Performance of sheep systems grazing perennial pastures. 2. Wool quality and lamb growth

Abstract

This study evaluated wool quality and lamb production from four management systems with Merino ewes grazing a perennial pasture between 2006 and 2010, using different combinations of lambing time, ram breed and percentage of summer-active pasture species. All systems were stocked at a similar midwinter rate (dry-sheep equivalents per hectare of 8, 10.2, 13, 11.2 and 11.2 in the successive seasons 2006–2010). Liveweight, condition score, C fat and eye muscle depth at weaning of both Merino and crossbred lambs were always higher (P < 0.05) for lambs born in July than those born in September. Similarly, the sale weight of lambs born in July was always higher (P < 0.05) than of lambs born in September, partly because these lambs were usually retained for longer before sale. When lambs were born in September, sheep systems that carried higher numbers of ewes per hectare at the same midwinter stocking rate produced sale weights of lambs similar to those with fewer ewes, except where systems with fewer lambs per hectare enabled lambs to be retained for longer in favourable seasons. A higher percentage of lucerne (Medicago sativa, 40% cf. 20%) increased lamb sale weights only in favourable seasons. Clean fleece weights per ewe and staple strength were similar among systems in most years (2008–2010), although mean fibre diameter was lower (P < 0.05) in both late lambing systems (with 40% and 20% lucerne). The results indicate that choice of lambing time, ram breed and the flexibility to alter lamb sale date with seasonal conditions will have a larger impact on the performance of individuals than number of ewes per hectare where systems are grazed at the same midwinter stocking rate.