Attainment of puberty by ewes in the first year of life is associated with improved reproductive performance at 2 years of age

• Ewes attaining puberty in their first year perform better at 2 years of age.
• Selection of replacement ewes on this basis may be beneficial for flock performance.
• The proportion of ewe lambs attaining puberty each year was highly variable.
• This variability was not entirely explained by differences in live weight.

This study was conducted to investigate the effect of attaining puberty in the first year of life on future reproductive performance in ewes. Records were collected from 2091 ewes born between 2005 and 2009. In the first breeding season of life, receptivity to the ram was monitored to determine whether ewe lambs attained puberty or not. Ewes were then mated in order to produce a lamb at 2, 3 and 4 years of age and the following traits were measured each year: ovulation rate (OR), number of foetuses present at scanning (NLS), number of lambs born (NLB) and live weight at various time points. The percentage of ewe lambs attaining puberty was highly variable between years (p < 0.001) and this variability was not explained by differences in live weight. Attainment of puberty in the first year of life increased NLB at 2 years of age (p < 0.001), largely due to an increase in OR (p < 0.01). Ewes that attained puberty in their first year were more likely to become pregnant at 2 years of age (p < 0.01) and produced more multiple births and fewer singletons (p < 0.05). These differences were not maintained at 3 and 4 years of age although differences in live weight remained (p < 0.001). These results demonstrate that attaining puberty in the first year of life improves reproductive performance as a 2 year old, increasing NLB by 20 lambs per hundred ewes and reducing the incidence of non-pregnant ewes. This has implications for improving the efficiency of sheep production on-farm.