Abstract

Growth rates, carcass composition and management problems of "short scrotum" rams (made by elevating the testes to a position against the abdominal wall using rubber rings), wethers and entire male lambs were compared on a hill country property in northern Hawkes Bay. Of 3 groups of 65 Perendale lambs selected randomly at docking at about 4 weeks of age, 1 group was left entire, 1 was made short scrotum and the other was castrated. The lambs were weaned at about 10 weeks of age, separated from the main flock at about 14 weeks of age and thereafter kept as 1 flock until slaughter at 9 months of age. They were weighted every 6 weeks from 14 weeks of age. After the removal of 6 lambs from each group for detailed investigation at Massey University, the top 50 lambs from each group were slaughtered and their carcass characteristics recorded. Short scrotum rams showed management advantages over normal ram lambs. They were easier to handle, and avoided the works hygiene problem of dirty genitalia. Short scrotum rams had an overall live-weight advantage of 3kg over wether lambs. This was found not to be due to fat deposition, as short scrotum rams showed a significantly lower GR of 3.3mm, compared with normal rams (4.6mm) and wethers (6.2mm), as predicted by regression for lambs of 32kg live weight. There was no significant difference in carcass weight or dressing percentage between lambs of this live weight, although more normal rams and short scrotum rams fell into heavier grades than did the wether lambs. In detailed investigations on 6 lambs from each group, no differences were found in muscle:bone ratio or fat distribution between the groups. Short scrotum rams had very low fertility; 50 of 56 had no epididymal sperm reserves and 6 had extremely low sperm production. Most sperm from short scrotum rams were abnormal. Short scrotum rams had significantly lighter testes and epididymides than normal rams. Short scrotum rams had plasma LH levels intermediate to normal rams and wethers. Differences between entire and short scrotum rams in testosterone levels varied inconsistently

JL, Owens, B Kyle, and PF Fennessy

Proceedings of the New Zealand Society of Animal Production, Volume 46, , 41-44, 1986