AN APPRAISAL OF SELECTION IN THE ROMNELET SHEEP

Abstract

The amounts of selection for birth weight, weaning weight, post-weaning gain up to about 1 year of age and yearling clean fleece weight in the development of the Romnelet breed of sheep are reported.The selection differentials for weaning weight only were statistically significant (P < 0.05) for both sexes. Analyses of regression of mean differential on time showed an upward trend in the differentials for birth weight and weaning weight, but there was no evidence of significant yearly trend in the differentials for post-weaning traits. Trends in selection pressure were consistent with the reported genetic trends in performance after the initial decline in performance from F1 to F2.Weaning weight received more attention in selection than any other trait studied, and the most genetic improvement was made in this trait. The large reduction in numbers of animals available for selection from birth to one year of age, due mainly to heavy culling of lambs at weaning, brought about a reduction in selection intensity from 22 per cent to 10 per cent for post-weaning gain and from 42.5 to 22 per cent for clean fleece weight.