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The effects of zilpaterol hydrochloride (ZH) on blood metabolites and fatty acid profiles of plasma and adipose tissue were evaluated in crossbred finishing steers (n = 18, BW 639 ± 12.69 kg) that were stratified by BW and randomly assigned, within strata (block), to receive 0 (control) or 8.33 mg/kg diet DM ZH. Cattle were fed once daily ad libitum in individual feeding pens (9 pens/treatment). Zilpaterol hydrochloride was fed for 23 d and withdrawn 3 d before harvest. Blood samples and measures of BW were taken on d 0, 7, 14, and 21. Concentrations of β-hydroxybutyrate (BHB), glucose, and lactate were determined from whole blood. Nonesterified fatty acids, urea nitrogen (PUN), glucose, lactate, and long-chain fatty acid (LCFA) concentrations were analyzed from plasma. Postharvest, adipose tissue samples (approximately 20 g) from subcutaneous fat covering the lumbar vertebrae were collected after 48 h of refrigeration and analyzed for LCFA profiles. Feeding ZH decreased DMI by 8% (P = 0.03) but did not affect BW gain or efficiency (P = 0.83 and P = 0.56, respectively). Addition of ZH resulted in greater HCW, dressing percentage, and LM area (P = 0.02, P = 0.08, and P = 0.07, respectively) but did not influence other carcass traits (P > 0.10). A ZH × d interaction was observed for PUN and whole-blood glucose concentrations (P = 0.06), in which concentrations decreased in cattle receiving ZH. Nonesterified fatty acids, BHB, plasma glucose, whole-blood, and plasma lactate concentrations were unaffected by ZH (P > 0.10). Zilpaterol hydrochloride increased plasma concentrations of elaidic (P = 0.03), vaccenic (P = 0.006), and docosapentaenoic acids (P = 0.08), but LCFA concentrations of adipose tissue were unaffected (P > 0.10), suggesting no preferential oxidation of specific fatty acids. In conclusion, ZH supplementation decreased PUN concentration possibly due to decreased muscle catabolism, but components of blood related to lipid oxidation were unaffected. [ABSTRACT FROM AUTHOR]

Crossbred yearling steers (n = 80; 406 ± 2.7 kg of BW) were used to evaluate the effects of S concentration in dried distillers grains with solubles (DDGS) on growth performance, carcass characteristics, and ruminal concentrations of CH4 and H2S in finishing steers fed diets based on steam-flaked corn (SFC) or dry-rolled corn (DRC) and containing 30% DDGS (DM basis) with moderate S (0.42% S, MS) or high S (0.65% S, HS). Treatments consisted of SFC diets containing MS (SFC-MS), SFC diets containing HS (SFC-HS), DRC diets containing MS (DRC-MS), or DRC diets containing HS (DRC-HS). High S was achieved by adding H2SO4 to DDGS. Ruminal gas samples were analyzed for concentrations of H2S and CH4. Steers were fed once daily in quantities that resulted in traces of residual feed in the bunk the following day for 140 d. No interactions (P ≥ 0.15) between dietary S concentration and grain processing were observed with respect to growth performance or carcass characteristics. Steers fed HS diets had 8.9% less DMI (P < 0.001) and 12.9% less ADG (P = 0.006) than steers fed diets with MS, but S concentration had no effect on G:F (P = 0.25). Cattle fed HS yielded 4.3% lighter HCW (P = 0.006) and had 16.2% less KPH (P = 0.009) than steers fed MS. Steers fed HS had decreased (P = 0.04) yield grades compared with steers fed MS. No differences were observed among treatments with respect to dressing percentage, liver abscesses, 12th-rib fat thickness, LM area, or USDA quality grades (P = 0.18). Steers fed SFC had less DMI (P < 0.001) than steers fed DRC. Grain processing had no effect (P > 0.05) on G:F or carcass characteristics. Cattle fed HS had greater (P < 0.001) ruminal concentrations of H2S than cattle fed MS. Hydrogen sulfide concentration was inversely related (P ≤ 0.01) to ADG (r = -0.58) and DMI (r = -0.67) in cattle fed SFC, and to DMI (r = -0.40) in cattle fed DRC. Feeding DDGS that are high in dietary S may decrease the DMI of beef steers and compromise the growth performance and carcass characteristics of feedlot cattle. [ABSTRACT FROM AUTHOR]

Yearling steers (n = 2,552; 314 kg of initial BW) were used to evaluate the effects of ractopamine-HCI (RAC) and days on feed on performance, carcass characteristics, and skeletal muscle gene expression in finishing steers. Treatment groups included serial slaughter dates of 150, 171, or 192 d on feed. Within each slaughter date, steers either received RAC (200 mg/steer) daily for the final 28 d or were not fed RAC. All steers were initially implanted with Revalor- IS and were reimplanted with Revalor-S after 75 d on feed. At slaughter, muscle samples from the semimem-branosus were collected for mRNA analysis of the β adrenergic receptors (β-AR). Ractopamine administration increased (P < 0.05) ADG, G:F, and HCW and increased (P = 0.08) LM area. Ractopamine did not affect the dressing percentage, USDA yield grade, or quality grade (P > 0.3). There was no change in overall feed intake across the entire feeding period; however, feed intake was increased during the 28-d period during which the steers were fed RAC (P ⩽ 0.05). Greater days on feed decreased (P < 0.05) AUG, G:F, DM1, and the number of yield grade 1 and 2 carcasses. Also, greater days on feed increased (P < 0.05) HCW, dressing percentage, and the number of prime and choice carcasses, as well as the number of yield grade 4 and 5 carcasses. Increasing days on feed decreased (P < 0.05) the abundance of β1-AR and β2-AR mRNA and increased (P < 0.05) the abundance of β2-AR mRNA in skeletal muscle samples obtained at slaughter. Ractopamine had no effect (P > 0.10) on the abundance of β1-AR or β3-AR mRNA, but tended (P = 0.09) to increase β2-AR mRNA. Additional time-course studies with primary muscle cell cultures revealed that advancing time in culture increased (P < 0.001) β2-AR mRNA but had no effect (P > 0.10) on β1-AR or β3-AR mRNA. We conclude that days on feed and RAC are affecting β-AR mRNA levels, which could, in turn, impact the biological response to RAC feeding in yearling steers. [ABSTRACT FROM AUTHOR]

Previous research has shown that low dosages of capsicum oleoresin positively affected individual behavior of cattle housed in small pens. The objective of this trial was to assess the effect of a product standardized with 20% capsicum oleoresin (XT; XTRACT Caps XL, Pancosma) on behavior of feedlot cattle farmed under typical U.S. commercial conditions during the summer. A total of 28 pens regrouping 3,874 cattle (average BW at start of 426 kg) were paired according to pen type and density for 30 d. Within each pair, pens were assigned to either a control total mixed ration diet with monensin (CT) or the same diet supplemented with 250 mg/animal per day XT (XT). Dry matter intake was recorded daily for each pen. Behavior was recorded per pen, once before the trial and then 3 times during the study by 2 examiners. Panting score, percentage of standing versus laying animals, and number of animals at waterers and feed bunk were collected. Dry matter intake was analyzed using the mixed models procedure of SAS, with day, treatment, and their interaction considered fixed effects. Equality of variances for DMI was assessed using a Fisher F-test. Behavior data were analyzed by a χ² test. Results showed that the treatments did not affect DMI (mean 10.7 kg/animal per day; P = 0.57). However, daily variation of intake tended to be lower in the XT treatment than in the CT group (P < 0.06), suggesting that capsicum induced a more homogeneous DMI. The proportion of animals standing versus lying was not affected by the treatments (P > 0.70) as well as at the waterer and at the feeder (means of 5.81 and 7.82%, respectively; P > 0.20). The proportion of cattle with a panting score greater than 2 was lower in XT than in CT (7.90 vs. 8.10%; P = 0.15); however, the biological relevance of this small difference is difficult to interpret. These findings suggest that capsicum supplementation has the potential to modulate intake variation, and this may limit negative effects of a hot season in feedlot cattle raised under commercial conditions. [ABSTRACT FROM AUTHOR]

Two-thousand sixty English × Continental steer calves (avg. 252 kg) were used in a randomized complete block study to evaluate the effects of ractopamine and DOF on performance and carcass traits. Steers were blocked by arrival time at the research facility. On each arrival d cattle were processed and randomly allotted to 6 pens of 75 to 125 head each. All steers received Revalor-IS (16 mg estradiol-17β (E2) and 80 mg trenbolone acetate (TBA)) upon arrival and were reimplanted with Revalor-S (24 mg E2 and 120 mg TBA) on d 75. Within each block, three pens were randomly selected to receive ractopamine at the rate of 200 mg/hd daily for the final 28 d on feed (RAC) and the remaining three were fed no ractopamine (CON). Within each treatment and block combination, pens were randomly assigned to be fed for either 181, 202, or 223 d. There were 4 reps per treatment × DOF combination for a total of 24 pens. When measured over the entire feeding period, feeding RAC increased ADG 2.7% and increased final weight 6.8 kg. There was an interaction between DOF and treatment for feed conversion (P < 0.10), as RAC improved G:F (P < 0.05) in steers fed 202 d but had no effect on steers fed either 181 or 223 d. Feeding RAC also increased HCW 4.6 kg, increased the percentage of Yield Grade 1 carcasses by 6% units and decreased the percent grading Choice by 8% units (P < 0.05). All other carcass measurements were similar. Additional DOF resulted in linear increases in final wt and DMI and linear decreases in ADG and G:F (P < 0.05). There were no interactions between treatment and DOF for carcass traits. Increasing DOF caused linear increases in dressing percentage, HCW, fat thickness, marbling score, percentage Prime combined with Choice, and Yield Grade (P < 0.05). Increasing DOF decreased performance and increased carcass fatness but increased carcass quality and carcass weight. Feeding RAC improved performance regardless of DOF; however, RAC had a less pronounced effect on growth in this study with calves than has been reported elsewhere using yearling steers. [ABSTRACT FROM AUTHOR]

Yearling steers (n=2,252; avg. 314 kg) were used to evaluate the effects of Optaflexx™ and d on feed on finishing steer performance and carcass characteristics. This study utilized a randomized complete block with a 3×2 factorial arrangement. Treatment groups included serial harvest dates of 150, 171, or 192 d. Within harvest date, steers either received Optaflexx (200 mg/steer daily of ractopamine-HCl) for the final 28 d, or did not receive Optaflexx. All steers were initially implanted with Revalor-IS and were re-implanted with Revalor-S after 75 d on feed. At harvest, muscle samples from the inside round were obtained for analysis of β-adrenergic receptor (AR) mRNA levels. Optaflexx increased daily gains, hot carcass weight, ribeye area, and G:F (P ≤ 0.05). Optaflexx did not affect dressing percent, USDA yield grade, or quality grade (P > 0.3). There was no change in overall feed intake across the entire feeding period; however, feed intake was increased during the 28-d period that steers were fed Optaflexx (P 0.05). As expected, greater d on feed decreased daily gains, overall feed intake, the number of yield grade 1 and 2 carcasses, and G:F (P ≤ 0.05). Also, greater d on feed increased hot carcass weight, dressing percent, and the number of prime and choice carcasses, as well as the number of yield grade 4 and 5 carcasses(P ≤ 0.05). Increasing d on feed decreased the abundance of mRNA for β1-AR and β3-AR, and increased the abundance of β2-AR mRNA (P ≤ 0.05). Optaflexx had no effect on abundance of mRNA for β1-AR, or β3-AR, but it increased the abundance of mRNA for β2-AR (P = 0.09). Further studies with primary muscle cell cultures revealed that advancing time in culture increased the β2-AR mRNA (P ≤ 0.01) but had no effect (P > 0.10) on β1-AR or β3-AR mRNA. These data suggest that d on feed and Optaflexx are affecting βAR mRNA levels which could in turn impact the response to Optaflexx feeding in cattle. [ABSTRACT FROM AUTHOR]

Calf-fed steers (n=2060, 252 kg) were used to determine the effects of Optaflexx and days on feed on finishing performance and carcass characteristics. Treatment consisted of serial harvest dates 181, 202, or 223 d. Within each harvest group, steers received either (200 mg/hd daily of ractopamine-HC1) for the final 28 days, or a control diet consisting of no Optaflexx. All steers were implanted with Revalor-IS (80 mg trenbolone acetate 16 mg estradiol) at processing (d 0), and Revalor-S (120 mg trenbolone acetate and 24 mg estradiol) at 75 days on feed (DOF). At harvest, samples were taken from the inside round for analysis of IGF-I and the β-adrenergic receptors (AR) mRNA abundance. Four samples per treatment per DOF group totaling twenty-four samples were analyzed. Days on feed did not increase abundance of β1-AR (P ≥ 0.38), β2-AR (P ≥ 0.89), β3-AR (P≥0.90) mRNA, but numerically increased the abundance of IGF-I levels (P = 0.21). Addition of Optaflexx had no effect on expression of IGF-I and β-adrenergic receptors (βAR). The data obtained from these calf-fed steers contradict results obtained from older yearling steers in which expression of β2-AR mRNA increased with advanced DOF. Increased understanding of receptor abundance related to DOF and age may explain some response differences in calf-feds vs. yearlings. [ABSTRACT FROM AUTHOR]