The effect of different implant programs on beef × dairy steer feedlot growth performance and carcass characteristics.

The objective of this study was to evaluate potency and timing of trenbolone acetate ( TBA ) administration on live performance and carcass characteristics of beef × dairy steers. A total of 6,895 beef × dairy steers [initial body weight ( BW ) = 157 ± 5.2 kg] were allotted into 30 pens, with pen as the experimental unit. Each pen was randomly assigned one of three implant treatments: 1) Revalor-IS ( IS ) at d 0, IS at d 80, and Revalor-XS ( XS ) at d 160 ( IS/IS/XS ); 2) Ralgro at d 0, IS at d 80, and XS at d 160 ( Ral/IS/XS ); or 3) Encore at d 0 and XS at d 160 ( Enc/XS ). Steers were blocked by arrival date, each pen was terminally sorted in three ways at 257 ± 22 days on feed and harvested at 329 ± 25 days on feed. For live and carcass outcomes, fixed effect of implant treatment and random effect of block was evaluated. Data are reported on a deads and removals out basis. Removals, morbidity, and mortality were similar ( P  ≥ 0.45). Steers administered TBA prior to d 160 were 5.8 kg heavier ( P  = 0.03) than Enc/XS steers at d 160. Final BW was not different ( P  = 0.78). Early administration of a TBA-containing implant resulted in an increased prevalence of bullers [2.40%, 5.18%, 6.86% (for Enc/XS, Ral/IS/XS, and IS/IS/XS) respectively; P  < 0.01]. Dry matter intake ( DMI ) was 2.3% greater ( P  < 0.01) in steers administered Enc/XS compared to IS/IS/XS; however, DMI as a percentage of BW, average daily gain, and feed efficiency were not different ( P  ≥ 0.12). Dressing percentage, hot carcass weight, heavy carcass occurrence, Longissimus muscle area, and 12th rib fat thickness were similar among all steers ( P  ≥ 0.28). Marbling score tended to be greatest for Enc/XS and Ral/IS/XS ( P  = 0.09). Enc/XS graded a greater proportion of USDA Prime and fewer USDA Select carcasses than IS/IS/XS ( P  < 0.05). Enc/XS and Ral/IS/XS tended ( P  = 0.09) to have more USDA Yield Grade ( YG ) 1 carcasses. While delayed administration or decreased total potency of TBA-containing implants may decrease buller incidence and improve Quality Grade, few differences were observed in live or carcass outcomes.
Competing Interests: Authors J. P. Hutcheson and L.-A. J. Walter are employees of Merck Animal Health.
(© The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science.)