Effect of Gonadotropin-Releasing Hormone Treatment on Superovulation Response and Embryo Recovery in Holstein Heifers: A Field Trial at Zagros Milk and Meat Company, Iran

Background: Superovulation is a crucial component of assisted reproductive technology. Inducing superovulation with Gonadotropin-releasing hormone (GnRH) can lead to ovarian hyperstimulation, potentially affecting reproductive outcomes. Objectives: This study aimed to examine the effects of GnRH treatment on superovulation response and embryo recovery in Holstein heifers. Methods: Twenty-one Holstein heifers (age: 135.15 months; weight: 361.05 kg) were selected based on their general health status and ovarian function. All heifers received two consecutive doses of prostaglandin F2α and underwent superovulation. The heifers were inseminated twice: Once at the onset of standing estrus and again 12 hours later. In the treatment group (13 heifers), a single dose of GnRH was administered simultaneously with the second insemination. The superovulation response was evaluated based on the number of corpus luteum (CL), unovulated follicles (UoF), total recovered embryos/ova, and the number of transferable embryos, using logistic regression with the GENMOD procedure in SAS. Results: The mean number of CL was not significantly greater in the control group (13.6) compared to the GnRH group (11.4). The average number of UoF was similar between the two groups (P = 0.1853). However, the control group had a significantly higher average total number of recovered embryos/ova (7.7) compared to the GnRH group (2.1). Additionally, the control group progesterone more transferable embryos, with an average of 2.5, while the GnRH group averaged 0.7 (P 0.0062). Conclusions: Gonadotropin-releasing hormone likely deactivated the oviduct by disrupting the balance of estradiol and estrogen, leading to a reduction in both the total number of embryos and the number of transferable embryos in heifers.