Effects of synthetic hormone implants, singularly or in combinations, on performance, carcass traits, and longissimus muscle palatability of Holstein steers

Seventy-two Holstein steers averaging 182 kg were assigned randomly to one of six treatment groups: 1) nonimplanted controls (C); 2) implanted with 36 mg of zeranol (Z); 3) implanted with 20 mg of estradiol benzoate and 200 mg of progesterone (EP); 4) implanted with 140 mg of trenbolone acetate (TBA); 5) implanted with 140 mg of trenbolone acetate plus 20 mg of estradiol benzoate and 200 mg of progesterone (TBA + EP); and 6) implanted with 140 mg of trenbolone acetate plus 36 mg of zeranol (TBA + Z). Each treatment group consisted of three replications of four animals per pen, which were implanted on d 0, 56, 112, and 168. Masculinity and muscling scores were assigned at 24 h preslaughter. Hide removal difficulty was scored by a plant supervisor. Quality and yield grade data were obtained at 24 h postmortem. Longissimus muscle (LM) steaks were removed and cooked for Warner-Bratzler shear (WBS) determinations and sensory panel (SP) evaluations. Over the entire feeding period (249 d), TBA + EP steers had higher (P less than .05) ADG than TBA + Z, TBA, and C steers. All treatments had higher (P less than .05) ADG than C, with the exception of TBA. The only feed efficiency differences were those following the 168-d implant time, when TBA steers were more (P less than .05) efficient than TBA + Z or C steers. The TBA + EP and TBA + Z steers were more (P less than .05) masculine and their hides were more (P less than .05) difficult to remove than those of EP and C steers. Carcass weights of TBA + EP steers were heavier (P less than .05) than those of TBA or C steers. The TBA + EP steers had larger (P less than .05) LM areas than Z, TBA, and C steers. Also, TBA + EP steers tended (P = .07) to have lower numerical yield grades than EP, Z, or C steers. Even though mean marbling scores and quality grades were similar (P greater than .05) among treatment groups, only 50% of TBA + EP carcasses graded low Choice or higher, compared with 100, 75, 82, 90, and 83% for C, TBA, Z, EP, and TBA + Z carcasses, respectively. The only meat palatability differences were that myofibrillar and overall tenderness scores tended to be lower (P = .07) for steaks from EP and TBA + Z than for steaks from Z and C groups.