The effect of different preovulatory serum estradiol concentrations on the conception rate of synchronized dairy cattle

Lactating Holstein dairy cows (n = 167) were assigned randomly to four treatments groups. two groups presynchronized with two injection of PGF2α, 14 days apart and then followed with Ovsynch and Heatsynch (presynch-ovsynch or presynch-heatsynch) and two other groups presynchronized with one injection of PGF2α and two day after that receive GnRH 6 d before the first GnRH injection of ovsynch and heatsynch (G6G-ovsynch or G6G-heatsynch). Four blood samples were collected from cows for determination of plasma progesterone concentration. Sample 1 and 2 for determining the cyclic cows and Third samples 24h after PGF of the Ovsynch and Heatsynch protocol were taken to assay blood serum estradiol. The fourth sample was taken at 21 days afetr AI. Transrectal ultrasonography was performed to diagnose pregnant cows 30 d after AI. Mean milk production and BCS around AI time was similar among treatments. Estradiol concentration at proestrus was similar among groups. Although conception rate was higher in Presynch-Heasynch (%53 versus %43 in presynch-ovsynch and G Gheatsynch and %39 in presynch-ovsynch) but this difference was not significance. There was a significance positive correlation between estradiol conentration and conception rate 0.267) in our study in total but this correlation was higher in G6G-Ovsynch (0.343). This study has shown that there is a positive corrolation between preovulatory estradiol concentation and conception rate in the synchronized dairy cattle.