STUDIES ON THE PLACENTA OF THE SHEEP (OVIS ARIES L.)

Abstract

Various numbers of caruncles, up to eighty-four, were removed surgically from forty-two Merino ewes before mating. Fertility was not apparently related to the number of caruncles removed except that pregnancy terminated some weeks prematurely in some of the ewes in which sixty or more caruncles were removed. Birth weight was reduced by removal of caruncles, but was more closely correlated with the weight of functional cotyledons than with their number. Reduction in the number of caruncles was partly compensated for by an increase in weight of individual cotyledons. This compensation was proportionately greater in foetal than in maternal tissues. There was no clear evidence of the formation of new caruncles but there was evidence that the number of caruncles may decline spontaneously. It is concluded, that, while very little placental tissue is necessary to allow gestation to reach the 100th day, when foetal weight begins to increase rapidly, subsequent foetal growth is limited by the size of the placenta. The results also show that estimation of foetal age from physical dimensions of the foetus may be grossly misleading.