Effect of zeranol implants in ram and wether lambs on performance traits, carcass characteristics, and subprimal cut yields and distribution

In two separate 2 X 2 factorial arrangements, 69 male, crossbred lambs were allotted randomly to the following treatments: 1) nonimplanted (NI) rams, 2) implanted (I) rams, 3) NI wethers, and 4) I wethers. In Trial 1, 36 lambs were allotted to treatment groups at birth (n = 9) and I lambs were implanted with 12 mg of zeranol between 1 and 3 d of age and again at weaning (average age of 62 d). Lambs were slaughtered at three time-constant end points of 78, 93, and 107 d on feed postweaning (average age of 155 d). Rams grew faster postweaning, were more efficient in their feed conversion, were heavier at slaughter, and had lower numerical yield grades than did wethers (P < .05). Implanted lambs tended (P = .08) to grow faster and were (P < .05) more efficient in their feed conversion than NI lambs. Rams produced heavier (P < .05) trimmed subprimal shoulders, loins, and legs and had (P < .05) a higher percentage of their carcass weight in the subprimal shoulder than did wethers. During Trial 2, NI rams (n = 8), I rams (n = 8), NI wethers (n = 8), and I wethers (n = 9) were allotted to treatment groups, and I lambs were implanted at average ages of 14, 55, and 98 d. After weaning, lambs were weighed every 14 d and were slaughtered 7 d after reaching a minimum weight of 50 kg (average age of 148 d). Rams grew faster postweaning and required fewer days to reach 50 kg (132 vs 151 d) than did wethers (P < .05). No differences (P > .05) occurred due to treatments for, yield grades or subprimal weights and percentages. In both trials, I rams had (P < .05) smaller scrotal circumferences and lighter testicular weights than did NI rams. Implanting with zeranol beginning near birth may improve postweaning performance in ram and wether lambs but has minimal effects on carcass yield and quality and subprimal yield and distribution. Although rams have greater performance, cutability, subprimal cut weights, and percentage of subprimal shoulder than do wethers (Trial 1), differences in carcass and subprimal yields can be minimized by slaughtering rams at a constant weight and at a younger age (Trial 2).