaller amount of soybean meal (4% DM basis) increased ADG (+14%) of implanted steers fed medium- to high-quality grass silage, although this difference was not statistically significant. Those authors hypothesized that soybean meal increased postruminal amino acid absorption by stimulating microbial protein synthesis in the rumen. In the current study, soybean meal had little effect on ADG (+2%), suggesting that ruminal fermentation was not improved and that ADG was limited by other dietary factors such as energy (Titgemeyer and Loëst, 2001). Growth promotants increased ADG by 13% and reduced DMI by 6%, thereby improving feed efficiency by 14%. The magnitude of the response reported in the current study was greater than that reported in the NRC (1996), similar to the data reported by Ainslie et al. (1992b) using Holstein steers fed alfalfa silage but lower than reported by Lowman et al. (1991) using Charolais cross yearling steers fed grass silage. There was no interaction between the use of growth promotants and protein supplementation as reported by Lowman et al. (1991). However, Gill et al. (1987) reported a significantly greater response to protein supplementation in calves fed silage diets and implanted with an estrogenic growth promotant. Finishing Phase Average daily gain during the finishing phase (Table 3) increased (P < 0.01) with the use of growth promotants or the addition of barley (70% DM basis). However, DMI was affected (P = 0.04) only by the addition of barley (70% DM basis) to the diet. Consequently, use of growth promotants or barley supplementation improved (P = 0.01) feed efficiency. There was no obvious explanation for the poor performance of steers fed grass silage because silage quality (Table 2) was very similar during the course of the whole study and the housing of cattle in a controlled environment sheltered them from sudden changes in environmental conditions. However, it is well documented that as animals reach maturity the energy-to-protein requirement for growth increases (NRC, 1996). This would have rendered the silage diet energy deficient for the heavier steers (Titgemeyer and Loëst, 2001). The fact that steers receiving growth promotants (hormones and ionophores) maintained their performance is likely the result of the combined effects of anabolic agents (trenbolone + estradiol) on the composition of the gain and of the improved capture of feed energy during fermentation in the rumen associated with the use of ionophores (NRC, 1996). The addition of an intermediate level of barley (40% DM basis) was not sufficient to compensate for the abandonment of growth promotants. Results from the finishing phase are very similar to those previously reported by Veira et al. (1983) with implanted steers fed grass silage supplemented with 41 and 57% (DM basis) of high moisture barley between weaning and slaughter but greater than those reported by Petit and Flipot (1992) and Petit et al. (1994) with steers receiving no growth promotants. In both instances, authors reported no interaction between protein supplementation during the growing phase and steer performance during the finishing phase. Overall Performance Overall, ADG for animals treated with growth promotants or fed supplemented diets (soybean meal and barley) increased (P < 0.01) 28 and 18%, respectively, vs. steers reared as “natural” beef (i.e., finished on grass silage alone and not treated with growth promotants). Because DMI (kg of DM/d) increased (P = 0.04) with the addition of supplements to the diet, G:F was only improved (P < 0.01) by the use of growth promotants. There was no interaction between growth promotants and supplements, indicating that growth promotants are effective with forage-based and grain-based diets. Moderate amounts of supplements were provided to the grass silage diet in both the growing (4% soybean meal) and finishing phase (40% rolled barley) in an attempt to improve performance without resorting to the use of growth promotants. Although this approach did not affect (P = 0.17) ADG, the feeding of 4% soybean meal followed by 40% rolled barley increased (P < 0.01) DMI (% BW), resulting in a decrease (P = 0.01) in G:F vs. steers fed silage and treated with growth promotants. This suggests that replacing growth promotants with moderate amounts of grain would not be an efficient proposition on a growth performance basis. Carcass Quality The most common effects of implants have been to increase BW and HCW (Foutz et al., 1997; Rumsey et al., 1999; Roeber et al., 2000) lean yield, and LM area (Rumsey et al., 1992; Kerth et al., 1995; Roeber et al., 2000). These effects have usually been studied in beef cattle receiving ionophores in their feed (Rumsey et al., 1992; Gerken et al., 1995; Woodward and Fernández, 1999). However, no interaction between implants and ionophores was detected in past studies (Perry et al., 1983; Hardt et al., 1995). Hence, it was unlikely that the combination of the 2 growth promotants would have a synergistic effect on carcass measurements in the current study. With the exception of BW and HCW that were increased (P < 0.01) by the use of growth promotants, carcass characteristics were unaffected by the use of a combined implant (trenbolone acetate + estrogen) and an ionophore in cattle either finished exclusively on grass silage or grain forage diets (Table 4). The effects of implants on BW and HCW were consistent with most of the literature and reflected the greater ADG recorded in the growing and finishing phases of this study. Similar to Gerken et al. (1995) and Samber et al. (1996), implants did not affect LM area in the current study. Past studies (Solis et al., 1989; Woodward and Fernández, 1999) reported up to 4 times greater rates of fat deposition in nonimplanted steers compared with implanted steers consuming the same diets. Those authors suggested that the lower fat deposition occurred because the nonimplanted steers required longer time to reach their targeted market BW. In the current study, a difference in days on feed between implanted and nonimplanted steers (+13 d for nonimplanted steers) was also found, but because our objective was to slaughter animals at a constant end point (8 mm backfat), no difference in fat deposition due to growth promotants was recorded. Anabolic growth promotants may compromise carcass quality grades because of reduced marbling and increased proportion of dark cutters (Herschler et al., 1995; Scanga et al., 1998; Roeber et al., 2000). However, neither marbling (P = 0.52) nor lean color (P = 0.67) were affected by implants in this study. Therefore, it is not surprising that quality grade was not affected (P = 0.27) by their use in the current study. Although this agrees with Kerth et al. (1995), it is in contrast with Roeber et al. (2000) who reported greater percentages of greater quality grade (Prime plus Choice) carcasses in nonimplanted vs. implanted steers. It could be argued that the application of 6 d aging before grading might have reduced and thus masked the difference in color and marbling score between treatments. Aging produces a discoloration of fresh meat from red to brown (Faustmann and Cassens, 1990; María et al., 2003) and may have inflated apparent marbling and color scores. However, because most of the carcasses marketed in Quebec are aged for the same time, the appearance of beef observed in this study should correspond to that displayed in the meat counter. Fat color was not altered (P = 0.91) by implant treatment in the present experiment, agreeing with Rumsey et al. (1999). Table 4. Carcass characteristics of steers treated with growth promotants and fed dietary supplements Management regimen P value1 Item GS2 GS/G3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs GS/GP BW, kg 451.2 490.2 474.7 466.9 513.4 8.1 <0.01 <0.01 0.57 0.09 HCW, kg 265.4 286.1 279.2 279.3 306.9 5.4 <0.01 <0.01 0.44 0.26 Dressing yield, % 58.8 58.4 58.7 59.9 59.8 0.6 0.75 0.04 0.78 0.69 Backfat at ¾ position, mm 7.5 7.3 8.8 10.8 8.9 1.0 0.30 0.02 0.40 0.28 Grade fat, mm 6.0 5.6 7.5 9.7 7.9 1.1 0.31 0.01 0.50 0.23 LM area, cm2 70.9 71.4 68.3 70.2 77.4 3.3 0.23 0.41 0.31 0.48 Lean yield, % 59.8 59.4 58.0 57.0 59.1 1.2 0.47 0.17 0.28 0.39 Marbling score6 4.9 4.7 5.4 5.6 5.4 0.3 0.52 0.03 0.87 0.12 Lean color7 3.8 4.0 4.1 4.0 4.0 0.3 0.67 0.67 0.81 0.68 Fat color8 4.0 4.0 4.0 3.9 3.9 0.1 0.91 0.11 0.91 1.00 Quality grade9 1.6 1.2 2.1 2.4 2.1 0.3 0.27 <0.01 0.79 0.03 Management regimen P value1 Item GS2 GS/G3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs GS/GP BW, kg 451.2 490.2 474.7 466.9 513.4 8.1 <0.01 <0.01 0.57 0.09 HCW, kg 265.4 286.1 279.2 279.3 306.9 5.4 <0.01 <0.01 0.44 0.26 Dressing yield, % 58.8 58.4 58.7 59.9 59.8 0.6 0.75 0.04 0.78 0.69 Backfat at ¾ position, mm 7.5 7.3 8.8 10.8 8.9 1.0 0.30 0.02 0.40 0.28 Grade fat, mm 6.0 5.6 7.5 9.7 7.9 1.1 0.31 0.01 0.50 0.23 LM area, cm2 70.9 71.4 68.3 70.2 77.4 3.3 0.23 0.41 0.31 0.48 Lean yield, % 59.8 59.4 58.0 57.0 59.1 1.2 0.47 0.17 0.28 0.39 Marbling score6 4.9 4.7 5.4 5.6 5.4 0.3 0.52 0.03 0.87 0.12 Lean color7 3.8 4.0 4.1 4.0 4.0 0.3 0.67 0.67 0.81 0.68 Fat color8 4.0 4.0 4.0 3.9 3.9 0.1 0.91 0.11 0.91 1.00 Quality grade9 1.6 1.2 2.1 2.4 2.1 0.3 0.27 <0.01 0.79 0.03 1 Probability corresponding to the hypothesis of no effect of growth promotants (GP), concentrates (CON), or their interaction. The last contrast tested the hypothesis that the effect of low concentrates (LCON) did not differ from the effect of feeding silage to cattle administered GP. 2 GS = Grass silage only. 3 GP = Growth promotants include feeding of Rumensin (Elanco Division, Eli Lilly Canada Inc., Guelph, ON) and implanting with Revalor G (Hoechst-Roussel Agri-Vet, Somerville, NJ) in the growing phase and Revalor S (Hoechst-Roussel Agri-Vet) in the finishing phase. 4 LCON = low levels of supplementary concentrates fed. In the growing phase, LCON was the addition of 4% soybean meal to the diet whereas in the finishing phase, LCON was the addition of 40% rolled barley to the diet. 5 HCON = high levels of supplementary concentrates fed. In the growing phase, HCON was the addition of 8% soybean meal to the diet whereas in the finishing phase, HCON was the addition of 70% rolled barley to the diet. 6 According to pictorial standards (from 1 = devoid to 10 = abundant marbling; USDA, 1989). 7 Subjective score for color of the lean using a 5-point scale (from 1 = very dark to 5 = very light cherry). 8 Subjective score for fat color using a 5-point scale (from 1 = lemon yellow to 5 = white). 9 AAA = 4; AA = 3; A = 2; B = 1. View Large Table 4. Carcass characteristics of steers treated with growth promotants and fed dietary supplements Management regimen P value1 Item GS2 GS/G3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs GS/GP BW, kg 451.2 490.2 474.7 466.9 513.4 8.1 <0.01 <0.01 0.57 0.09 HCW, kg 265.4 286.1 279.2 279.3 306.9 5.4 <0.01 <0.01 0.44 0.26 Dressing yield, % 58.8 58.4 58.7 59.9 59.8 0.6 0.75 0.04 0.78 0.69 Backfat at ¾ position, mm 7.5 7.3 8.8 10.8 8.9 1.0 0.30 0.02 0.40 0.28 Grade fat, mm 6.0 5.6 7.5 9.7 7.9 1.1 0.31 0.01 0.50 0.23 LM area, cm2 70.9 71.4 68.3 70.2 77.4 3.3 0.23 0.41 0.31 0.48 Lean yield, % 59.8 59.4 58.0 57.0 59.1 1.2 0.47 0.17 0.28 0.39 Marbling score6 4.9 4.7 5.4 5.6 5.4 0.3 0.52 0.03 0.87 0.12 Lean color7 3.8 4.0 4.1 4.0 4.0 0.3 0.67 0.67 0.81 0.68 Fat color8 4.0 4.0 4.0 3.9 3.9 0.1 0.91 0.11 0.91 1.00 Quality grade9 1.6 1.2 2.1 2.4 2.1 0.3 0.27 <0.01 0.79 0.03 Management regimen P value1 Item GS2 GS/G3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs GS/GP BW, kg 451.2 490.2 474.7 466.9 513.4 8.1 <0.01 <0.01 0.57 0.09 HCW, kg 265.4 286.1 279.2 279.3 306.9 5.4 <0.01 <0.01 0.44 0.26 Dressing yield, % 58.8 58.4 58.7 59.9 59.8 0.6 0.75 0.04 0.78 0.69 Backfat at ¾ position, mm 7.5 7.3 8.8 10.8 8.9 1.0 0.30 0.02 0.40 0.28 Grade fat, mm 6.0 5.6 7.5 9.7 7.9 1.1 0.31 0.01 0.50 0.23 LM area, cm2 70.9 71.4 68.3 70.2 77.4 3.3 0.23 0.41 0.31 0.48 Lean yield, % 59.8 59.4 58.0 57.0 59.1 1.2 0.47 0.17 0.28 0.39 Marbling score6 4.9 4.7 5.4 5.6 5.4 0.3 0.52 0.03 0.87 0.12 Lean color7 3.8 4.0 4.1 4.0 4.0 0.3 0.67 0.67 0.81 0.68 Fat color8 4.0 4.0 4.0 3.9 3.9 0.1 0.91 0.11 0.91 1.00 Quality grade9 1.6 1.2 2.1 2.4 2.1 0.3 0.27 <0.01 0.79 0.03 1 Probability corresponding to the hypothesis of no effect of growth promotants (GP), concentrates (CON), or their interaction. The last contrast tested the hypothesis that the effect of low concentrates (LCON) did not differ from the effect of feeding silage to cattle administered GP. 2 GS = Grass silage only. 3 GP = Growth promotants include feeding of Rumensin (Elanco Division, Eli Lilly Canada Inc., Guelph, ON) and implanting with Revalor G (Hoechst-Roussel Agri-Vet, Somerville, NJ) in the growing phase and Revalor S (Hoechst-Roussel Agri-Vet) in the finishing phase. 4 LCON = low levels of supplementary concentrates fed. In the growing phase, LCON was the addition of 4% soybean meal to the diet whereas in the finishing phase, LCON was the addition of 40% rolled barley to the diet. 5 HCON = high levels of supplementary concentrates fed. In the growing phase, HCON was the addition of 8% soybean meal to the diet whereas in the finishing phase, HCON was the addition of 70% rolled barley to the diet. 6 According to pictorial standards (from 1 = devoid to 10 = abundant marbling; USDA, 1989). 7 Subjective score for color of the lean using a 5-point scale (from 1 = very dark to 5 = very light cherry). 8 Subjective score for fat color using a 5-point scale (from 1 = lemon yellow to 5 = white). 9 AAA = 4; AA = 3; A = 2; B = 1. View Large Research has indicated variable results when comparing carcass measurements from forage- vs. grain-finished cattle (Veira et al., 1983; Allen et al., 1996; Mandell et al., 1998). According to Allen et al. (1996), this lack of consistency is particularly evident when high-quality forages are grazed. Steers fed barley grain in the current study had heavier (P < 0.01) BW and HCW than steers fed grass silage, which was in agreement with Hammes et al. (1964) and Mandell et al. (1998). These results are consistent with Steen and Kilpatrick (2000) with steers fed increasing proportions of concentrate (from 0 to 360 g/kg of rolled barley) in grass-silage-based diets and Zaman et al. (2002) with steers fed intercropped barley/ryegrass compared with cattle fed barley silage. However, the latter 2 studies found similar carcass dressing proportions between feeding treatments. The feeding of a 70% barley diet in the current study increased dressing yield (P = 0.04) and average backfat thickness at the grading site (P < 0.01). This was unexpected as ultrasound backfat measurements taken before shipping were not different (data not shown). The reason for the lack of correlation between ultrasound and grader backfat remains unexplained. There was no effect of barley supplementation on LM area (P = 0.41) or lean yield (P = 0.17) in the current study, which was in agreement with Steen and Kilpatrick (2000) and Zaman et al. (2002). Many studies reported lower marbling in forage-finished compared with grain-finished cattle (Bidner et al., 1981; Rumsey et al., 1987; Schaake et al., 1993), whereas other studies failed to find a difference between the 2 feeding treatments (Mandell et al., 1998; Steen and Kilpatrick, 2000; Zaman et al., 2002). In the current study, supplementation with barley grain (70% DM basis) increased marbling score (P = 0.03), and the greater marbling score resulted in better quality grade (P < 0.01). Although Smith (1990) reported darker muscle color and yellow fat color in forage-finished steers compared with grain-finished cattle, lean (P = 0.67) and fat (P = 0.11) color were similar between diets in the current study. Mandell et al. (1997, 1998) did not observe differences in lean and fat color ratings in carcasses from steers finished with grain or forage. Cost of Production The economic impact of targeting a “natural” beef niche market was evaluated with differences in the costs of feed and yardage (Table 5). As with measures of carcass quality, no interactions were observed. The use of growth promotants did not affect the number of days on feed (P = 0.49) or feed costs per animal (P = 0.15) but decreased (P = 0.02) feed costs per kilogram of gain by 16%, an improvement similar to the one reported by Sawyer et al. (2003). Yardage costs per animal or per day increased (P < 0.01) with the use of hormones and ionophores. However, yardage costs per kilogram of gain decreased (P < 0.01) by 13.4% when animals received growth promotants confirming the results of others (Fernández and Woodward, 1999; Sawyer et al., 2003). Moreover, in the present trial, the use of growth promotants did not have a negative effect on carcass grading, further supporting the economics of using these products. The abandonment of hormones and ionophores associated with the production of “natural” beef would need to be compensated by a market premium of more than 15% if producers were to maintain their profit margin per kilogram of gain. Table 5. Cost of production and cost of gain as affected by use of growth promotants or concentrate supplementation Management regimen P value1 Item GS2 GS/GP3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs GS/GP Initial BW, kg 266 273 269 272 273 5.1 0.21 0.37 0.25 0.30 D 98 BW, kg 367 387 373 374 390 9.5 0.03 0.56 0.77 0.22 Final BW, kg 461 513 487 473 530 9.5 <0.01 0.06 0.74 0.02 ADG, kg 195 239 218 202 257 9.4 <0.01 0.14 0.48 0.06 Days on feed, d 234 210 208 186 197 10.4 0.49 <0.01 0.09 0.89 Cost/steer,6 $ Feed7 168.41 175.94 238.15 227.59 250.02 11.16 0.15 <0.01 0.47 <0.01 Yardage8 106.96 113.16 103.12 99.84 110.84 1.33 <0.01 <0.01 0.07 <0.01 Yardage/d 0.46 0.55 0.50 0.54 0.57 0.02 <0.01 0.01 0.11 0.06 Total9 275.39 288.91 341.46 327.43 360.87 12.06 0.04 <0.01 0.38 <0.01 Cost/kg of gain,9 $ Feed 0.86 0.73 1.10 1.14 1.00 0.06 0.02 <0.01 0.88 <0.01 Yardage 0.55 0.47 0.48 0.50 0.44 0.02 <0.01 0.03 0.79 0.76 Total 1.42 1.20 1.58 1.65 1.44 0.07 <0.01 <0.01 0.99 <0.01 Management regimen P value1 Item GS2 GS/GP3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs GS/GP Initial BW, kg 266 273 269 272 273 5.1 0.21 0.37 0.25 0.30 D 98 BW, kg 367 387 373 374 390 9.5 0.03 0.56 0.77 0.22 Final BW, kg 461 513 487 473 530 9.5 <0.01 0.06 0.74 0.02 ADG, kg 195 239 218 202 257 9.4 <0.01 0.14 0.48 0.06 Days on feed, d 234 210 208 186 197 10.4 0.49 <0.01 0.09 0.89 Cost/steer,6 $ Feed7 168.41 175.94 238.15 227.59 250.02 11.16 0.15 <0.01 0.47 <0.01 Yardage8 106.96 113.16 103.12 99.84 110.84 1.33 <0.01 <0.01 0.07 <0.01 Yardage/d 0.46 0.55 0.50 0.54 0.57 0.02 <0.01 0.01 0.11 0.06 Total9 275.39 288.91 341.46 327.43 360.87 12.06 0.04 <0.01 0.38 <0.01 Cost/kg of gain,9 $ Feed 0.86 0.73 1.10 1.14 1.00 0.06 0.02 <0.01 0.88 <0.01 Yardage 0.55 0.47 0.48 0.50 0.44 0.02 <0.01 0.03 0.79 0.76 Total 1.42 1.20 1.58 1.65 1.44 0.07 <0.01 <0.01 0.99 <0.01 1 Probability corresponding to the hypothesis of no effect of growth promotants (GP), concentrates (CON), or their interaction. The last contrast tested the hypothesis that the effect of low concentrates (LCON) did not differ from the effect of feeding silage to cattle administered GP. P > 0.05 indicates no significant (NS) difference. 2 GS = Grass silage only. 3 GP = Growth promotants included feeding of Rumensin (Elanco Division, Eli Lilly Canada Inc., Guelph, ON) and implanting with Revalor G (Hoechst-Roussel Agri-Vet, Somerville, NJ) in the growing phase and Revalor S (Hoechst-Roussel Agri-Vet) in the finishing phase. 4 LCON = low levels of supplementary concentrates fed. In the growing phase, LCON was the addition of 4% soybean meal to the diet, whereas in the finishing phase, LCON was the addition of 40% rolled barley to the diet. 5 HCON = high levels of supplementary concentrates fed. In the growing phase, HCON was the addition of 8% soybean meal to the diet, whereas in the finishing phase, HCON was the addition of 70% rolled barley to the diet. 6 All costs were calculated individually for the period of time each steer was on feed. 7 Feed cost = price paid for the feed × amount consumed during each phase. 8 Yardage = costs for labor + equipment + bedding + veterinary expenses + interest. 9 Total cost of gain includes feed and yardage costs. 10 Cost of gain = cost/total BW gained during the trial (final − initial weight). View Large Table 5. Cost of production and cost of gain as affected by use of growth promotants or concentrate supplementation Management regimen P value1 Item GS2 GS/GP3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs GS/GP Initial BW, kg 266 273 269 272 273 5.1 0.21 0.37 0.25 0.30 D 98 BW, kg 367 387 373 374 390 9.5 0.03 0.56 0.77 0.22 Final BW, kg 461 513 487 473 530 9.5 <0.01 0.06 0.74 0.02 ADG, kg 195 239 218 202 257 9.4 <0.01 0.14 0.48 0.06 Days on feed, d 234 210 208 186 197 10.4 0.49 <0.01 0.09 0.89 Cost/steer,6 $ Feed7 168.41 175.94 238.15 227.59 250.02 11.16 0.15 <0.01 0.47 <0.01 Yardage8 106.96 113.16 103.12 99.84 110.84 1.33 <0.01 <0.01 0.07 <0.01 Yardage/d 0.46 0.55 0.50 0.54 0.57 0.02 <0.01 0.01 0.11 0.06 Total9 275.39 288.91 341.46 327.43 360.87 12.06 0.04 <0.01 0.38 <0.01 Cost/kg of gain,9 $ Feed 0.86 0.73 1.10 1.14 1.00 0.06 0.02 <0.01 0.88 <0.01 Yardage 0.55 0.47 0.48 0.50 0.44 0.02 <0.01 0.03 0.79 0.76 Total 1.42 1.20 1.58 1.65 1.44 0.07 <0.01 <0.01 0.99 <0.01 Management regimen P value1 Item GS2 GS/GP3 GS + LCON4 GS + HCON5 GS/GP + HCON SEM GP CON GP × CON GS + LCON vs GS/GP Initial BW, kg 266 273 269 272 273 5.1 0.21 0.37 0.25 0.30 D 98 BW, kg 367 387 373 374 390 9.5 0.03 0.56 0.77 0.22 Final BW, kg 461 513 487 473 530 9.5 <0.01 0.06 0.74 0.02 ADG, kg 195 239 218 202 257 9.4 <0.01 0.14 0.48 0.06 Days on feed, d 234 210 208 186 197 10.4 0.49 <0.01 0.09 0.89 Cost/steer,6 $ Feed7 168.41 175.94 238.15 227.59 250.02 11.16 0.15 <0.01 0.47 <0.01 Yardage8 106.96 113.16 103.12 99.84 110.84 1.33 <0.01 <0.01 0.07 <0.01 Yardage/d 0.46 0.55 0.50 0.54 0.57 0.02 <0.01 0.01 0.11 0.06 Total9 275.39 288.91 341.46 327.43 360.87 12.06 0.04 <0.01 0.38 <0.01 Cost/kg of gain,9 $ Feed 0.86 0.73 1.10 1.14 1.00 0.06 0.02 <0.01 0.88 <0.01 Yardage 0.55 0.47 0.48 0.50 0.44 0.02 <0.01 0.03 0.79 0.76 Total 1.42 1.20 1.58 1.65 1.44 0.07 <0.01 <0.01 0.99 <0.01 1 Probability corresponding to the hypothesis of no effect of growth promotants (GP), concentrates (CON), or their interaction. The last contrast tested the hypothesis that the effect of low concentrates (LCON) did not differ from the effect of feeding silage to cattle administered GP. P > 0.05 indicates no significant (NS) difference. 2 GS = Grass silage only. 3 GP = Growth promotants included feeding of Rumensin (Elanco Division, Eli Lilly Canada Inc., Guelph, ON) and implanting with Revalor G (Hoechst-Roussel Agri-Vet, Somerville, NJ) in the growing phase and Revalor S (Hoechst-Roussel Agri-Vet) in the finishing phase. 4 LCON = low levels of supplementary concentrates fed. In the growing phase, LCON was the addition of 4% soybean meal to the diet, whereas in the finishing phase, LCON was the addition of 40% rolled barley to the diet. 5 HCON = high levels of supplementary concentrates fed. In the growing phase, HCON was the addition of 8% soybean meal to the diet, whereas in the finishing phase, HCON was the addition of 70% rolled barley to the diet. 6 All costs were calculated individually for the period of time each steer was on feed. 7 Feed cost = price paid for the feed × amount consumed during each phase. 8 Yardage = costs for labor + equipment + bedding + veterinary expenses + interest. 9 Total cost of gain includes feed and yardage costs. 10 Cost of gain = cost/total BW gained during the trial (final − initial weight). View Large Conversely, the use of concentrates (8% soybean meal and 70% barley) in the diet increased (P < 0.01) feed costs per animal (+41%) and per kilogram of gain (+34%) despite a 30 d decrease (P < 0.01) in the number of days on feed for concentrate vs. forage-fed steers, implying that forage-fed beef is more economical to produce. However, this conclusion is dependent on the relative cost of forages compared with concentrates and on the effect of the shorter feeding period (minus 30 d) on the fixed cost structure of the farm. In this experiment, the cost of grass silage was estimated at $100/t of DM whereas the cost of purchased rolled barley was $197/t of DM for a ratio of 1.97 between grain and forage. This was considerably larger than the values previously used in comparisons between forage and grain diets (Loerch, 1996; Ainslie et al., 1992a). Hence, if the cost of silage was increased by 20% ($120/t of DM) and the cost of barley was reduced by the same proportion ($158/t of DM), then feed costs per kilogram gain in the finishing phase were virtually the same. It must also be noted that supplements had a positive effect on HCW, carcass quality, and grading (Table 4). These factors would have a considerable influence on the income associated with both production systems. IMPLICATIONS With early maturing cattle, the use of growth promotants produced heavier carcasses and had no effect on other carcass measurements regardless of the diet provided (forage- vs. grain-based diet). Thus, producers who choose to raise steers in finishing systems with no implants or ionophores would get the same price per kilogram of carcass but a lower income per steer as those using management systems with these growth promotants. Also, producers must consider the longer time required to raise cattle to the targeted slaughter weight when excluding growth promotants from their production systems. This delay would have an impact on fixed costs and farm structure. Finally, although this study suggests that forage-fed, nonimplanted beef would cost less (31%) than implanted grain-fed beef, the reduction in HCW (16%) and quality grade (31%) would result in a lower income for the producer unless consumers would be willing to pay a premium for this product. 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