Milk yield adjustments for milking length and age-parity-lambing month interaction in Sarda dairy sheep

Milk yield adjustments for milking length and age-parity-lambing month interaction were estimated to allow effective comparisons between yields and with the perspective of improving the reliability of the genetic evaluation of Sarda dairy ewes. The analysis included 671 404 records used for the genetic evaluation round of the year 1995. Predicted milk yields for levels of milking length were obtained by applying a model containing the maximum test day yield as covariate. This approach was used to account for different production capabilities and to avoid correction for factors other than duration. The predicted values were interpolated by third degree polynomial function to smooth differences between classes and multiplicative coefficients estimated by using base milking length (162 days). On adjusted milk yields a repeated animal model, including as fixed effects the flock year-age-parity and year age-parity-lambing month interactions, was applied. For each record the sum of fixed effect solutions was calculated. Averages of fixed effect sums were used to estimate multiplicative coefficients, the base being associated to a level defined by lactations of fourth age class, third-fourth parities and August-November lambing months. The new milk trait, defined as mature ewe equivalent (MEE), could be used by breeders to compare milk yields within flock-year and to make more accurate culling choices. The higher homogeneity of means and standard deviations within age-parity classes seems interesting for genetic evaluations based on MEE rather than milk yield adjusted for milking length only. ((C) Elsevier/Inra.).