Effects of clenbuterol on growth in underfed cattle

Abstract

This study examined the effects of clenbuterol on the growth of young cattle (160 kg) that were fed a restricted quantity of a low-quality hay to simulate dry-season pasture conditions in the tropics. Twenty Brahman steers were used. Ten control animals lost an average of 0.24 kg/day in the first 17 days, then maintained their liveweight for the remaining 21 days of the experiment. By contrast, 10 clenbuterol-treated animals lost 0.3 kg/day for the first 17 days of the experiment, then continued to lose weight at a steady rate of 0.15 kg/day. In control steers, plasma concentrations of urea-nitrogen decreased over the course of the experiment, and this effect was accelerated by clenbuterol treatment (P < 0.05). There were no marked changes in plasma concentrations of glucose, potassium, or N^t-methylhistidine in response to clenbuterol treatment. Clenbuterol had no effect on β₂ -adrenoceptor density in the longissimus muscle, but there was a marked increase in β₂-adrenoceptors in both groups of cattle over time. Despite their loss of liveweight, the carcasses of clenbuterol-treated cattle were not lighter than controls (74.3 v. 72 kg, respectively) and contained 10% more protein (P < 0.05). This was reflected by a trend towards increased weight of the biceps femoris muscle (9%; P < 0.1). These findings are consistent with clenbuterol causing a drive to deposit muscle protein at the expense of other tissues, even when dietary protein and energy are limited.