Ovulation Rates of Beef Cows and Heifers Treated with Equine Gonadotropin (PMS) and Chorionic Gonadotropin (HCG)

Abstract

It has been demonstrated that the induction of multiple births in cattle can be accomplished by the injection of PMS (Gordon, Williams and Edwards, 1962; Turman, Renbarger and Stephens, 1968). These workers and others have reported that prenatal and postnatal mortality is less in twin than in higher multiple pregnancies and births. Therefore, the determination of a sequence of gonadotropin injections that will result in a high percentage of two ovulations is one of the requirements for developing a practical program for the induction of multiple births. In addition, the need to time the gonadotropin injections rather precisely during the estrous cycle (Casida et al., 1943; Willett, McShan and Meyer, 1952), plus a consideration of labor requirements suggest that such a program should also include estrous synchronization. The objective of this study was to determine a sequence of PMS and HCG injections, timed from either a natural or synchronized estrus, that would give a high percentage of two ovulations in beef cows and heifers.