GENETIC-ANALYSIS OF CONCEPTION RATE IN FRENCH HOLSTEIN CATTLE

Genetic parameters for conception Tate in Holstein cattle were estimated from insemination data collected in western France in 1987-88. Data included 513 020 inseminations of 250 215 lactating cows. Sire, service bull, herd and cow variance components were estimated with the ''tilde-hat'' method. Both linear and threshold models were used and provided very similar results for the fixed effects. Conception rate was lowest in latest parities, before 60 days postpartum, in winter and on Mondays. With the linear model, the estimated heritability and repeatability of conception rate were 2 and 3.2%, respectively, and the service bull and herd components contributed 0.8 and 1.1% of the total variance, respectively. All variance components were 60% greater from the threshold model. The correlation between male and female fertility was small and slightly negative (-0.11). In spite of a low heritability, the genetic variability of female fertility was large, with a genetic coefficient of variation of 14%. The genetic correlations between conception rate at first insemination and 100-day yield traits were estimated by REML on 83 606 first lactation data. They were found to be antagonistic, with -0.60, -0.42 and -0.36 for milk, fat and protein yields, respectively, whereas the phenotypic correlations were only slightly negative (-0.02 to -0.04).