(CO)VARIANCE COMPONENT ESTIMATION OF YIELD TRAITS BETWEEN DIFFERENT LACTATIONS USING AN ANIMAL-MODEL

Additive and residual (co)variances between the first four lactations were estimated for milk, fat and protein yields. Results were obtained using restricted maximum likelihood and a multiple trait animal model with different design matrices in three sets of four traits per set. Model included different design matrices in the fixed effects and took into account missing records. An analysis was carried out from record s of 18 658 cows (10 583 for protein yield), and the order of the coef ficient matrix was 118 192 (93 732 for protein yield). A Monte Carlo p rocedure to approximate the traces involving the coefficient matrix of the mixed model equations was used in the EM algorithm. Heritabilitie s for milk yield ranged between 0.22 and 0.32, for fat yield between 0 .20 and 0.30, and for protein yield between 0.19 and 0.26. Genetic cor relations between adjacent lactations were greater than 0.85, with the exception of the third and fourth lactations for protein yield. A sec ond analysis was carried out including the 12 traits and 156 (co)varia nce components simultaneously. In this case, the order of the coeffici ent matrix was 352 116. A result of this second analysis was that the genetic correlations between milk, fat and protein yields do not depen d on the age of the cow.