Retrospective evaluation of factors affecting superovulatory response in embryo production in Simmental cattle

In the present study, it was aimed to investigate the effect of lactation status, days in milk (DIM), follicle stimulating hormone (FSH) dose, and repeated superstimulations on superovulation response and embryo yield in Simmental cattle. In the present study, 193 Simmental breed cattle (lactating, nonlactating, and heifer) were used as donors, of which 149 were superovulated only once and the other 44 were superovulated for 3 times. Progesterone-based estrus synchronization protocol was applied to the donors. Starting from day 7, FSH was given intramuscularly to donors in decreasing doses twice a day for 4 days. The donors were injected with prostaglandin F2α at the 5th FSH treatment and progesterone source was removed 12 h later. Artificial insemination was performed twice after the removal of progesterone source. In the present study, 134 of the 149 donors who underwent a superovulation protocol for the first time responded to superovulation treatment (≥3 corpus luteum (CL); 89.93%) and the mean count of transferable embryos per donor was 5.58. No statistical difference was observed for the counts of CL, total oocyte/embryo, and transferable embryo among heifers, lactating cows, and nonlactating cows. A positive correlation was noted between DIM and embryo yield (P < 0.05). Superovulation response and embryo yield were increased depending on the dose of FSH in cows undergoing superstimulation treatment (P < 0.05). Although no statistical difference was detected between the embryo yields obtained from the first two applications in repeated superovulation treatments, the embryo yield decreased after the 3rd superstimulation. In conclusion, in Simmental breed cows, the embryo yield in superovulation applications was unaffected by lactation status, but was affected by the applied FSH dose and DIM. It was also concluded that the embryo yield decreased after the 3rd application in repeated superovulation treatments