The effect of pregnant mare serum gonadotrophin and human chorionic gonadotrophin on ovulation and on fertility in the ewe

Abstract

An experiment involving 300 cyclic Merino ewes and designed to study the effects of pregnant mare serum gonadotrophin (PMSG) and human chorionic gonadotrophin (HCG) on ovulation and subsequent fertility is described. PMSG (750 i.u.) was given on the 12th day of the oestrous cycle and HCG (400 and 800 i.u.) was injected intravenously within 3 hr of the onset of oestrus. PMSG induced multiple ovulation and hastened the time of ovulation in relation to the onset of oestrus by 2-3 hr, but did not enhance the precision of the time of ovulation. HCG had no effect upon the time of ovulation but did increase the proportion of follicles which ruptured. Neither PMSG nor HCG, alone or in combination, adversely affected fertility. In fact, HCG increased the proportion of ewes which lambed. Both PMSG and HCG increased the incidence of multiple births. The effect of PMSG on the incidence of multiple births was a direct reflection of its ability to induce multiple ovulation. HCG given alone, or after PMSG increased the incidence of multiple births but its effect was less marked than that of PMSG, and unlike that of PMSG the effect of HCG did not appear to be solely due to an increase in the number of ovulations.