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

Genetic parameters for the relation between milk production and fertil ity were estimated in the Dutch Black and White dairy cow population, a crossbred population of the Holstein Friesian and Dutch Friesian bre eds. In the analyses, 82659 records on first lactation production and fertility were used, containing 13480 progeny from 1011 young bulls an d other progeny descending from proven bulls. Restricted Maximum Likel ihood was used to estimate variance components for effects of sire of cow and residual. Generalized Least Squares estimates showed a positiv e breed effect of Holstein Friesians (HF) over Dutch Friesians of abou t 500 kg for 305 days milk production, and a negative HF-breed effect on both 56 days-nonreturn and calving percentage of eight percent poin ts. Heritability estimates for milk production traits were 0.48, 0.36, and 0.33 for 305 days milk, fat, and protein yields, respectively. He ritability 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 in terval from first insemination to conception, respectively. Phenotypic correlations between milk production traits and fertility traits show ed a negative association (-0.05 to -0.18). Genetic correlations showe d a stronger negative association (-0.14 to -0.62). Negative genetic a ssociations of fertility traits with protein yield were somewhat stron ger than those with milk yield.