Efficacy of a treatment with hCG 4 days after AI to reduce pregnancy losses in lactating dairy cows after synchronized ovulation.

Content The objective of the study was to investigate whether a treatment with hCG 4 days after AI could reduce pregnancy losses in lactating dairy cows. Cows of a dairy herd presented to the veterinarian in a fixed reproductive management protocol were treated with an Ovsynch protocol if no corpus luteum (CL) could be palpated per rectum (Group OV). Cows with a CL received cloprostenol (0.15 mg). After 2 days, these cows were treated with buserelin (0.01 mg) and received timed AI 16-20 h later (Group PG). In both treatment protocols, cows were assigned to two groups to receive 2500 IU of hCG i.v. 4 days after AI or to serve as untreated controls (Groups OV-hCG, OV-Control, PG-hCG and PG-Control). Pregnancy diagnosis was carried out 27 days after AI via ultrasonography and 39 days after AI by rectal palpation. Pregnancy losses were defined as cows being pregnant on day 27 but not pregnant on day 39 after AI. Pregnancy rate (PR) by day 27 did not differ among the four groups (35.4, 35.0, 37.0 and 38.0% for Groups OV-hCG, OV-Control, PG-hCG and PG-Control, respectively). Pregnancy losses between day 27 and day 39 after AI were smaller in hCG treated animals in summer but not in autumn and spring. Pregnancy rate by day 39 after AI was higher in PG than in OV groups, but independent of hCG-treatment. In conclusion, treatment with hCG 4 days after AI did not significantly increase PR on 39 days after AI. A positive effect of hCG on pregnancy losses during the summer months warrants further investigation.