The impact of maternal genetic merit and country of origin on ewe reproductive performance, lambing performance, and ewe survival.

The objective of this study was to investigate the impact of the ewe's maternal genetic merit and country of origin [New Zealand (NZ) or Ireland] on ewe reproductive, lambing, and productivity traits. The study was performed over a 4-yr period (2016-2019) and consisted of three genetic groups: high maternal genetic merit (NZ), high maternal genetic merit Irish (High Irish), and low maternal genetic merit Irish (Low Irish) ewes. Each group contained 30 Suffolk and 30 Texel ewes, selected based on the respective national maternal genetic indexes; i.e., either the NZ Maternal Worth (NZ group) or the €uro-star Replacement index (Irish groups). The impact of maternal genetic merit on reproductive traits such as litter size; lambing traits such as gestation length, birth weight, lambing difficulty, mothering ability; and productivity traits such as the number of lambs born and weaned was analyzed using linear mixed models. For binary traits, the impact of maternal genetic merit on reproductive traits such as conception to first artificial insemination (AI) service; lambing traits such as dystocia and perinatal lamb mortality; and productivity traits such as ewe survival was analyzed using logistic regression. NZ ewes outperformed Low Irish ewes for conception to first AI (P < 0.05) and litter size (P = 0.05). Irish ewes were more likely to suffer from dystocia [6.84 (High Irish) and 8.25 (Low Irish) times] compared to NZ ewes (P < 0.001); birth weight and perinatal mortality did not differ between groups (P > 0.05). Lambs born from NZ ewes were 4.67 [95% confidence interval (CI): 1.89-11.55; P < 0.001] and 6.54 (95% CI: 2.56-16.71; P<0.001) times more likely to stand up and suckle unassisted relative to lambs born from High or Low Irish ewes, respectively. NZ and High Irish ewes had a greater number of lambs born and weaned throughout the duration of the study compared to their Low Irish counterparts (P<0.001). NZ ewes tended to be more likely to survive from one year to the next compared with Low Irish ewes (P=0.07). Irish ewes of high maternal genetic merit outperformed their low counterparts in total number of lambs born and weaned per ewe, but performance did not differ across other traits investigated. This highlights the importance of continuous development of the Irish maternal sheep index to ensure favorable improvements in reproductive, lambing, and productivity traits at the farm level. Overall, results demonstrate the suitability of NZ genetics in an Irish production system.