How does maternal genetic merit and country of origin impact lamb performance pre- and post-weaning?

The objective of this study was to investigate the impact of ewe maternal genetic merit and country of origin (New Zealand or Ireland) on lamb growth and performance pre-and post-weaning. The study was conducted from 2016 to 2019, inclusive, and consisted of three genetic merit groups: New Zealand ewes of high maternal genetic merit (NZ), Irish ewes of high maternal genetic merit (High Irish) and Irish ewes of low maternal genetic merit (Low Irish) ewes and their lambs. Each of the genetic merit groups contained 30 Suffolk and 30 Texel ewes, selected based on the respective national maternal genetic indexes; i.e. either the New Zealand Maternal Worth (NZ group) or the Irish eurouro-star Replacement Index (Irish groups). The impact of maternal genetic merit on lamb live-weight, average daily gains, age at drafting, ultrasound scanning, and health traits were analysed using linear mixed models. New Zealand lambs were heavier than High Irish lambs at six weeks post-partum (P < 0.05), Low Irish lambs at weaning (P < 0.001) and than both Irish genetic merit groups at ultrasound scanning (P < 0.001) and at drafting (P < 0.05). New Zealand lambs had greater average daily gains at most time points both pre-and post-weaning compared to High Irish and Low Irish lambs. High Irish lambs had greater average daily gains than Low Irish lambs from birth to drafting and from weaning to drafting (P < 0.001). New Zealand lambs had greater muscle depths (P < 0.001), firmer faecal consistency (P < 0.001) and lower dag scores (P < 0.001) in comparison to both Irish genetic merit groups who did not differ from each other (P> 0.05). High Irish lambs had a higher Nematodirus count (P < 0.001) and lamb quality score (P < 0.05) compared to Low Irish lambs. New Zealand lambs were more likely to be drafted from the system by 1st October compared to lambs in the Low Irish genetic merit group (P < 0.001). Lamb mortality from birth to drafting did not differ between any of the three genetic merit groups (P> 0.05). Overall, few differences are reported between the genetic merit groups pre weaning. However, differences emerged post-weaning between lambs born from ewes of high and low maternal genetic merit and between animals of NZ and Irish origin, demonstrating the potential benefit of their strategic use in the future.