Induction and formation of accessory corpus luteum after artificial insemination (AI) might increase pregnancy rate per AI in heat stressed dairy cows

The present study aimed to evaluate whether the induction and the formation of an accessory corpus luteum (CL) after AI might increase the pregnancy per AI (P/AI) in heat stressed dairy cows. Starting at d 50±3 post-partum, 113 lactating Holstein cows from one commercial herd during summer were scored for body condition, blood sampled and examined by ultrasound. Those bearing a CL>25mm and progesterone (P4) level>2ng/mL were synchronized using a double PGF2α injection given 12 h apart and AI-ed at detected estrus. In total 18 cows, there were not any signs of estrus (n=10) nor a P4 level 0.05). In conclusion, the induction of an accessory CL at d 5 after AI might increase P/AI in heat stressed dairy cows.