Lack of effect of melatonin on ovarian function and response to estrous synchronization and fixed-time AI during the nonbreeding season in lactating dairy buffalo (Bubalus bubalis).

The present study was conducted to examine whether pretreatment with melatonin would enhance ovarian follicular functions and increase response to estrous synchronization and fixed-time AI (TAI) during the nonbreeding season in lactating dairy buffalo. In Experiment 1, buffalo cows without a detectable corpus luteum (CL) were assigned on Day -20 (D-20) to three groups: control (n = 12); melatonin (n = 13); progesterone (P4) (n = 15). Cows in the melatonin group were implanted with melatonin on D-20. From D0 to D9, there was imposing of an estrous synchronization treatment regimen using either a standard Ovsynch protocol (control, melatonin) or a P4-based Ovsynch treatment regimen (P4). There were no differences (P > 0.05) among groups for the presence of a CL at D0, size of the largest follicle at D0, ovulation to GnRH injection at D0 and D9, or the time to ovulation after injection of GnRH at D9. In Experiment 2, there was imposing of the same treatment regimens as in Experiment 1, with inclusion of TAI. Females of the P4 group had a greater (P = 0.001) pregnancy/AI percentage (60 %) than those in the control (17 %) and melatonin (23 %) groups. Females of the P4 group also had a larger (P = 0.005) CL at D20 compared with those in the control and melatonin groups. Findings indicate treatment with melatonin for 20 days did not affect ovarian functions or the response to an estrous synchronization treatment regimen and TAI during the nonbreeding season in lactating dairy buffalo.