This study evaluated the development of ovarian follicles of ball pythons (Python regius) ultrasonographically over two breeding seasons. In the first breeding season, four mature, adult female ball pythons were examined at 4–6 wk intervals. Data collected during each examination included the snake's weight and the number and size of the follicles observed. Dominant follicles were counted as “large” follicles and differentiated from the “small” follicles at a diameter of 20 mm. Snake behavior was observed daily. Three mature females ovulated and produced eggs during this season, whereas the fourth resorbed all follicles. In the second breeding season, four nulliparous females were added to the original four mature adults. They were examined ultrasonographically at 2–4 wk intervals, with similar data collected during each examination. The data from these two breeding cycles suggest that there are three distinct, identifiable stages of follicular development: follicular quiescence, atresia, and development to oviposition. Distinct morphological changes during follicular growth and maturation can be clearly observed ultrasonographically. As dominant follicles emerge, reliable predictions of ovulation dates, viable eggs, and number of eggs are possible. This study also provided data to predict ovulation dates and the expected number of eggs in ball python clutches.

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