Evaluation of the Effects of GnRH and hCG Administrations during and after Insemination on Fertility Parameters of Dairy Cows

Background: Getting pregnant and maintenance of the pregnancy in cows is crucial for the dairy farmers for sustainable production. Many methods are used for this purpose, one of them is the administration of gonadotropins at insemination and later in the early embryonic period. In this study, it was aimed to investigate the effects of different gonadotropin applications on fertility. Methods: A total of 406 dairy cows were divided randomly into five treatment groups according to GnRH (10 µg buserelin acetate, im) and hCG (1500 IU, im) administrations in different time periods at AI and post AI as; GI (n=84, d7; hCG), GII (n=106, d7; GnRH), GIII (n=62, d0 and d7; hCG), GIV (n=80, d0 and d7; GnRH), GV (n=74, d0 and d7; placebo: 2.5 ml 0.9% NaCl). Pregnancy control was done on day 30 and 45 post AI. Fertility parameters (conception rate, first service pregnancy rate, pregnancy per AI, embryonic loss) were calculated with the obtained data. Result: Our findings indicated that double dose hCG administration caused an improvement on the fertility parameters in cows with greater than 150 DIM. Also, conception rates of the cows with higher parity, milk yield and lower BCS improved with the administration of hCG on d0 and d7. We concluded that double-dose hCG administrations on d0 and d7 can be used to improve fertility after 150 DIM in cows with higher parity and milk yield.