Lifetime growth and carcass composition of heifers and steers non-implanted or sequentially implanted with anabolic agents

Abstract

ABSTRACTSixty-four (48 female and 16 male) spring-born Hereford × Friesian calves were used to examine the effects of sex type, heifer slaughter age and implantation with anabolic agents on growth and carcass composition. Non-implanted and implanted heifers were slaughtered after 491, 612 and 731 days and non-implanted and implanted steers (castrated on day 81) were slaughtered after 731 days. Implantation was with 36 mg resorcylic acid lactone (RAL) on days 81 and 171 and RAL plus 300 mg trenbolone acetate on days 395, 491, 583 and 658.Carcass weights of non-implanted and implanted heifers slaughtered at 491, 612 and 731 days were 189 and 206, 218 and 235 and 290 and 326 (s.e.d. 10·1) kg respectively. Carcass lean, bone and fat weights and fat proportion increased with increasing slaughter age but proportions of lean and bone decreased.There was no difference between heifers and steers in growth rate to 395 days but from 395 to 731 days the steers grew faster than the heifers. Non-implanted and implanted steer carcass weights at 731 days were 297 and 355 (s.e.d. 9·5) kg respectively. Steer carcasses had higher lean and bone proportions and a lower fat proportion than heifer carcasses. Implanted animals had heavier carcasses than non-implanted animals and all of the extra carcass weight consisted of lean and bone. The results indicate that non-implanted and implanted heifers and steers had similar lean proportions when the heifers were 31 and 70 kg carcass weight respectively lighter than the steers.