EFFECT OF NATURALLY-OCCURRING AND SYNTHETIC ANDROGENS ON GROWTH, BODY-COMPOSITION AND MUSCLE GLUCOCORTICOID RECEPTORS IN WETHER LAMBS

Twenty-five Border Leicester male X Blackface female wether lambs aged about 4 months and weighing on average 28.5 kg were allocated to be t reated with the naturally occurring steroid testosterone or trenbolone acetate or nandrolone phenylpropionate which are steroids synthetical ly produced. Treatment groups were as follows: untreated controls (C); 50 mg testosterone (T); 50 mg trenbolone acetate (TA); 50 mg testoste rone + 50 mg trenbolone acetate (TTA) or 50 mg nandrolone phenylpropio nate (N). Implants were given at 100 and again at 63 days before slaug hter. The lambs were offered to appetite a good quality diet containin g, per kg dry matter, an estimated 11.0 MJ metabolizable energy and 18 5 g crude protein. Comparisons were made for the main effects of T and TA and also interactions between T and TA. Effects due to N were asse ssed statistically against untreated controls. Treatment with T, on av erage, increased live-weight gain (LWG), empty body weight (EBW) and r educed backfat thickness and the weight (g/kg EBW) of perirenal and re troperitoneal fat. Main effects due to TA were increases in killing-ou t ratio and depth of the gigot joint and reductions in backfat thickne ss. Treatment with N increased the empty body weight and (g/kg) carcas s ash. Non-significant (P > 0.05) trends were suggested for increases in carcass crude protein due to T and TA treatments. T and TA but not N treatments exhibited marked androgenic activity in increasing the we ight (mg/kg EBW) of the accessary vesicular gland. TA and N, but not T , reduced the weight (g/kg EBW) of the thymus gland. The maximum bindi ng capacity of post-mortem skeletal muscle (m. gluteus) for (H-3)-dexa methasone was reduced by TA but increased by T and N. These results su ggest differences in the binding capacity of corticosteroid receptors which may be related to differences in the effects of T and TA on prot ein metabolism in skeletal muscle.