The reproductive performance of anoestrous dairy cows following treatment with progesterone and oestradiol prior to the start of mating

Aims: To determine the reproductive performance of cows diagnosed as anoest rus prior to the planned start of mating (PSM) when they were either treate d when first diagnosed, or left untreated until 16 days after the PSM. Methods: A clinical trial was conducted during the 1996/97 and 1997/98 bree ding seasons involving 823 anoestrous dairy cows in 14 herds. On Day-8 (PSM = Day 0), cows in one group (Treated) were each treated with an intravagin al device containing 1.9 g of progesterone (CIDR). The CIDR device was remo ved on Day-2, and on Day-1 each cow was injected intramuscularly with 1 mg oestradiol benzoate. Cows in the second group (Control) remained untreated at the time of first examination. All cows detected in oestrus after the PS M were mated by artificial insemination (AI) or a bull. Sixteen days after the PSM, all cows that had not been mated were presented for veterinary exa mination, and those which were still classified as anoestrus were treated w ith the previously described CIDR regimen. Pregnancy status and approximate date of conception were determined by palpation per rectum 10-13 weeks aft er the PSM or 6 weeks after the end of the mating period. Results: Treatment of anoestrous cows 8 days before the PSM significantly i ncreased the number of cows detected in oestrus (95.0% vs 63.1%; p < 0.001) and conceiving (59.5% vs 38.8%; p < 0.001) during the first 21 days of mat ing, and reduced the interval from PSM to conception by 7.5 days (p < 0.001 ). There was no significant difference between the conception rate of cows mated following the CIDR treatment regimen compared to cows mated at their first spontaneous oestrus after calving (52.4% vs 58.3%; p = 0.143). Conclusion: Diagnosis and treatment of anoestrous dairy cows prior to the s tart of mating significantly improves their reproductive performance under the seasonal mating conditions typical of spring-calving New Zealand dairy herds.