The Effect of Pregnant Mare Serum Gonadotrophin on Ovulation Rate in Scottish Half-Bred and Scottish Blackface Ewes

Abstract

SUMMARY The effects on ovulation rate of intramuscular or subcutaneous injection of pregnant mare serum gonadotrophin (PMSG), and the timing of this injection in relation to the oestrous cycle, were examined in two experiments with Scottish Half-bred and Scottish Blackface ewes. Oestrus was synchronized with progestagen sponges in all experimental treatment groups with the exception of the group injected on day 13 of the oestrous cycle. PMSG was injected at sponge withdrawal, at the onset of oestrus and 8 hours after the onset of oestrus and on day 13 of the oestrous cycle. Neither the route of administration nor the timing of the injection influenced ovulation rate. Ovulation rate was highest with 1500 i.u. PMSG and 1000 i.u. PMSG in the Scottish Half-bred and Scottish Blackface respectively. There was a suggestion that conception rate at the first post-treatment oestrus was reduced by progestagen treatment.