Summary. Spirals were inserted by surgery into one or both uterine horns. Ovulation occurred normally at subsequent oestrous periods, but ova were uncleaved at 3 days after oestrus. Spermatozoa were not found at 4 to 24 hr after mating in either oviduct of ewes with a spiral in only one uterine horn. Fertilized ova and spermatozoa were recovered from oviducts of control ewes.
An intra-uterine device in the ewe inhibits sperm transport and ovum fertiliza¬ tion, apparently by causing a reversal in the direction of uterine contractions (Hawk, 1965(Hawk, , 1967 Brinsfield & Hawk, 1969;Mann, 1969). These effects were found weeks or months after the devices had been inserted. Three experiments were designed to determine whether an IUD inserted during oestrus could alter the normal operation of sperm transport mechanisms within a few hours. An additional experiment was designed to determine whether sperm transport would return to normal within a few hr after an IUD was removed.Each IUD was a plastic spiral made from polyethylene rods, as described previously (Hawk, 1967
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