Fluctuation in Ewe Liveweight during Periods of Restricted Nutrition Is Influenced by Sire

The ability to maintain weight during adverse seasons is an important characteristic in mature ewes. Ewes that lose less weight will be in better condition at mating and throughout pregnancy resulting in higher fertility, fecundity and lamb survival, and lower ewe mortality. Liveweight data (corrected for greasy fleece and conceptus weights) from mature Merino ewes was analysed to determine factors implicated in differences in liveweight loss during summer, autumn or winter. Liveweight loss during these periods was affected by differences between site (P<0.001) and age of the ewe (P<0.001). There were also significant (P<0.01) differences between sires within breed in the weight fluctuation of their daughters during periods of nutritional restriction. Liveweight change over summer, autumn or winter was not affected by previous reproductive performance, and liveweight change did not affect the subsequent reproductive performance of ewes. These findings indicate it is possible to select ewes more resilient to liveweight loss during periods of limited feed availability without necessarily affecting reproductive performance.