Revisiting "preovulatory follicular stasis" in reptiles

Failure of oviposition in reptiles is either based on a pre- or postovulatory condition. Although postovulatory dystocia is easier to diagnose and treat, and undoubtedly pathological, the pathophysiology of failure of ovulation is poorly understood. The common perception is that of a static condition, a “follicular stasis,” and ovariectomy is the commonly recommended treatment. Unovulated follicles undergo a resorptive process. It is important to distinguish between follicular atresia (FA) and follicular regression (FR). FA is the selecting force on individual follicles during follicular development, a common and physiological process in all vertebrate species for limiting clutch and litter size. FR is the process of “follicular stasis,” the elimination of entire batches of late mature follicles in nonmammalian species. The etiology of FR is likely multifactorial, but there is evidence for a physiological, adaptive process to environmental or social conditions, observed not only in captivity but also in natural habitats. Although the complete resorption may take several months and some forms (in particular, cystic atresia) may be mistaken for a pathological condition, FR is neither a static nor a pathological process per se. It is, however, undisputed that some affected reptiles suffer from the consequences of accumulated unovulated follicles, including yolk coelomitis, metabolic derangements, and mechanical impacts of the coelomic mass effect. In addition, the endocrinological impact of corpora atretica (whitening bodies) on the ovulation of future batches of follicles and the welfare of affected animals remain unknown. Although ovariectomy may in fact be the best option for a companion pet reptile, premature interventions and loss of reproductive potential are detrimental for the sustainability of conservation breeding programs. Acknowledging the continuous resorptive and physiological nature of FR, monitoring and allowing enough time for follicular resorption, and performing partial ovariectomy are recommended for female reptiles in breeding situations.