The Effect of Reduced GnRH Dose on Ovulation and Follicular Dynamics in Ovsynch Programme of Pure and Bunaji-Crossbred Cows

Our objective was to compare the efficacy of reducing GnRH dose from 100 mu g to 50 mu g on the formation of ovulation and sizes of ovarian structures following Ovsynch in apparently healthy Bunaji and Friesian x Bunaji Cows. Thirty female multiparous-apparently-healthy adult [Bunaji (n = 15) and Friesian x Bunaji (n = 15)] breeds of cattle were used. Five cows each were allocated randomly to three groups [control; full dose (FD), and half dose (HD)]. Cows in the control group were treated with 2 ml normal saline while FD-group received 100 mu g lecirelin on day 0, with 500 mu g clorprostenol on day 7 and with 100 mu g lecirelin two days later. Furthermore, HD-group received the same treatment as FD-cows but the dose of lecirelin was reduced to 50 mu g at both times of GnRH administration. Ovarian structures were monitored by ultrasound with a 5-MHZ linear transrectal probe on days - 1 to 12. The ovarian responses of the various groups to first GnRH administration showed (0%, 40% and 60%) ovulation rate for C, HD and FD groups respectively in Bunaji breeds while in Friesian x Bunaji, it was (0%, 60%, 60%). Following second GnRH administration ovulation rate for Bunaji was (20%, 60%, and 60%) for Control, HD and FD-groups, respectively, while for Friesian x Bunaji cows it was (20%, 60%, and 80%). There was no significant difference (p > 0.05) in the days of new follicular wave emergence following the first GnRH administration. It was concluded that 50 mu g Lecirelin reduced the cost of drug without affecting the efficiency of Ovsynch protocol.