Abstract :
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 3-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 dualenergy
X-ray absorptiometry to measure body composition. Dietary 3-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 3-agonist treatment
on carcass chemical composition but 3-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 3-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 3-receptors being the predominant -receptor subtype in internal fat tissues.
