A comparison of the productive performance of single and twin born Merino ewes

Abstract

A comparison has been made of the productive performance of448 single and 466 twin born ewes. The data was obtained over eight years from five autumn mated, single character selection flocks maintained at Trangie Agricultural Research Station. The following highly significant, mean percentage differences were recorded in favour of singles :-fold score, 16.5 ; weaning weight, 12.8 ; 18 month body weight, 3.9 ; greasy fleece weight, 2.9. A 4.3 per cent difference in classing score and a 2.2 per cent difference in clean fleece weight approached the 5 per cent level of significance (P<0.1). Weaning weight analysis revealed a significant interaction between year and type of birth caused by the relatively improved performance of twins in years which favoured lamb growth. An analysis of the components of clean fleece weight showed that the lowered wool production of twins was associated with a decrease in the total number of wool fibres per sheep, caused by reductions in skin area and in the proportion of secondary fibres. Twins and singles did not differ in fibre density, diameter or length. The analysis of fertility (total number of lambs mothered at the first two matings) showed a significant interaction between type of birth and jock. Single born Weight Minus ewes were more fertile, whereas in the other four flocks the difference favoured twins. Without the Weaning Weight Minus flock, twins showed a highly significant advantage of 16.9 per cent in percentage lambs mothered. This difference could be wholly accounted for by higher incidence of multiple births.