ESTIMATING LACTATION CURVES AND SEASONAL EFFECTS FOR MILK, FAT AND PROTEIN IN SARDA DAIRY SHEEP WITH A TEST DAY MODEL

Actual and predicted lactation curves per age at lambing and seasonal effects for milk, fat and protein yields, fat and protein contents were obtained fitting a mixed model on 10866 monthly test day records of 1740 lactations of Sarda ewes. The model included as fixed effects the interactions flock-year-month of test day and age at lambing class-days in milking interval. The random effects were associated to single lactations. Trends of seasonal effects showed a spring peak for milk (+ 206 ml), fat (+11.7 g) and protein (+11 g) yields. Seasonal effects on fat content were very irregular while those on protein content were small and constant over time. Predicted lactation curves showed an increasing effect of age at lambing on all traits. The strong effect of season on test day yields suggests further studies on the applicability of test day models in genetic evaluation of dairy sheep breeds with nutrition based on pasture.