Accurate monitoring of reproductive activity is necessary for success of captive breeding and recovery of endangered species. Using ultrasonography, we aimed to describe the stages of follicle development of the endangered Louisiana pinesnake (Pituophis ruthveni). Ultrasound procedures were performed weekly for 11 females during the 2020 reproductive season by submerging the last half of an unanesthetized female in water and using a 3.0-10.0 MHz linear array transducer placed and moved along the gastrosteges to explore the whole reproductive tract. The presence of follicles, their size, echogenicity, and stage of development was assessed. We observed small, round, anechoic, linearly aligned previtellogenic follicles in the coelom at the beginning of the reproductive season and found that structures dramatically increased in size and shifted in echogenicity as follicles matured and developed before and after ovulation. We classified follicles according to ultrasonographic appearance into 7 different follicle categories: previtellogenic, early vitellogenic, vitellogenic, preovulatory, peri-ovulatory, post ovulatory, and shelled. Using ultrasound, we developed markers of progressive follicular maturation for the Louisiana pinesnake and identified signs of abnormal development and post ovulatory follicle reabsorption. Detailed description of follicular maturation will be useful to improve captive breeding successes, identify mechanisms of reproductive failure, and develop artificial insemination.
Keywords: anatomy; captive breeding; conservation; endangered species; follicles; oviduct; reptile; ultrasonography.