GENETIC AND PHENOTYPIC PARAMETERS FOR MILK-PRODUCTION AND FERTILITY TRAITS IN UPGRADED DAIRY-CATTLE

Genetic parameters for the relation between milk production and fertility were estimated in the Dutch Black and White dairy cow population, a crossbred population of the Holstein Friesian and Dutch Friesian breeds. In the analyses, 82659 records on first lactation production and fertility were used, containing 13480 progeny from 1011 young bulls and other progeny descending from proven bulls. Restricted Maximum Likelihood was used to estimate variance components for effects of sire of cow and residual. Generalized Least Squares estimates showed a positive breed effect of Holstein Friesians (HF) over Dutch Friesians of about 500 kg for 305 days milk production, and a negative HF-breed effect on both 56 days-nonreturn and calving percentage of eight percent points. Heritability estimates for milk production traits were 0.48, 0.36, and 0.33 for 305 days milk, fat, and protein yields, respectively. Heritability estimates for fertility traits were 0.04, 0.03, 0.04, 0.05 and 0.02 for interval calving to first insemination, calving interval, 56-days nonreturn, calving percentage after first insemination and interval from first insemination to conception, respectively. Phenotypic correlations between milk production traits and fertility traits showed a negative association (-0.05 to -0.18). Genetic correlations showed a stronger negative association (-0.14 to -0.62). Negative genetic associations of fertility traits with protein yield were somewhat stronger than those with milk yield.