Effect of oestrus synchronisation through ovulation delay by vaccination against foot‐and‐mouth disease in Hanwoo (Bos taurus coreanae) cows

Background In Korean cattle, after foot‐and‐mouth disease (FMD) vaccination, anovulation increases, acute immune response is stimulated. Objective Here, we aimed to improve the fertility rate by ovulation delay caused by the foot‐and‐mouth disease vaccine. Methods 160 cows (control, FMD, FMD+Gn250 and FMD+Gn500 groups, with 40 cows each) were used. We analysed the ovulation delay, ovulation rate, conception rate and acute‐phase immune responses. Results In the group vaccinated only with FMD, the average follicle size was maintained at 12 mm and ovulation was delayed. The ovulation rate of the FMD+Gn500 group (500 μg gonadotropin‐releasing hormone (GnRH) injections 3 days after the FMD vaccination) was the highest at 81.8%. The ovulation rate of the FMD+Gn250 group (250 μg GnRH injections 3 days after FMD vaccination) was 54.5%, and that of the control group (not FMD vaccinated) was 53.3%. The conception rate was 52.5% (19/40) in the control group, 37.5% (15/40) in the FMD+Gn250 group, and 67.5% (27/40) in the FMD+Gn500 group. Analysis of acute‐phase immune response revealed that the plasma contents of haptoglobin and serum amyloid A increased up to 7 days after vaccination against FMD in all the experimental groups, except the control group. Conclusions We concluded that ovulation delay can be employed to improve conception rate after FMD vaccination through a modified ovulation synchronisation method with GnRH. The purpose of this study is to improve the fertility rate by ovulation delay caused by foot‐and‐mouth disease vaccination. We figure out that ovulation delay can be employed to improve conception rate after FMD vaccination through a modified ovulation synchronization method with 500 μg of GnRH administration.