OBSERVATIONS ON THE FEMALE REPRODUCTIVE CYCLE OF CAPTIVE ROYAL PYTHONS (Python regius) USING ULTRASOUND IMAGING

Scope of work - The aim of the present study is to monitor the reproductive cycle of female Royal python using ultrasonography. The Royal (Ball) python is one of the most commonly species bred in captivity. To have healthy, well acclimated, captivebred snakes an accurate monitoring of the reproductive activity is necessary. Ultrasonography has been used successfully to evaluate reproduction in many reptile species, such as tortoises, lizards and snakes. Ultrasound indeed allows the visualization of follicles, embryonic structures and viability. Materials and methods - A total of 25 adult female Python regius were examined at one week intervals between January 2015 and January 2016. All the animals were captive born and fed a diet of commercially raised rats. Pythons were individually housed in rack (80x60x20 cm) manteined at temperature of 28-29°C under a 12:12 h L/D cycle. We performed brief (5 min) scans on non-anaesthetized P. Regius using a portable ultrasound system and a 7.5-MHz linear array transducer (Esaote MyLab™ ClassC®). A layer of conductive gel was applied to the snake’s body and the transducer transversely oriented; a series of ventral and lateral scans of the lower third of each individual body was made. The position, ultrasound features, dimension and echogenicity of the ovarian follicles were determined. Results - Follicles in different stages of development were located laterally on both sides within the caudal half of the body in all female samples. We noticed a better view on the right side for nearly all animals. Round, anechoic pre-vitellogenic follicles, homogenous, hypoechoic to hyperechoic vitellogenic follicles, follicles undergoing regression and eggs in varying degrees of calcification were observed. On the basis of the sonographic appearance and size of follicles, we have divided the reproductive cycle in four phases: anovulatory phase (follicles less than 5 mm), transition phase (follicles from 5 to 10 mm), folliculogenesis (follicles from 10 to 30-35 mm) and embryogenesis (embryonic development until deposition). The folliculogenesis ends with ovulation, and thus indicates the correct time for entering of the male. Conclusions- Ultrasonography is a useful non-invasive technique to monitor reproduction both in mammals and in reptiles. The application of ultrasound in snakes has several technical considerations. The scales can produce artifacts due to the thickness of these structures and the potential air trapped between the scales themselves. These problems can be minimized by application of a conductive gel to improve contact with the transducer and displace air from under the scales. Although radiography can be used in reptiles to evaluate mineralized structured, like shelled eggs, there is poor delineation of other reproductive structures in the coelomic cavity. Ultrasonography has been widely used as a rapid and non-invasive method for image soft tissues of the coelomic cavity in reptiles. As regards snakes, there seems to be variability between species. In adult female Boa constrictor, reproductive structures have not been highlighted by ultrasonography. On the contrary, the ultrasound imaging it has been a useful method for the evaluation of reproductive activity in adult female Asian reticulated pythons. The present study suggests that by ultrasound it is possible to clearly identify the different phases of the Royal python female reproductive cycle. It is an important technique for breeding, to precisely detect folliculogenesis phase and thus to highlight the right time to introduce the male. This technique is also useful to identify the females with follicular regression or slugs producing. In conclusion our study suggests that ultrasonography gives an accurate picture of ovarian activity in adult female Royal python.