Clinical Exposures: Preovulatory stasis and dystocia in oviparous lizards - Veterinary Medicine
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Clinical Exposures: Preovulatory stasis and dystocia in oviparous lizards


Reproductive disorders are common in captive reptiles (lizards, chelonians [tortoises, turtles], and snakes).3 The most common reproductive disorders in female reptiles are preovulatory follicular stasis and postovulatory egg stasis (dystocia), which are often related to inappropriate husbandry (malnutrition, an inadequate nesting site, inappropriate temperature and humidity, or the absence of a UVA and UVB source).1 Sexual maturity in reptiles is determined predominantly by body size, though age plays a secondary role. In captivity, reptiles can reach sexual maturity much earlier than in natural environments,1 so preovulatory stasis may be seen in relatively young (< 1 year old) captive reptiles. The presence of a male in the same terrarium does not affect the incidence of preovulatory stasis. Preovulatory stasis is not seen in wild lizards.

Normal follicular development in reptiles

An important phase in follicle development in reptiles is vitellogenesis (i.e. formation of yolk in the liver, with subsequent deposition around the ova within each follicle).4 Estrogens stimulate the liver to convert the adipose tissue and dietary lipids into vitellogenin,4 which is selectively absorbed from the circulation by the follicles. During this stage, follicles can reach up to 100 times their original size. The liver also dramatically enlarges and becomes bright yellow.

Large amounts of calcium, essential for shell formation, are also added to the follicles. During this phase, total serum calcium concentrations are as much as two to four times higher than normal.5 Most of the serum calcium is bound to serum proteins, including vitellogenins and egg yolk lipoproteins. Ionized calcium may also increase slightly.

The follicle becomes an egg after the deposition of albumin and formation of a shell inside the oviduct. After ovulation, there is little exchange of nutrients between the female and the egg.

Causes of preovulatory stasis and dystocia in reptiles

An interruption in follicular development can result in preovulatory stasis. The cause of preovulatory stasis is often difficult to determine, though a husbandry-related problem is most common. For example, if the animal lacks exposure to UVB rays and has inadequate calcium supplementation,3 it may not be able to complete ova development and subsequently cannot ovulate. Large amounts of calcium in the yolk serve the neonatal lizard's needs,4 and calcium is necessary for shell development. In this case, the cause of the condition could not be determined.

3. A dorsoventral radiograph of a green iguana with numerous shelled eggs in the abdomen. Note that the shelled eggs are more radiopaque, with more distinct outlines, than the nonshelled follicles shown in Figure 1.
Dystocia occurs when the animal ovulates and develops eggs (Figure 3) but is unable to pass them from the oviduct. This condition may arise because of a problem with the egg itself (malpositioning, malformation, or rupture) or a problem with the female such as a pelvic or oviductal malformation or masses not related to the reproductive tract such as abscesses or urinary bladder calculi.3 A female that has had a previous dystocia is predisposed to having it occur again as a result of scar tissue from previous salpingotomies.6 Other causes include poor physical condition (captive reptiles may not have the muscle tone needed to lay their eggs), dehydration, low environmental temperatures, low humidity, and the lack of a suitable area for nest digging.3 Although oviductal infection is a potential cause, infectious etiologies are not well-documented or well-understood in reptiles.


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