The effect of using GnRH or eCG, 6 days before the implementation of the Ovsynch protocol on the ovarian rebound and pregnancy rate of anestrus dairy cows in the early postpartum period
Fertility in the postpartum period in cows is negatively affected by the prevalence of inactive ovaries. The aim of the recent study was to evaluate the effects of administration of 250 µg GnRH or 750 IU eCG before the implementation of Ovsynch protocol on pregnancy rate and reproductive parameters of dairy anestrus cows. The studied cows with an average of 61.1 ± 0.08 days in milk (DIM) at the 1st post partum inseminatoin were randomly assigned to one of the following treatment protocols and received the following treatments: Ovsynch (GnRH-7d-PGF2α-56h-GnRH(GnRH2)-18h-Fixed time artificial insemination(FTAI), n=87), GnRH-Ovsynch (250 µg GnRH-6d-Ovsynch, n=85), and eCG-Ovsynch (750 IU eCG-6d-Ovsynch, n=88). The pregnancy diagnosis tests were done 30-32 days after AIs by ultrasonography. Non pregnant cows were repeatedly treated with the same protocol in their groups. The period of the study lasted until day 168 after the beginning of the experiment. The eCG-Ovsynch protocol significantly increased the ovulation rate at GnRH2 compared to the Ovsynch protocol (p=0.03). The GnRH-Ovsynch and eCG-Ovsynch protocols significantly reduced the interval between treatment and pregnancy compared to the Ovsynch protocol (p=0.04 and p=0.02, respectively). The eCG-Ovsynch protocol increased the pregnancy rate of cows at the 1st postpartum insemination compared to the Ovsynch protocol (p=0.02). For cows that were inseminated ≤60 days postpartum, there was a statistically significant difference between the pregnancy rates of cows receiving the eCG-Ovsynch compared to the cows receiving the Ovsynch protocol (p=0.03). A similar result was achieved for cows that were inseminated >60 days post partum between eCG-Ovsynch and Ovsynch protocols (p=0.02). For GnRH-Ovsynch protocol, there was a statistically significant difference between the pregnancy rate of cows with a DIM<60 compared to the cows with a DIM>60 at the 1st post partum AI (p=0.03). A similar result was achieved in the eCG-Ovsynch protocol (p=0.05). Implementation of the eCG-Ovsynch and GnRH-Ovsynch protocols significantly reduced the interval between treatment and pregnancy compared to the Ovsynch protocol. Implementation of the eCG-Ovsynch protocol increased the pregnancy rate of cows at the 1st postpartum insemination compared to the Ovsynch protocol.