COMPARISONS BETWEEN GENETIC VARIANCES ESTIMATED FROM DIFFERENT TYPES OF RELATIVES IN DAIRY-CATTLE

Genetic variances were estimated from different types of relatives for a data set of 19038 first lactation fat yield (FY) and fat concentration (FC) records. For FY, h2 estimates were 0.377, 0.322 and 0.377 from an animal model, a sire model and a model using only female relationships. The corresponding estimates for FC were 0.632, 0.628 and 0.610. Regarding sires with most progeny in the data set as levels of a fixed effect slightly increased h2 estimates, most likely through accounting for selection of proven sires. Statistical models were presented to account for heterogeneous genetic variances for males and females in the prediction of breeding values or in estimating variance components. Simultaneously estimating genetic variances for FY from paternal half-sibs, maternal half-sibs, and daughter-dam comparisons, resulted in heterogeneous genetic variance estimates from male v. female comparisons and similar variance estimates from mhs and dd comparisons. For FC, h2 estimates from different types of relatives were similar. Dam-daughter comparisons provide 0.75 to 0.80 of the information on heritability from female relationships and provide 0.42 to 0.55 of the total information on heritability.