Effect of Three Different Initial Implant Programs on BeefxDairy Steer Feedlot Performance and Carcass Characteristics

Abstract Increased prevalence of beef×dairy cattle at finishing has left producers searching for ways to optimize performance though growth-promoting technologies. The objective of this study was to evaluate timing and dosage of trenbolone acetate (TBA) administration on live and carcass outcomes of beef×dairy steers. Beef×dairy steers (n = 6,895; initial body weight = 156±5.2kg) were allotted into 30 pens, with pen as the experimental unit. Pens were assigned one of three implant treatments: 1) Revalor-IS (IS) at d0, IS at d80, and Revalor-XS (XS) at d160 (IS/IS/XS); 2) Ralgro at d0, IS at d80, and XS at d160 (Ral/IS/XS); 3) Encore at d0 and XS at d160 (Enc/XS). Steers were blocked by arrival date, each pen was terminally sorted after d250, and shipped at 329 ± 25d. For live outcomes, effects of implant treatment and block were evaluated. For carcass outcomes, effects of implant treatment, terminal sort group, interaction of treatment×sort, and block were evaluated. IS/IS/XS and Ral/IS/XS were heavier (P< 0.001) than Enc/XS steers at d160. Final body weight was numerically increased for IS/IS/XS, but not statistically different (P=0.15). Bullers decreased from IS/IS/XS to Ral/IS/XS to Enc/XS (P< 0.001). Dry matter consumption increased (P< 0.01) from Enc/XS to IS/IS/XS. Average daily gain and feed efficiency were similar (P≥0.11). Hot carcass weight numerically increased (P=0.30) for IS/IS/XS compared to Enc/XS steers. Dressed yield, heavy carcasses, and 12th rib fat thickness were similar (P≥0.16). Marbling score differed (P=0.04), and Enc/XS graded a greater proportion of USDA Prime and fewer USDA Select carcasses than IS/IS/XS (P< 0.05). Fewer Enc/XS and Ral/IS/XS tended (P=0.07) to be yield grade (YG) 3, with numerically more YG 1 and 2 carcasses than IS/IS/XS. While delaying administration of aggressive implants may improve quality grade and decrease bullers, few performance differences were observed as a result of initial implant.