Plastic spirals were surgically inserted into one uterine horn of thirty-two ewes and into both uterine horns of four salpingectomized ewes on Days 4 and 6 of the oestrous cycle, respectively (1st day of oestrus = Day 1). Sham operations were performed on controls. Ewes were autopsied on Day 8 of a subsequent oestrous cycle. The presence of a plastic spiral either in the anterior or posterior portion of the uterine horn interfered with development of the corpus luteum (cl) in the adjacent but

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... t of that in the opposite ovary. The administration of 1600 i.u. of hcg/day from Days 3 to 6 of the oestrous cycle counteracted the inhibitory effect of the spiral on cl development. Intra-uterine spirals interfered with cl development in salpingectomized ewes, thus eliminating the oviduct as a major pathway through which the inhibitory effect of the spiral on thecl is mediated. The oestrous cycle during which spirals were inserted was not consistently shortened when the cl were present only in the ovary adjacent to the operated uterine horn.