Experimental control of fertility has been accomplished by inserting foreign objects in the uterus. Doyle & Margolis (1963) found that a suture in the uterine lumen of the rat prevented implantation of blastocysts. This was soon followed by similar studies on the rabbit (Adams & Eckstein, 1964), cow (Hawk, Conley, Brinsfield & Righter, 1965) and ewe (Hawk, 1965) . A local inhibitory effect on luteal function has been demonstrated by inserting plastic coils in an anterior portion of a uterine

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... n in the ewe (Ginther, Pope & Casida, 1966) and heifer (Ginther, Woody, Janakiraman & Casida, 1966). Uterine distention does not alter oestrous cycles in the pig (Anderson, 1962); however, a local uterine luteolytic effect has been observed during pregnancy (du Buisson, 1961). This investigation concerns the effect of an intra-uterine foreign body on the occurrence of pregnancy in the pig. The intra-uterine foreign body (IUFB) consisted of an open end vinyl tube (2\m=.\23 mm O.D., Clay-Adams, Inc.), which was silicone-treated and sterilized. It was inserted into one uterine horn of the pig during the luteal phase (Days 8 to 12) of the oestrous cycle. Under halothane-oxygen anaesthesia, incisions (1 to 2 cm length) were made in the uterine wall about 10 cm posterior to the utero-tubal junction and either in the mid-portion or about 5 cm from the bifurcation of the horns. The IUFB (50 to 60 or 100 to 120 cm in length) was inserted into the uterine lumen, either into the anterior half (five animals) or into the entire horn (five animals). It was attached at each end by a loose loop of nylon (size 3). Both incisions were closed with silk (size 4-0). Ten pigs were used as unoperated controls. The pigs were checked daily for signs of oestrus and were mated each day of oestrus. Those animals which returned to oestrus after service were mated for a maximum of four post-operative oestrous periods. Oestrous cycles after insertion of IUFB (including cycles of those animals that failed to remain pregnant) were 19-7 + 0-3 days (mean and se) and those of control animals before mating were 19-7 + 0-5 days. Results in the two experimental groups were similar and therefore were combined. There was