Growth, carcass characteristics and androgen concentrations of gonad-altered ram lambs

Abstract

The study was designed to determine the effect of multiple types of gonadal alteration on circulating androgen concentrations, the rate of body weight gain, and carcass characteristics, when lambs were slaughtered at approximately 41 kg versus 49 kg of shorn-shrunk body weight. Seventy-four lambs, 2 months old were placed in the experiment and continued until lambs reached the planned body weight in each group. Ram lambs were assigned at random across the two slaughter weight groups to be treated in six groups as follows: Group I, intact rams; Group II, rams to be castrated unilaterally; Group III, rams to be castrated unilaterally plus removal of the tail of the epididymis of the remaining testis; Group IV, bilateral short scrotum rams to simulate cryptorchidism; Group V, unilateral short scrotum rams, and the other testis removed; Group VI, rams bilaterally castrated (wethers); plus Group VII, ewe lambs. Compensatory hypertrophy of the scrotal testis occurred in the groups with unilateral castration, and the short scrotum ram testes were smaller. Circulating plasma testosterone and androstenedione concentrations were not markedly affected by any gonadal treatment, except that they remained at baseline levels in the bilaterally castrated rams, comparable to the ewes. Daily weight gain was less in these latter two groups ( P<0.05), but was not different from the other groups. At both slaughter weights, wethers and ewes had less lean, more fat, less bone, and a lower yield of trimmed or untrimmed retail cuts ( P<0.05). They also recorded a higher carcass quality grade. These studies indicate that all gonadal alterations which maintain androgen secretion produce beneficial effects, similar to intact rams on growth and most carcass characteristics. Slaughtering younger animals at lower weights produced leaner carcasses.