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.