Hybrid vigour and lamb production. 1. Reproductive performance of the purebred and crossbred matings

Abstract

An experiment was conducted at Cowra Agricultural Research Station, New South Wales, to determine the importance of hybrid vigour to the productivity of crosses between Border Leicester and Merino sheep. In five years, 1963 to 1967, Border Leicester (BL) and Merino (M) rams were paddock-joined to a mixed flock of ewes of both breeds for five weeks in March-April. The results of these purebred and crossbred matings have been compared. Cummulative weekly raddle counts were similar for both purebred mating groups (BL x BL and M x M) and by the end of joining over 95 per cent of ewes in both groups had been raddled. When the mating data for the Border Leicester ewes were examined, Merino rams raddled fewer ewes than did Border Leicester rams. This breed difference between rams was significant for the number of ewes raddled by the end of both the first and second week of joining (P < 0.05) and the difference in favour of the Border Leicester rams was still apparent at the end of joining (97 vs. 86 per cent, not significant). The reproductive performance of the Merino ewes (M x M) was superior to that of the- Border Leicesters (BL x BL), with 1.05 vs. 0.93 lambs born per ewe joined. The Border Leicester flock had higher incidences of both dry ewes (63.7 vs. 79.3 per cent ewes lambing of those joined) and multiple births (1.47 vs. 1.33 lambs born per lambing ewe). Because of the difference in the mating activity of the two Border Leicester ewe flocks (M x BL vs. BL x BL), the most reliable estimates of the relative performance of purebred and crossbred matings were given by the number of lambs born per lambing ewe, and the number of ewes lambing to first service. The crossbred matings were superior for both characteristics, by 4.6 and 5.7 per cent respectively, but neither difference was statistically significant.