Hormonal responses to GnRH injection given at different stages of the estrous cycle in water buffaloes

The objective of the present study was to evaluate the hormonal responses of buffaloes to GnRH injections given at different moments of the estrous cycle. The estrous cycles of 15 buffaloes were synchronized with 2 im injections of prostaglandin F2a given 11 days apart. The buffalos were randomly assigned to 1 of 3 groups. Buffaloes in the control group received no treatment, whereas GnRH6 buffaloes received a GnRH injection between days 5 and 7 and GnRH16 buffaloes received a GnRH injection between days 15 and 17 of the estrous cycle (estrus = day 0). Up to day 6, the plasma progesterone levels in the three groups were low (1 c 0.16 ng/ml) but gradually increased until day 12 (4.62 c 0.41 ng/ml). The amount of plasma progesterone concentrations decreased from day 15 of the estrous cycle in all groups of buffaloes. No significant differences were observed in the plasma level of progesterone and estradiol concentrations of the three groups during the estrous cycle. The peak levels of plasma estradiol were observed on day 20 and the differences were not significant (11.34 c 1.77, 11.74 c 1.91 and 12.72 c 2.49 pg/ml in the control, GnRH6 and GnRH16 groups, respectively (P> 0.05). In conclusion, GnRH given at the beginning or at the end of the estrous cycle did not alter the profile of progesterone and estradiol concentration in buffaloes.