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 yie lds and with the perspective of improving the reliability of the genet ic evaluation of Sarda dairy ewes. The analysis included 671 404 recor ds used for the genetic evaluation round of the year 1995. Predicted m ilk yields for levels of milking length were obtained by applying a mo del 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 difference s between classes and multiplicative coefficients estimated by using b ase milking length (162 days). On adjusted milk yields a repeated anim al model, including as fixed effects the flock year-age-parity and yea r age-parity-lambing month interactions, was applied. For each record the sum of fixed effect solutions was calculated. Averages of fixed ef fect 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 mil k trait, defined as mature ewe equivalent (MEE), could be used by bree ders to compare milk yields within flock-year and to make more accurat e culling choices. The higher homogeneity of means and standard deviat ions within age-parity classes seems interesting for genetic evaluatio ns based on MEE rather than milk yield adjusted for milking length onl y. ((C) Elsevier/Inra.).