Synchronizing follicle growth in cattle.1
Keywords: synchronize, bovine, ovsync, cow
Image size: 5370 x 3534px
This diagram, extrapolated from many sources, shows the receptive periods during the estrous cycle when GnRH will cause ovulation (gray vertical bars). If GnRH is given during any of these periods, 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.
Seven days after the initial injection of GnRH, an injection of prostaglandin is given to cause luteolysis of the corpora lutea that were formed seven days earlier. Two days later the injection of prostaglandin, other injection of GnRH is given so that the follicles that have grown in the new wave are induced to ovulate. Sometimes cattle are bred at this time; this is called "Cosync" treatment because the second injection and the time the breeding coincide. Alternatively, they can be bred at a fixed time, usually about the morning after the second injection of GnRH (about 16 hours later). This is referred to as "Ovsync" because ovulations are closely grouped around this period of time. Finally, cows may only be selected for breeding if they show heat; hence the name "Selectsync".
In some instances, injections of prostaglandin are given (even of "Ovsync" itself may be used) to increase the chances that cows will be in the receptive periods (gray vertical bars) at the time the first GnRH is given for Ovsync. The economic value of these pre-synchronization ("Presync") treatments is questionable.
