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 wer e 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-da ys in milking interval. The random effects were associated to single l actations. Trends of seasonal effects showed a spring peak for milk ( 206 ml), fat (+11.7 g) and protein (+11 g) yields. Seasonal effects o n fat content were very irregular while those on protein content were small and constant over time. Predicted lactation curves showed an inc reasing effect of age at lambing on all traits. The strong effect of s eason on test day yields suggests further studies on the applicability of test day models in genetic evaluation of dairy sheep breeds with n utrition based on pasture.