INCREASING ANNUAL GROWTH-RATES OF CATTLE BY REDUCING MAINTENANCE ENERGY-REQUIREMENTS

In seasonally dry areas cattle undergo periods of arrested growth because the forage on offer is of poor quality. Annual liveweight gains could be increased and age of turnoff for slaughter reduced if maintenance energy requirements could be lowered during the dry season with no concomitant reduction in forage intake. Strategies to reduce metabolic rate, and so rate of liveweight loss using the anabolic steroid, trenbolone acetate, and the alpha2-agonist, guanfacin, are discussed. Both compounds reduced fasting metabolic rate of steers; an implant of 300 mg trenbolone acetate by about 10% and continuous intravenous infusion of 40 mug/kg liveweight per day guanfacin by about 20%. The effect of other anabolic steroids on energy metabolism is reviewed. Trenbolone treatment of steers fed a low-protein roughage diet reduced voluntary feed intake. The mechanism by which this occurred was established and is discussed, as are studies aimed at determining the mechanism by which trenbolone reduces metabolic rate. Further, it has been established that the guanfacin-induced reduction in metabolic rate which is largely mediated peripherally is an alpha2-adrenergic effect and not some other effect of the drug.