Prostaglandin F2 alpha for oestrus synchronisation or abortion in Polwarth ewes

Each of 411 Polwarth ewes was given prostaglandin (125 micrograms cloprostenol) by injection on 2 occasions 10 days apart. Ewes were not mated at either prostaglandin induced oestrus, but field mated at the first natural oestrus thereafter. As a result 97.1% mated in a 12 day period (82% in 4 days). From a selected group of 270 ewes, presumed to have been pregnant (by non-return to sevice), 90 were given prostaglandin (125 micrograms cloprostenol) as an abortifacient, at 22-23 days post service, the remaining 180 acting as lambing controls. Pregnancy was finally determined by ultrasonic fetometer at 106-107 days post mating. A 100% accuracy was achieved being confirmed by lambing observations. Most (98.9%) of the control, as expected, proved to be pregnant and subsequently lambed. By contrast only 33 (36.7%) of the prostaglandin treated ewes were pregnant. Thus, although prostaglandin aborted 63.3% of pregnant ewes, its efficacy was much less than might have been expected. The authors then discuss the efficacy of prostaglandin as an abortifacient at various stages of gestation.