RESPONSE OF CASTRATED MALE SHEEP TO ESTROGENIC AND ANDROGENIC COMPOUNDS IMPLANTED ALONE OR IN COMBINATION

Forty-eight Greyface wether lambs, aged about 6 months and weighing 32 kg on average were used. They were allocated to be treated, by subcut aneous implantation in the upper surface of the ear flap, with the nat urally occurring steroids oestradiol-17 beta (O), testosterone (T) or the synthetically produced androgen trenbolone acetate (TA). Treatment groups were as follows: sham-implanted controls (C); 50 mg O (slow re lease formulation) (O); 40 mg TA (compressed pellets) (TA); 50 mg T (c ompressed pellets) (T); 15 mg O + 40 mg TA (TAO); 15 mg O + 50 mg T (T O). Combined implants were placed in close proximity under the skin of the same ear. The lambs were offered, to appetite, a good quality die t containing per kg dry matter (DM) an estimated 12.0 MJ metabolizable energy and 150 g crude protein. Comparisons were made for the main ef fects of O and the androgens T and TA. Main effects due to O were incr eased DM intake, live-weight gain (LWG) empty body weight (EBW), chill ed carcass weight (CCW), carcass crude protein (CP) deposition, plasma insulin concentrations and tent length with reductions recorded for t he proportion but not weight of fat in the carcass, plasma urea and th yroxine concentrations. Treatment with androgens did not, on average, influence LWG or other indices of growth performance or carcass compos ition other than to produce significant increases in carcass phosphor us deposition and reduction in the depth of thorax. Significant increa ses in the weight of penile tissue and reductions in tent length were recorded. There was evidence for a greater androgenic effect on penile tissue and anti-oestrogenic effect (on tent length) of TA compared wi th T at the concentrations used. TA also reduced the weight of the thy mus gland, an effect reversed in the presence of O. Analysis of plasma taken from the vein contralateral to the site of implantation showed that O concentrations were I educed in the presence of TA and T, and t hat O had no effect on the concentrations of androgens measured. Conce ntrations of T and 17 beta-hydroxy-trenbolone in blood were of a simil ar order, which for T is typical of post-pubertal entire male sheep. T he results suggest that O treatment Tons effective in promoting growth and carcass CP deposition which ions not increased by T or TA, despit e the presence of these androgens at biologically active concentration s in blood. This effect appears to differ from the additive effects fr equently obtained castrated male cattle.