Fecundity and ewe liveweight affect ewe wastage, productivity and greenhouse gas emissions

Abstract

Ewe wastage, defined as ewe death and failure to rear lambs, reduces productivity, profitability and ecoefficiency in New Zealand sheep systems. National survey data identified ewe fecundity and ewe liveweight as significant drivers of wastage, but their whole-farm impacts are poorly quantified. This study modelled the effects of changes in ewe liveweight (−10 to +10 kg) and fecundity (−20% to +20% scanning percentage) on flock dynamics, production, gross margins and greenhouse gas (GHG) emissions, assuming a constant annual feed supply. National average performance was represented by a fecundity of 184%, ewe liveweight of 66.4 kg, ewe mortality of 5.5% and 14.2% of ewes rearing no lambs.
Increasing ewe liveweight from 56.4 to 76.4 kg reduced  ewe mortality from 6.4% to 4.6% and failure to rear lambs from 18.6% to 9.8%, increasing weaning rate from 131% to 150%. Increasing fecundity from 164% to 204% reduced ewe mortality from 6.1% to 4.9%, reduced ewes rearing no lambs from 17.8% to 10.6% and increased weaning rate from 117% to 166%. Under constant feed supply, higher ewe liveweight resulted in little change in lambs sold (≤20 head), whereas higher fecundity increased lambs sold by approximately 480 head per farm. Gross margin per ewe increased from
$102 to $125 with increasing liveweight and from $86 to $145 with increasing fecundity. Total GHG emissions declined by 5–6%, with emissions intensity reduced by up to 18% per unit of product. Reducing ewe wastage through improved fecundity delivers larger system level gains than increasing liveweight alone, although both pathways improve productivity, profitability and emissions efficiency.