Effect of Utilization of Single or Double Prostaglandin Administration Within an Ovsynch Fixed-Time Artificial Insemination Protocol During Summer Season in Dairy Cows

This study investigated the fertility of dairy cows during summer season after treatment with a single or double PGF_2α in a progesterone (P4)-based Ovsynch protocol for fixed-time artificial insemination (FTAI). The data were compared to a treatment effectuated during winter season. Two groups of 60 dairy cows each were randomly assigned on day 60 post-partum to single PGF_2α or double PGF_2α group. At removal of the P4 treatment the single PGF_2α group received a single dose and the double PGF_2α group received two doses of PGF_2α at 24 hours apart. In each group, 30 cows were treated during the summer (June, July and August) and 30 cows during the winter (December, January and February) season. During summer season a double PGF_2α dose did not influence pregnancy rate at FTAI but improved cumulative pregnancy rate 60 days after FTAI (43% vs 69% for single PGF_2α and double PGF_2α administration, respectively; P<0.05). During winter season the single or double PGF_2α administration did not modify PR or cumulative PR. In conclusion, during summer the utilization of a double instead of single PGF_2α treatment into a P4-based Ovsynch-FTAI protocol did not increase pregnancy rate at FTAI but improved cumulative pregnancy rate.