Comparison of a modified cryptorchid treatment and castration: effect on growth, wool production, posthitis, testosterone production and development of masculine characteristics

摘要

Male lambs born to Merino, Polwarth and Merino x Polwarth ewes were used to study a technique for manipulating testicular size. Of these lambs, 82 were castrated at marking (wethers). For the remaining 100 the testicular parenchyma was removed at marking and then, at a subsequent date, the scrotal sac and any large testicles were removed (modified cryptorchids). Cryptorchids were significantly (P<0.05) heavier than wethers throughout the study and produced significantly (P<0.05) heavier fleeces (4.3 ¦ 0.08 v. 4.0 ¦ 0.06 kg). Bin class, as an indicator of wool quality, was not significantly different between the 2 groups. At all times of the year, cryptorchids had a significantly lower prevalence (P<0.001) and severity of posthitis. Posthitis increased in spring and decreased in summer. There was significantly (P<0.001) more horn development in the cryptorchids, and Merino-sired animals had more horn development than those sired by Polwarth rams. The basal level of testosterone in the wethers was 0.08 ¦ 0.07 ng/mL averaged over 3 successive blood samples, compared to the cryptorchids at 0.95 ¦ 0.16 ng/mL with an asymmetric distribution. The rank correlation between average testosterone levels and testicle score was significant (P<0.05) with a coefficient of 0.54. The rank correlations between testosterone levels and fleeceweight, liveweight or horn score were not significant (P>0.05).