Abstract

Scanned, twin-bearing mixed aged ewes (n=1276) were set-stocked (7.5 ± 0.1 ewes ha-1) over the lactation period at either high or low condition score (CS) (2.51 vs 1.52) and high or low herbage mass (HM) (1160 vs 880 kg DM ha-1 ) in an experiment replicated on 5 farms in Wairarapa. Three farms lambed early (27 August to 4 September 1997) and were summer-dry and two lambed later (22 to 27 September 1997) and were summer-wet. High ewe CS may have improved lamb survival (167 vs 150%, P=0.13) through reduction in estimated lamb mortality (17 vs 25%, P<0.01) on late lambing farms where weather conditions were adverse at lambing, but had no effect on early lambing farms where lambing conditions were more favourable. Ewe CS had no effect on either lamb or ewe LWG. High HM may have reduced lamb mortality on early lambing farms (10 vs 14%, P<0.05) where ewes were under greater nutritional stress than on late farms. Additional HM at set-stocking increased lamb LWG up to docking by 11 g d-1 per 100 kg DM ha-1 increase (P<0.03) on early farms but had no effect on late farms. Lamb LWG from docking to weaning was unaffected by set-stocking HM. The overall effect of an increase in set-stocking HM by 100 kg DM ha-1 was to increase lamb weaning weight by 2 kg on early farms. Additional HM at set stocking increased ewe LWG from birth to docking by 33 g d-1 per 100 kg DM ha-1 increase (P<0.001) but decreased LWG from docking to weaning by 18 g d -1 per 100 kg DM ha-1 increase. This response was similar on early and late lambing farms. On early farms there was a net increase in ewe liveweight at weaning of 1.6 kg for each 100 kg DM ha -1 increase in lambing HM.

MG, Lambert, AJ Litherland, and PN McLaren

Proceedings of the New Zealand Society of Animal Production, Volume 59, , 104-107, 1999