THE EFFECT OF A SUSTAINED-RELEASE INJECTION OF HUMAN CHORIONIC-GONADOTROPIN ON CORPUS-LUTEUM FORMATION AND PROGESTERONE SECRETION IN BEEF HEIFERS

A sustained-release injection of human chorionic gonadotropin (HCG) wa s administered to Syncro-Mate B(R) synchronized beef heifers 12 hours after estrus. The sustained-release formulation doubled the ovulation rate, increased corpora lutea size, increased the incidence of cystic corpora lutea, and tended to increase progesterone concentrations. Sus tained release of HCG produced effects similar to larger doses and/or multiple aqueous injections of HCG. The doubling of multiple ovulation s may have been a result of availability of persistent follicles cause d by the Syncro-Mate B(R). The increase in corpora lutea size was part ially caused by the more frequent presence of fluid-filled cavities wi thin the corpora lutea (cystic corpora lutea). In summary, the sustain ed-release injection of HCG accomplished similar effects as larger dos es and/or multiple administrations of nonsustained-release formulation s of HCG.