Effect of bearing and rearing lambs on Merino wool production

Abstract

Over a 15-year period, the greasy fleece weights of medium-wooled Merino ewes lambing in June in a 625 mm winter rainfall area in south-western Australia were examined in relation to the numbers of lambs born and reared. The ewes were set stocked at 6.7 ewes/ha on annual pasture. During this period selection for increased wool production was undertaken. A generalised linear model was used to assess the effects of bearing and rearing lambs. There was a significant (P<0.05) year x lambing interaction because of a different response over years 1-7 from that over years 8-15. Over years 1-7 when dry ewes cut an average of 4250 g greasy wool, ewes raising single lambs cut 185 g less wool (P<0.001); the few that raised twins cut a similar amount of wool to dry ewes. In years 8-15, wool production of dry ewes increased to an average of 5524 g. Ewes that lambed but lost their lambs cut 386 g less wool, those raising single lambs 652 g less wool, and those raising twins 846 g less wool. Over years 8-15, a second flock in which some ewes lambed twice a year was examined. These ewes received supplementary feed for out of season lambing. Those that raised 2 single lambs in a year cut 1120 g less wool than dry ewes.