Estimates of Genetic Parameters for Fertility Traits of Italian Holstein-friesian Cattle

Data from insemination and calving events of Italian Holstein cows and heifers collected from January 1996 until December 2002 were used to estimate phenotypic and genetic parameter for some fertility traits. A validation procedure of the data based on gestation length and information on service sire was used. According to these procedure, in Italy 75.9 % of the calvings are associated to service or inseminations events. Days to first service (DTPS), calving interval (CI), number of service per conception (NSC) and non return rate at 90 days (NRR90) were the main traits analysed. The effect of month and year of calving (or insemination), of sampling bull code, of age of cow and of herd-year-season of calving were included in the model and were significant for all the traits analysed. A decreasing efficiency in cow fertility was observed over the last 5 years, with a longer days to first service interval and a higher proportion of cows being re-bred after 90 days. Different data sets were successively defined according to the parities in order to validate the hypothesis that different parities have to be considered as different traits. Heritabilities for the five fertility traits were low ranging from 0,014 for NRR90 to 0,065 for CI. Estimates of c2 for score traits (NSC, NRR56 and NRR90) ranged from 0,010 to 0,025 and were lower than those for CI and DTPS. Genetic correlation were high between traits related to time period but were moderate between those traits and score traits. Heritabilities of interval traits (CI, DTPS) vary over parities, with some indication that higher parities show higher estimates. Results in terms of genetic correlations confirmed the high relationships with interval traits between parities.