Effects of breed, season of lambing and fecundity level on production per ewe and per hectare

Production per ewe and output per hectare were measured from the ewes of self-replacing, wool sheep flocks, stocked at 500 kg liveweight/ha on mixed annual-perennial pasture species in a temperate zone with 700 mm annual winter rainfall, near Hamilton in Victoria. Ewes of 2 breeds, a small body-sized, fine wool (20 pm) Merino and a larger body-sized, medium wool (23 pm) comeback, were compared at 2 lambing seasons (May or August) and at 2 levels of fecundity (natural or enhanced) from 1982 to 1985. Supplements were fed to prevent nutritional stress. Comeback ewes were about 10% heavier (P<0.01), produced 0.8 kg more (P<0.001) wool and reared more (P<0.01) lambs (0.93 v. 0.77) than Merinos, however, output per hectare was similar for both breeds. Ewes lambing in August required less (P<0.05) feed supplement than those lambing in May to produce similar wool and lamb output per hectare. Treatments to induce extra ovulations increased lambing rate in both ewe breeds. The mean change was from 1.06 to 1.23 lambs/ewe (P<0.01), but due to the high mortality of twins, lamb weaning rate and weight per hectare were not increased. When combined with the results from other studies, we conclude that the mean flock wool weight/ha is closely correlated to the mean ewe mating liveweight/ha across a range of wool sheep which differ in size and wool production because of either genotype or environment.