Evaluation of the Follicular Cycle in Ball Pythons (Python regius)
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.Abstract
Long axis, ventrolateral approach of the cranial third of the abdomen. (A) A 3 mm nonvitellogenic follicle that seems mostly anechoic; however, there is no evidence of distal acoustic enhancement that would indicate a fluid composition. (B) Adjacent blood vessel that can be mistaken for follicles, when viewed in cross section. (C) Rib and its associated distal acoustic shadowing. That artifact may create false follicles or impair the visualization of underlying follicles.
Long axis, lateral approach of the cranial third of the abdomen. (A) A 7 mm round, vitellogenic follicle with a thin hyperechoic rim. (B) Anechoic center of the follicle. (C) These follicles are often found in short chains with other follicles as demonstrated with this adjacent follicle.
Long axis, ventrolateral approach of the mid abdomen. (A) A 12.6 mm follicle undergoing vitellogenesis. (B) Vitellogenesis is represented by the echogenic material consisting of calcium, lipids, and phosphoproteins developing within the rim of the follicle. (C) A shrinking anechoic center of the follicle is seen as vitellogenesis progresses.
Long axis, ventrolateral approach of the mid abdomen. (A) Two 20 mm vitellogenic follicles. (B) Anechoic free fluid between the two follicles with evidence of mild distal acoustic enhancement. (C) An alternating hypoechoic and hyperechoic outer rim is observed with follicles of this size.
Long axis, ventrolateral approach of the mid abdomen. (A) A 26 mm follicle consistent with a post ovulatory follicle. Note the elliptical rather than circular shape. (B) The hypoechoic outer rim. (C) The thin hyperechoic inner rim.
Long axis, ventrolateral approach of the mid abdomen. (A) A 42 mm follicle. Note the increasing elongated elliptical shape with no apparent shell deposition. (B) The contents of the follicle are similar to a soft tissue echogenicity. (C) An anechoic center develops within the follicle before eggshell deposition. (D) Note the rib shadowing, a commonly encountered artifact.
Long axis, ventrolateral approach of the mid abdomen. (A) A hyperechoic rim representing eggshell deposition is seen surrounding the follicle. Observe how the eggshell mineralization is occurring and its associated distal acoustic shadowing results in an overall darker appearance.
Long axis, ventrolateral approach of the caudal abdomen. (A) A hyperechoic structure thought to possibly be a corpus luteum. The structure is irregularly rounded and is slightly smaller than the neighboring follicles. (B) Neighboring follicles. Note the ribs and their associated distal acoustic shadowing.
Follicular quiescence. The follicles undergo follicular waves of growth and regression, but never exceeded 10 mm in size.
Follicular atresia. The follicles develop to be larger than 10 mm in diameter but growth becomes static before reaching 20 mm. Follicular atresia occurs after 50 or more days of ovulatory stasis.
Follicular maturation. The follicles develop slowly, but once they reach approximately 20 mm they begin a more rapid increase in size. This pattern of follicular development is similar between each individual.
