|dc.description.abstract||Experiment 1 consisted of the evaluation of behavioral characteristics of growing steers in response to implant, feeding duration, diurnal rhythm and dietary roughage via monitoring of activity and rumination time. Charolais × Angus steers (n = 80) were randomized to harvest (0, 42, 84, 126, 168, 210, 252, 294, 336 or 378 DOF) and implant treatment (REV: Revalor-XS; on d-0 and d-190 or CON: no implant). Activity and rumination were objectively monitored via accelerometers attached to the left ear. Steers consumed 3 rations throughout the study: starter (38.5% roughage), intermediate (23% roughage), and finishing (8.5% roughage). Data was logged in 2-h increments from 77 steers across 361 d and analyzed using mixed models for repeated measures of activity and rumination. Rumination and activity varied (P < 0.01) within 24-h, exhibiting bimodal patterns; rumination peaked at 0600 and 1400 h and troughed at 1000 and 1800 h. Activity peaked at 0800 and 1800 h and troughed at 0400, 1200-1400, and 2200 h. Steers administered REV ruminated less (364 vs 380 min/d; P = 0.04) than CON, however, 24-h activity was similar (P = 0.29) between treatments. Treatment × roughage interactions (P < 0.01) occurred for rumination and activity. Rumination tended to differ (P = 0.06) between CON consuming 38.5% and 23% roughage, however, CON steers ruminated (P < 0.01) more than REV when consuming 8.5% roughage. Implanted and non-implanted steers ruminated less (P < 0.01) as roughage inclusion decreased from 38.5% and 23% to 8.5% (457 and 439 vs 317 min/d) in the finishing ration. Activity was highest for steers consuming 38.5% roughage and was similar (P > 0.05) among treatments, however, activity decreased (P < 0.01) upon transition to 23 and 8.5% roughage. Activity peaks and troughs can be attributed to processing days and weather events. Implanted steers consuming 8.5% roughage were more active (342 vs. 337 and 333 min/d; P < 0.01) than steers of both treatments consuming 23% roughage. In conclusion, rumination and activity are responsive to hour of day, dietary roughage and growth-promoting implants.
Experiment 2 was conducted to investigate the development of non-carcass components of implanted or non-implanted Charolais × Angus steers across various marketing endpoints. Growth promoting implants containing trenbolone acetate (TBA) and estradiol-17β (E2) are administered to improve rate of gain and feed efficiency of beef cattle. Non-carcass components are by-products of the beef industry that are of metabolic, economic and societal importance. A serial-harvest was conducted to investigate growth of non-carcass components of implanted or non-implanted Charolais × Angus steers. Steers (n = 80) were paired and applied to a 2 x 10 factorial treatment structure in a balanced incomplete block design. Steers were randomly appointed to harvest date (0, 42, 84, 126, 168, 210, 252, 294, 336 or 378 days on feed; DOF) and implant treatment; REV received a Revalor-XS (200mg TBA/40mg E2) on d0 and d190, whereas CON received no implant. Pair was block, steer was experimental unit and data were analyzed using mixed models. Four REV/CON pairs were harvested upon each feeding endpoint. Non-carcass components were removed and weighed; gastrointestinal tracts (GIT) were disassembled, weighed, cleaned, and re-weighed. Empty body weight (EBW), and hot carcass weight (HCW) were 6% greater (P < 0.01) in REV steers vs. CON. No treatment effects (P ≥ 0.12) were observed for fill or dressed carcass yield (DY), however, EBW, HCW and DY increased (P ≤ 0.01) and percentage fill decreased as an effect of DOF. Absolute fill weight did not change across DOF (P ≥ 0.82). Implanted steers had greater (P ≤ 0.05) absolute mass of blood, head, hide, oxtail, liver, spleen, bladder, heart, reticulum, omasum, stomach, small intestine, intestines, GIT, total splanchnic tissue and total offal. Implanted steers also had smaller (P ≤ 0.05) absolute mass of thymus glands and kidney-pelvic-heart fat (KPH) than non-implanted steers. Absolute mass of the spinal cord, small intestine and intestines varied across DOF but did not exhibit linear or quadratic growth, whereas all other tissue weights increased (P ≤ 0.05) or tended to increase (P ≤ 0.06) with DOF. The brain, limbs, thymus, abomasum, KPH and total internal fat (TIF) of REV steers weighed proportionately less (P ≤ 0.03) and the reticulum weighed proportionately more (P = 0.03) than those of CON steers. Proportionate weight of the bladder, gallbladder and spleen was similar for all DOF, whereas all other variables differed (P ≤ 0.04) across DOF. Observed results suggest that TBA + E2 implants increase body and carcass weights and alter many non-carcass components, while reducing excess internal fat accumulation.
Improved efficiency associated with TBA + E2 implants has been attributed to a shift in nutrient deposition away from fat deposits often trimmed from the final product, toward the development of lean muscle. Though a decrease in waste fat will improve carcass cutability, a concurrent reduction in intramuscular fat and carcass quality is often observed in implanted animals marketed prior to achieving target composition. A third experiment was designed to evaluate the development of traits contributing to carcass yield and quality in response to implant and days on feed (DOF) in a 2 × 10 factorial study. Charolais × Angus steers (n = 80) were paired for similarity using genetic markers and projected endpoint composition. Pairs were randomized to 1 of 10 harvest dates corresponding to 0, 42, 84, 126, 168, 210, 252, 294, 336 or 378 DOF. Individuals within pair were then randomly assigned to 1 of 2 implant treatments, in which REV steers received a Revalor-XS (200mg trenbolone acetate/40mg estradiol; 4 uncoated and 6 coated pellets) implant on d 0 and d 190, while CON steers represented a non-hormone treated (NHTC) marketing strategy and received no implant throughout the feeding period. Upon each feeding endpoint, 8 steers (4-REV/CON pairs) were harvested and the shrunk body weight (SBW), weight of kidney, pelvic and heart fat (KPH), and hot carcass weight (HCW) were obtained. Carcasses were chilled for 48 h and graded according to USDA quality and yield grade standards. All variables were analyzed using mixed models with implant treatment and DOF as fixed effects and pair as random. While no TRT × DOF interactions (P > 0.05) were observed in yield grade variables, a TRT × DOF interaction occurred (P < 0.01) for skeletal and overall maturity. Implanted steers had a heavier SBW (7%; P < 0.01) and HCW (6%; P < 0.01), and larger (6%; P < 0.01) LM area than non-implanted counterparts. While REV carcasses had 17% less (P < 0.01) KPH than CON carcasses, no treatment effects (P = 0.26) were observed in marbling, suggesting sustained marbling quality throughout the 378-d feeding period. Marbling and 12th rib fat depth increased linearly (P < 0.01) across DOF; SBW, HCW, dressed yield, LM area, KPH, USDA yield grade, and lean maturity increased whereas LM area:HCW decreased quadratically (P < 0.06) with additional DOF. These data support a shift in nutrient deposition from waste-fat accumulation to lean tissue development in response to slow-release TBA + E2 implants compared to NHTC. Additionally, implanted steers exhibited advanced skeletal maturity, however no concurrent compromise in marbling was observed throughout the 378-d feeding period.||