A radiographic study of the fetus in late pregnancy and during foaling.

The position, posture and presentation of the fetus were studied by serial radiography of the abdomen in 18 crossbred Pony mares near term and during first- and second-stage labour. In 3 mares the fetal position was assessed before and after induction of parturition with the synthetic prostaglandin, fluprostenol. In late gestation and up to the time of first-stage labour the fetus lay in ventral position with the forelimbs and poll flexed or partly flexed. At this time fetal movements were confined to flexion and extension of neck and forelimbs, but at parturition the head and limbs gradually extended the the forelimbs, head and neck rotated so that dorsal position and cranial extension were achieved. From this position, with the forelimbs and muzzle engaged in the cervical canal, delivery was quickly effected. The trunk and hindlimbs came into dorsal position during second-stage labour. The mechanics of these fetal movements and their relation to causes of dystocia are discussed.