Resorcylic acid lactone as an anabolic agent in cattle

This paper discusses the use of resorcylic acid lactone as an anabolic agent in cattle. When given to finishing steers it increases daily gain by 10–18% and final carcass weight by 6–10 kg. When given to finishing steers in conjunction with trenbolone acetate, there is an additive response in terms of growth rate and carcass weight. The final carcass weights were 310±2.1, 319±2.0, 316±2.0 and 328±2.0 for unimplanted steers, or steers implanted with resorcylic acid lactone or trenbolone acetate or a combination of both compounds respectively. Responses in finishing steers in spring at pasture were similar to responses obtained in winter. In male calves, average liveweights at the end of a 134-day experimental period were 123, 142 and 140 kg (SE ± 5.4 kg) respectively for control calves or calves given resorcylic acid lactone or a combination of resorcylic acid lactone and trenbolone acetate. After a further 134 days grazing together these calves weighed 271, 294 and 297 kg (SE ± 7.9 kg) respectively, indicating that the extra gain was retained once the implants ceased to be effective. No significant effect on daily gain or carcass weight of heifers was obtained in our trials with resorcylic acid lactone. Results from feed efficiency trial indicated resorcylic acid lactone significantly increased feed efficiency. Therefore, resorcylic acid is an effective growth promoter in male castrate cattle.