The direction of uterine contractions in vivo was studied in oestrous ewes by recording the motility of exteriorized uteri on cine film. In eight control ewes, 58% of 1156 contractions moved towards the oviduct, while 16% moved towards the cervix. In eight ewes with a plastic spiral in the lumen of one horn, only 17% of 927 contractions moved towards the oviduct; 70% of the contractions moved towards the cervix. The effect of the IUD on the direction of uterine contractions may explain inhibition of sperm transport and ovum fertilization in `IUD' ewes.
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