The β3-adrenergic agonist (BRL35135A) improves feed efficiency and decreases visceral but not subcutaneous fat in lambs

There is evidence that an atypical adrenoreceptor subtype is involved in mediating some of the physiological effects of catecholamines, particularly in some adipose tissue sites. Therefore, a study was conducted to determine the effect of the β3-agonist BRL35135A on growth performance and body composition in ruminant lambs. Twenty-two second cross wether lambs (32.5 ± 0.7 kg) were individually-housed in pens and randomly allocated on the basis of stratified live weights to two treatments (n = 11 per treatment). The control group were offered barley (20%) and lucerne chaff (80%) ad libitum and the treated group were given the BRL35135A (1 mg/30 kg live weight) with the feed. Feed refusals were recorded daily and lambs weighed weekly. After 42 days all lambs were slaughtered commercially and carcass, visceral organ and fat depots recorded. Chilled carcasses were scanned by dual-energy X-ray absorptiometry to measure body composition. Dietary β3-agonist treatment had no effect on average daily gain, final live weight or carcass weight but reduced residual feed intake (0.41 vs −0.41, P = 0.061). There were no effects of dietary β3-agonist treatment on carcass chemical composition but β3-agonist treatment increased the weight of the feet (0.89 vs 0.94 kg, P < 0.05) and the skin (4.22 vs 4.56 kg, P < 0.05). Dietary β3-agonist treatment decreased the weight of the omental (0.64 vs 0.51 kg, P < 0.05) and perirenal (0.30 vs 0.23 kg, P < 0.05) fat depots. In conclusion, these data confirm that BRL35135A was active in sheep when given with feed, as indicated by a partitioning of nutrients from visceral fat mass and an improvement in feed efficiency. The effects on adipose tissue were specific to omental and perirenal fat as there was no change in carcass fat and these data are consistent with β3-receptors being the predominant β-receptor subtype in internal fat tissues.