GENETIC-STUDY OF FERTILITY TRAITS AND PRODUCTION IN DIFFERENT PARITIES IN ITALIAN FRIESIAN CATTLE

A data set of production records with breeding information was used to analyse the relationship between open period, days to first breeding, conception rate at first service, number of services per conception a nd 305 day milk yield adjusted for age/month of calving and open perio d in the Italian Friesian Cattle Breed. Separate analyses were perform ed for the first three parities. Heritability estimates for reproducti ve traits varied from .01 to .03 and for productive traits from .16 to .22 depending on parities. Repeatabilities for fertility traits were .02 to .08 while for milk yield they were between .49 and .59. Open pe riod and days to first service were found to be highly correlated (gen etic correlation: +.70/+.92) as were conception rate at first service and number of services per conception (-.98). An antagonistic genetic relationship was found between all reproductive traits considered and production. The magnitude of the antagonistic genetic association betw een production and fertility indicate that genetic deterioration of fe rtility is to be expected if selection pressure continues to be applie d to milk production only. For multiple trait selection, the reproduct ive measures which complement each other are days to first service and first service conception rate (or number of services per conception).