Distribution of spermatozoa in the mare's oviduct.

The morphology of the uterotubal junction (UTJ) and caudal isthmus during the peri-ovulatory period, and the distribution of spermatozoa within the region, were studied in 10 Pony mares. The proximal tip of the uterine horn and caudal 1-2 cm of the isthmus were removed during oestrus or shortly after ovulation from animals mated or artificially inseminated within the previous 24 h. The tissues were incised longitudinally and fixed for scanning electron microscopy. Analysis of micrographs showed deep longitudinal and oedematous folds in the preovulatory samples. After ovulation, much of the folding and oedema disappeared. There was a regional arrangement of ciliated and nonciliated cells and the cilia showed evidence of directional orientation. Occasional spermatozoa were seen in some specimens deep in furrows between folds of the UTJ.