The effects of calving to first service interval on reproductive performance in normal cows and cows with postpartal disease

The relationships between the calving to first service interval and several measures of reproductive performance were examined in 1738 lactation records from cows in 32 southern Ontario Holstein herds. Lactation records were divided into three separate health categories based on postpartal disease histories. Relationships between the calving to first service interval and the first service conception rate, number of services per conception and open interval were similar for all three categories. The first service conception rate was lower and the average number of services per conception higher in cows first mated before 60 days when compared to cows first mated after 60 days. The relationship between the calving to first service interval and the open interval indicated that for each day that mating was delayed the open interval was extended by 0.86 days. Overall conception rates may be lower for cows first mated very early or very late, but differences in the overall conception rate were only significant for cows with a reproductive tract infection. Unless very expensive semen is being used, it is suggested that disease free cows be mated at the first heat occurring after 40 days postpartum, and that cows with postpartal disease be mated at the first heat occurring after 60 days postpartum..