Forty-eight Greyface wether lambs, aged about 6 months and weighing 32 kg on average were used. They were allocated to be treated, by subcutaneous implantation in the upper surface of the ear flap, with the naturally occurring steroids oestradiol-17β (O), testosterone (T) or the synthetically produced androgen trenbolone acetate (TA). Treatment groups were as follows: sham-implanted controls (C); 50 mg O (slow release formulation) (O); 40 mg TA (compressed pellets} (TA); 50 mg T (compressed pellets) (T); 15 mg O + 40 mg TA (TAO); 15 mg O + 50 mg T (TO). Combined implants were placed in close proximity under the skin of the same ear. The lambs were offered, to appetite, a good quality diet containing per kg dry matter (DM) an estimated 12-0 MJ metabolizable energy and 150 g crude protein. Comparisons were made for the main effects of O and the androgens T and TA. Main effects due to O were increased DM intake, live-weight gain (LWG) empty body weight (EBW), chilled carcass iveight (CCW), carcass crude protein (CP) deposition, plasma insulin concentrations and teat length with reductions recorded for the proportion but not weight of fat in the carcass, plasma urea and thyroxine concentrations. Treatment with androgens did not, on average, influence LWG or other indices of growth performance or carcass composition other than to produce significant increases in carcass phosphorus deposition and reduction in the depth of thorax. Significant increases in the iveight of penile tissue and reductions in teat length were recorded. There was evidence for a greater androgenic effect on penile tissue and anti-oestrogenic effect (on teat length) of TA compared with T at the concentrations used. TA also reduced the weight of the thymus gland, an effect reversed in the presence ofO.
Analysis of plasma taken from the vein contralateral to the site of implantation showed that O concentrations were reduced in the presence of TA and T, and that O had no effect on the concentrations of androgens measured. Concentrations ofT and 17 β-hydroxy-trenbolone in blood were of a similar order, which for T is typical of postpubertal entire male sheep.
The results suggest that O treatment was effective in promoting growth and carcass CP deposition which was not increased by T or TA, despite the presence of these androgens at biologically active concentrations in blood. This effect appears to differ from the additive effects frequently obtained for castrated male cattle.