Ewe lamb live weight and body condition scores affect reproductive rates in commercial flocks

The objective of this study was to determine the relationships between ewe lamb live weight and body condition score immediately prior to breeding with fertility (ewes pregnant per 100 ewes bred) and reproductive rates (fetuses per 100 ewes bred). Over 2 years, ewe lambs on seven commercial sheep farms in the North Island of New Zealand were monitored during the breeding period until pregnancy diagnosis. Live weight and body condition score were recorded prior to breeding. Fertility rates increased with live weight up to 47.4 kg but did not increase above this (P > 0.05). Reproductive rate peaked for ewes in the 47.5-52.4 kg breeding live weight category at 138% (133%-143%). Ewe fertility peaked at a body condition score (BCS) of 3.5 (90% [88%-91%]) while reproductive rates peaked at a BCS of 3.0 (130% [127%-133%]). The apparent plateauing of the relationship indicates there is a point at which no further benefits are gained from increasing live weight or BCS.