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Various factors influencing reproduction in dairy Holstein cows were routinely evaluated and genetic parameters were estimated for four traits for assessing fertility of artificially inseminated cows: Calving to first service interval (CFSI), calving interval (CI), calving to conception interval (CCI), and number of services per conception (NSC). Data used in this investigation consisted of records of insemination and calving events on Tunisian Holstein cows. Records were registered from 1994 to 2003 in 150 herds to study the effects of non-genetic factors and estimate the heritabilities of those fertility traits. The factors examined were: month and year of calving, herd, parity, and year-month of calving. The effect of month and year of calving (or insemination), herd, parity and year-month of calving were included in the model and were significant (P < 0.01) except for the number of lactations that does not have an effect on the number of services per conception. A decreasing efficiency in cow fertility was observed over the last years, with a longer day for first service interval. Heritability for fertility traits was low ranging from 0.027 for NSC to 0.067 for CI. The results suggested that more attention should be paid to herds with too low fertility traits and that monitoring/alert and intervention schemes should be tested in research/action approaches.

Phenotypic and genetic parameters of reproductive traits in Tunisian Holstein cows