Veterinary Medicine - November 2008 - (Page 596)

Clinical Exposures PEER-REVIEWED in this lizard, is not a typical ﬁnding with this condition but may have been caused by estrogen toxicosis, as a result of the high estrogen concentrations associated with follicular growth. While estrogen-induced marrow aplasia has been well-documented in dogs and ferrets,2 this effect has not been reported in reptiles. DISCUSSION 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. 2. Postmortem examination of the coelomic cavity of a female bearded dragon with preovulatory stasis. The liver shows normal fatty change associated with vitellogenesis. Both ovaries contain numerous round, bright-yellow, nonshelled vitellogenic follicles. Part of the small and large intestines, both kidneys (K), and the fat bodies (FB) are also shown. 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 dif- ﬁcult to determine, though a husbandryrelated 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. 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 596 November 2008 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - November 2008

Veterinary Medicine - November 2008 Contents Leading Off Editors' Guest Just Ask the Expert Letters Practice Makes Perfect Clinical Exposures Practice Matters Idea Exchange Author Guidelines A Challenging Case: Esophageal Leiomyoma in a Dog Osteoarthritis in Cats: What We Now Know About Recognition and Treatment Product Preview CE Form/Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - November 2008

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