Reproductive performance of commercial sheep flocks in South Island districts

Abstract

Relationships between reproductive performances and liveweights recorded over the period from joining to tailing in sheep flocks on 21 farms between 1976 and 1978 were examined. Each kg difference between farms in mean pre-flushing liveweight of their flocks was associated with a difference of 0.030 (SE = 0.005) in mean ovulation rates and a kg liveweight change during flushing was associated with a change in ovulation rate of 0.071 (SE = 0.013). The correlation between the 2 estimates was 0.189 (NS). On a within-flock basis, ovulation rate changed by 0.016 (SE = 0.002) for every 1 kg difference in ewe liveweight at the end of Period 1 (16–18 days) of joining, with significant variation between years and between districts within years. Ewe barrenness (excluding animals not marked at joining) was highly correlated (r = 0.63, P<0.01) with partial failure of multiple ovulation in ewes with 2 corpora lutea. An increase of 10 ovulations per 100 ewes was associated with an extra 6.1–6.9 lambs born per 100 ewes lambing and 5.2–5.7 lambs tailed per 100 ewes joined.