Supplementing treated anoestrous dairy cows with progesterone does not increase conception rates

Aim: To determine whether conception rates of anoestrous dairy cows treated with progesterone and oestradiol benzoate (ODB) could be increased by trea ting them with additional progesterone following insemination at the induce d oestrus. Methods: Cows which had not been detected in oestrus for at least 21 days a fter calving in 18 herds were confirmed anovulatory anoestrus (AA) by veter inary examination, due to the absence of a detectable corpus luteum in the ovaries. All cows were treated with intra-vaginal progesterone (CIDR insert ) for 6 days and injected with 1 mg ODB 24 h after insert removal (Day 0). Only cows which were seen in oestrus on Days 0, 1 or 2 were enrolled in the trial. These cows were either treated with a second CIDR insert on Day 8, for 7 days (P4+; n=422), or remained untreated (Control; n=756). Milk proge sterone concentrations were measured in a subset of enrolled cows (n=669) o n Day 8 to determine the proportion of cows that ovulated following the ind uced oestrus. Results: Conception rates to first insemination were similar in P4+ and Con trol cows (40.3% and 37.2%, p=0.59). Of cows which had milk progesterone co ncentrations measured on Day 8, 78.6% displayed oestrus and ovulated, (rang e: 53.8% to 94.6% among herds). Of the cows that ovulated, conception rate to first insemination was 46.8% and 43.5% in P4+ and Control cows, respecti vely (p=0.86). Conclusion: Conception rates to first insemination in AA cows treated with progesterone and ODB were not increased by progesterone supplementation usi ng CIDR inserts following insemination.