The performance of short scrotum and wether lambs born in winter or spring and run at pasture in northern Tasmania

Abstract

Summary. The growth of short scrotum and wether lambs was studied in 3 experiments over 2 years, at the Elliott Research Station in northern Tasmania. Short scrotum lambs born in winter grew significantly (P<0.05) faster than wethers from birth to slaughter at 137 days of age. For spring born, short scrotum lambs, the growth advantage was less because of the quality and quantity of pasture available during summer and autumn. Wether lambs were fatter than short scrotum lambs in all experiments, with the slope of the relationship between GR and carcass weight being 0.57 ¦ 0.02 I! 0.42 ¦ 0.01 mmkg (experiment 1); 1.13 ¦ 0.1 1 v. 0.68 ¦ 0.09 mm/kg (experiment 2); and 0.91 ¦ 0.16 v. 0.63 ¦ 0.08 mm/kg (experiment 3) respectively. As carcass weight increased, the difference in carcass fatness increased. There was a shift in the distribution of carcasses according to fat score, with more wether carcasses being allocated high fat scores. Testes weight in the short scrotum lambs showed considerable variation within and between experiments and in all cases the testes were located in a subcutaneous position. There was a poor relationship between testes weight and growth rate. The level of testes development in a proportion of animals indicated that the animals could be fertile.