Effect of three methods of estrus synchronization: Osynch, Co-Synch and Prostaglandin on the fertility of subfertile dairy cows

This study was performed to compare the effect of using 3 different estrus synchronization methods (Ovsynch, Co-Synch and Prostaglandin) on the conception rate of subfertile dairy cows. Fifty one subfertile Holstein dairy cows with parity ranging from 1 to 7 were enrolled in this study. Cows were allocated to three groups Ovsynch (n=10), Co-Synch (n=27) and Prostaglandin (n=14). Cows in the Ovsynch group underwent a standard Ovsynch protocol (GnRH analogue on Day 0, PGF2α analogue on Day 7 and GnRH analogue on Day 9), then they were artificially inseminated approximately 16 hours after the second GnRH treatment. The same procedure was done for cows in Co-Synch group, but artificial insemination took place immediately after the last injection. Cows in prostaglandin group underwent a PG protocol (PGF2α, on Day 0 and 12), and artificial insemination was done about 72 hours after the second PGF2α injection. Pregnancy diagnosis was performed 60 days after insemination via rectal examination. By using logistic procedure of SAS 9.1 software, the effects of treatment, season, parity, animal, age and open days were analyzed. The analysis of variables related to animal and the measured effects on pregnancy proved that none of the evaluated parameters were significant. Hence, we cannot declare which of the estrus synchronization methods is suitable to increase pregnancy rate. Further studies with more replicates are required to choose the best method.