Effects of oestrus synchronisation and fixed-time artificial insemination on the reproductive performance of dairy heifers

Aim. To compare the reproductive performance of heifers after oestrus synch ronisation and fixed-time artificial insemination with non-synchronised hei fers bred by herd sires. Methods. Heifers from 10 spring-calving herds were randomly divided into tw o groups by herd, breed and age. Heifers in one group (the synchronised gro up, n = 478) were synchronised with a combination of progesterone, oestradi ol benzoate and PGF(2 alpha), and inseminated 50-54 hours after progesteron e treatment. Returns to first service were resynchronised with progesterone treatment 16-21 days after the fixed-time artificial insemination. Heifers in the other group (the control group, n = 470) did not receive any treatm ent and were bred by herd sires, Results. The conception rate of synchronised heifers to the fixed-time arti ficial insemination was 51.2% and to the artificial insemination after resy nchronisation 40.4%. The pregnancy rate at the end of the breeding season t vas lower (p < 0.001) for the synchronised (92.9%) than for the control (97 .2%) group. The interval from start of breeding to calving was earlier for synchronised (295.9 +/- 22.5 days, mean +/- s.d.) than for control (298.5 /- 17.3 days) heifers. Conclusion. Results from this study indicate that the oestrus synchronisati on programme used in the present study can reduce reproductive performance by increasing the empty rare compared with natural mating.