Synchronizing follicle growth in cattle; Ovsynch
Keywords: synchronize, bovine, ovsync, cow, estrous, estrus, cycle, mechanism
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This diagram, extrapolated from many sources, shows the mechanism of Ovsynch treatment.
The receptive periods during the estrous cycle when GnRH will cause ovulation are shown as gray vertical bars. If GnRH is given during any of these periods (about 65% of the duration of a three wave estrous cycle) follicles present at that time will ovulate, causing a drop in inhibin, FSH release, and the start of new wave of follicle growth. It is this wave of of follicle growth that is utilized to provide synchronous ovulations about nine days later.
As mentioned, a synchronous response to the first injection of GnRH occurs in about 65% of cows. Nine days after the first injection of GnRH, some of the non-responding cows will either respond to the injection of prostaglandin and show estrus or they may show estrus spontaneously. In this manner, about 65% of cows will respond to the first injection of GnRH and about 35% of the cows (the non-responders) will be in estrus after the injection of prostaglandin and will respond to to the second injection of GnRH, together with the other cows. Collectively this means that about 85% of all the treated cows could respond to Ovsynch treatment.
These figures assume that all the cattle being treated are actually having estrous cycles. In high producing cows, is seldom the case so the response to Ovsynch treatments may often fall short of these calculations.
