Adult Merino ewes can be bred for live weight change to be more tolerant to climate change

Climate change is going to complicate sheep management in Mediterranean climates due to increased variation in the supply of pasture and crop stubbles for grazing during summer and autumn. Farmers will rely more on providing supplementary feed which is expensive. Therefore liveweight loss during periods of low nutrition and subsequent liveweight gain are likely to be economically important traits. We estimated the genetic parameters for liveweight loss and liveweight gain on 2700 fully pedigreed 2 to 4 years old Merino ewes. When data for ewes from all ages was analysed together with age fitted as a fixed effect, liveweight gain had a heritability of 0.18 whilst liveweight loss had a heritability of 0.06. Loss and gain also had a moderate negative genetic correlation, showing that high weight loss was related to high weight gain. When liveweight change is analysed to be a different trait at each age using a multivariate model, heritability for live weight gain was 0.37 for ewes aged 2 years and 0.20 for ewes aged 3 and 4 years. Heritability for live weight loss was around 0.15 for all ages. These results suggest that liveweight change could be included in breeding programs to breed adult Merino ewes that are more tolerant to variation in feed supply.