Genetic analyses of fertility parameters and their relations to milk yield of Holstein-Friesian cows in Tunisia

More than 49 000 lactations and reproductive data of cows, recorded between 1995 and 2001 on Tunisian Holstein-Friesian dairy cattle, were used in this study. Fertility parameters: days to first service (DTFS), days open (DOP) and calving interval (CI) averaged 85, 157 and 417 days respectively. Heritability estimates of these traits are low: 0.03, 0.06 and 0.09 respectively, whereas that of milk is equal to 0.22. Correlation between fertility parameters and milk yield is positive. According to these results, the strategy of genetic evaluation is discussed. Our results showed that if we consider DOP as a fixed effect, in the evaluation model, genetic evaluation of the animals will improve.