EFFECT OF HOLSTEIN CROSSBREEDING IN THE FRENCH BLACK-AND-WHITE CATTLE POPULATION

Heterosis and recombination losses of Holstein x European Black and White cattle were estimated for milk, fat, and protein yields and for fat and protein contents from about 12.4 million records collected in France on about 5.6 million cows between 1975 and 1992. The Holstein percentage reached almost 100% by 1980 for Al bulls and increased from 5% in 1970 to 83% in 1990 for cows. Crossbreeding parameters, including a nonadditive effect that was due to the breed composition, were estimated with an animal model. Heterosis reached 2 to 2.5% for yield traits and was very low for fat and protein contents. For yields, estimates of recombination losses were negative and reached 40 to 86% of heterosis. Recombination losses seemed to be slightly positive for contents. For yield traits, omission of these crossbreeding parameters (as is generally the case) for genetic evaluation led to an overestimation of the genetic difference between strains by 10% and to a downward bias of the within-strain genetic trend by 10 to 20%.