High body condition score of 3.5 - 4.0 in ewes at mating, scanning and in lactation is associated with long survival rates and high lifetime productivity: A seven-year prospective longitudinal study of 6000 ewes from eleven flocks in England.

Improving the lifetime productivity of ewes is important to improve efficiency and reduce greenhouse gas emissions from sheep farming. In 2017, eleven English sheep flocks with 6000 nulliparous ewe lambs or shearlings were enrolled into a seven-year prospective longitudinal study to investigate lifetime performance of ewes over six parities. Multivariable statistical models were used to investigate productivity and survival of ewes per year and over six-years of production. The key results were: lifetime performance of ewes was dependent on their survival for all six parities; ewes mated as ewe lambs (6-7 months old) produced approximately one lamb more over their lifetime than ewes mated as shearlings (18-20 months old). Ewes that were body condition score ((BCS) (on a 1-5 point scale) 2.0 at parturition were four times as likely to die on farm as ewes with BCS > 2.0. Survival, litter size, lamb weight gain to eight-weeks and to weaning, increased as ewe body condition pre-mating, at parturition and in lactation increased from BCS 2.5 to BCS 3.5-4.75 (dependent on the outcome). For most measures of productivity production plateaued between BCS 4.0 and 4.75. This is the first study to provide a numeric estimate of when ewe productivity plateaus. This is the longest prospective study of ewe performance in England, and it highlights that maximum productivity occurs in sheep with a body condition score of 3.5 - 4.0, higher than previously hypothesised. The results can be used by the sheep industry together with input factors, such as farm location, sheep breed, nutrition and other costs, to optimise flock specific lifetime performance of ewes.