Effects of heifer finishing implants on beef carcass traits and longissimus tenderness

¹ Department of Animal Science, Colorado State University, Fort Collins, CO 80523-1171
² Five Rivers Cattle Feeding, Loveland, CO, 80538

^* To whom correspondence should be addressed. E-mail: J.Daryl.Tatum{at}Colostate.edu.

	Abstract

Effects of finishing implants on heifer carcass characteristics and LM Warner-Bratzler shear force (WBSF) were investigated using commercially fed Continental x British heifers (n=500). Heifers were blocked by initial BW (Block 1: BW 340 kg; Block 2: BW < 340 kg) and assigned randomly to 12 treatments that utilized 0, 1, or 2 finishing implants to deliver cumulative dosages of trenbolone acetate (TBA) and estradiol 17- (E₂) ranging from 0 to 400 mg TBA and 0 to 40 mg E₂ during the finishing period. Heifers in Blocks 1 and 2 were harvested after 135 and 149 d on feed, respectively. At these endpoints, treatment groups did not differ (P > 0.05) in adjusted fat thickness or predicted percent empty body fat. Compared with a non-implanted control, implanting heifers a single time during finishing increased (P = 0.025) HCW by an average of 7.9 kg, without affecting mean marbling score, the percentage of carcasses grading Choice and Prime, or LM WBSF values. Compared with use of 1 implant, use of 2 finishing implants resulted in an additional increase (P = 0.008) in hot carcass weight of 6.0 kg. Re-implanting also increased (P < 0.001) LM area, reduced (P = 0.024) the percentage of KPH fat, and improved (P = 0.004) mean yield grade. However, re-implanted heifers produced a lower (P = 0.044) percentage of carcasses grading Choice and Prime and LM steaks with higher (P < 0.05)WBSF values at all postmortem aging times, compared with heifers that were implanted once. Among heifers receiving 2 implants, mean 14-d LM WBSF increased linearly (P < 0.05) as the cumulative, combined dosage of E₂ plus TBA increased. Heifers implanted with a combination of E₂ plus TBA had larger (P = 0.046) LM areas, lower (P = 0.004) mean marbling scores, and higher LM WBSF values after 3 d (P = 0.001), 7 d (P = 0.001), 14 d (P = 0.003), and 21 d (P = 0.045) of postmortem aging than did heifers implanted with TBA alone. Heifers that received combination implants containing both E₂ and TBA also produced fewer (P = 0.005) carcasses with marbling scores of Modest or higher compared with heifers that received single-ingredient implants containing TBA alone. Implant treatment effects on LM WBSF gradually diminished as length of the postmortem aging period increased. Postmortem aging periods of 14 to 28 d were effective for mitigating detrimental effects of mild or moderately aggressive heifer implant programs on predicted consumer acceptability of LM steaks.

Key Words: Carcass, Grade, Growth Promoters, Heifers, Tenderness