Response to GnRH Administration at Artificial Insemination in Crossbred Temperate Dairy Cattle Super-ovulated for Embryo Transfer Program under a Tropical Environment

Multiple ovulation and embryo transfer (MOET) technologies are efficient strategies for multiplying high genetic merit cows. Gonadotrophin releasing hormone (GnRH) plays a key role in the endocrine control of ovulations in cattle. The objective of this study was to assess the effectiveness of exogenous GnRH injections at the time of artificial insemination (AI) in super-ovulated crossbred temperate dairy cows under tropical environments. Super-ovulations (n = 24) were conducted using 12 genetically sound dairy cows with a standard protocol with two AIs in a 12-hour interval. Cows in the treatment group (TG) (n = 12) received GnRH (100µg) at the first AI and cows in the control group (CG) (n = 12) did not. Embryos were collected by the non-surgical retrograde flushing technique on day 7 post-AI. Collected embryos were classified according to the standard FAO guidelines. Ovulation rate, embryo recovery rate, percentage of transferable embryos, and rate of degenerated oocytes were compared between the two groups. The ovulation rate (P = 0.083) tended to be higher while the median numbers of embryos recovered (P = 0.003), embryo recovery rate (P = 0.008), and percentage of transferable embryos (P = 0.019) were significantly higher in the TG. Further, the number of degenerated oocytes was notably lower in the same group. The results of the study revealed that the administration of GnRH at the time of AI in superovulation protocols significantly improved the embryo production, recovery, and the number of transferable embryos in crossbred cows in tropical environments.