77 REPRODUCTIVE PERFORMANCE OF DAIRY COWS DIFFERING IN THE INTERVAL FROM CALVING TO THE FIRST OVULATION IN THE POSTPARTUM PERIOD

In recent years, reproductive performance of dairy cows has declined worldwide. The reproductive characteristics of dairy cows should be evaluated to improve their fertility. Dochi et al. (2010) had reported that dairy cows that exhibited early first ovulation gave a low milk yield, had an early recovery of body condition score (BCS) in the postpartum period and a shorter number of days open. The objective of this study was to evaluate the effect of BCS on the functional recovery of reproduction after the birth of the calves. In this study, lactating Holstein cows were placed in free-stall housing equipped with an automatic milking system. The data presented in this study were collected from 48 cows that had calved between December 2007 and October 2010 with an average parity of 3.4 (range 2–6). The reproductive performance and the BCS during the different intervals between calving and the first ovulation were analysed using ANOVA. The conception rate at the first service was 38.1%. The average milk yield (305 days) was 12 299 kg. The first ovulation and oestrus were determined by ultrasonography. The results of the different intervals to the first ovulation are presented in Table 1. The average interval from the start of days in milk (DIM) to the first ovulation, first oestrus and first service; the number of days open; the number of services per conception and the milk yield (kg day–1, by 90 DIM) were 37.4, 54.7 and 110.3 days; 168.2 days open; 2.5 times; and 42.1 kg day–1, respectively. The cows that exhibited early first ovulation (≤21 DIM) in the postpartum period had significantly shorter intervals between the start of DIM and the first oestrus (P  150 DIM). In conclusion, these results suggest that the delay to the first ovulation in the postpartum period tended to have delayed the oestrus expression in the cows. Moreover, the low level of BCS in the peripartum period, regardless of the number of days of the first ovulation and the first oestrus, potentially influenced the prolongation in the number of days open. To improve the fertility of the cows, it is important to elucidate the factors affecting the fluctuations in the BCS during the peripartum period. Table 1.Reproductive performance of dairy cows differing in interval to postpartum first ovulation