The objective of this study was to investigate the impact of the ewe’s maternal genetic merit and country of origin (New Zealand or Ireland) on ewe reproductive, lambing and productivity traits. The study was performed over a four year period (2016 to 2019) and consisted of three genetic groups: high maternal genetic merit New Zealand (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 New Zealand Maternal Worth (New Zealand 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 were analyzed using linear mixed models. For binary traits, the impact of maternal genetic merit on reproductive traits such as conception to first AI service; lambing traits such as dystocia, perinatal lamb mortality and productivity traits such as ewe survival were analyzed using logistic regression. New Zealand 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% CI: 1.89 to 11.55; P<0.001) and 6.54 (95% CI: 2.56 to 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. New Zealand 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). New Zealand ewes tended to be more likely to survive from one year to the next compared to 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 favourable improvements in reproductive, lambing and productivity traits at farm level. Overall, results demonstrate the suitability of NZ genetics in an Irish production system.

The aim of this study was to investigate the impact of ewe genetic merit on ewe performance and efficiency parameters. The study consisted of three genetic merit groups (New Zealand (NZ), High Irish and Low Irish) and ran from 2016 to 2019, inclusive. Each genetic merit group contained 30 purebred Suffolk and 30 purebred Texel ewes, that were selected based on their maternal genetic indexes in their country of origin namely Ireland (€uro-star Replacement index) or New Zealand (New Zealand Maternal worth). Ewe body condition score (BCS), ewe body weight (BW), milk yield, milk composition, dry matter intake (DMI) and efficiency parameters were all analysed using linear mixed models. Ewe BW was similar across all genetic merit groups at each time point (P>0.05). In comparison to both High and Low Irish ewes, NZ ewes had a higher BCS at mating, mid-pregnancy, lambing, wk 10 post-lambing (PL, P<0.05). Ewe BW change was similar across genetic merit groups, except between mating and mid-pregnancy where ewe BW loss was greater for NZ ewes than Irish ewes (P<0.05) and between wk 6 PL and wk 10 PL where NZ ewes gained BW and High and Low Irish ewes lost BW (P<0.01). Ewe milk yield, milk fat, total solids and gross energy content was superior for milk produced by NZ ewes at wk 6 PL in comparison to milk produced by High Irish and Low Irish ewes (P<0.01). New Zealand ewes produced a greater quantity of milk solids/kg of BW at wk 6 PL compared to High Irish ewes (P<0.01), while Low Irish ewes did not differ from either NZ or High Irish (P>0.05). Low Irish ewes had a greater daily DMI than High Irish ewes in late lactation (wk 10 PL, P<0.05) and had a greater DMI/kg of ewe BW compared to the High Irish ewes at the same time point (P<0.05). New Zealand ewes weaned a litter BW equivalent to 60.4 % of their mating BW, which was more than the Low Irish ewes who weaned 57.1 % of the ewe’s BW at mating (P<0.01), while the High Irish ewes did not differ from either the NZ or Low Irish ewes at 59.3 % of the ewe’s BW at mating (P>0.05). This paper presents a range parameters across ewes of high and low genetic merit, demonstrating the ability to achieve gains through selection of animals of high genetic merit. Sheep producers should consider genetic indexes as a tool to assist in the decision making process of selecting replacement ewes and/or breeding rams, once satisfied the animal is correct and meeting the breeding objectives of the system.

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