Today's Veterinary Practice

NOV-DEC 2018

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68 NOVEMBER/DECEMBER 2018 todaysveterinarypractice.com PEER REVIEWED REVIEWED PEER Hypervitaminosis A is a nutritional disorder, an overload of vitamin A, which in reptiles can be iatrogenically induced by injection of vitamin A to reptiles suspected of having hypovitaminosis A. 1-3 Vitamin A is a fat-soluble vitamin, meaning that it dissolves in fats and oils, and is a major part of commercially prepared diets. Vitamin A supplements are often given presumptively to reptiles because hypovitaminosis A is a known nutritional problem that often results from unbalanced diets. 2,4 The safe dose for vitamin A administration is 5000- 10,000 IU/kg, and a toxic dose is roughly 100 times higher (50,000 to 100,000 IU/kg). 1,2 The risk for overdosing can be decreased by administering vitamin A in an oral, rather than injectable, formulation. 3 However, hypervitaminosis A can still be induced, even when a "safe dose" of supplement is given as an injection and an increased amount of vitamin A is consumed as part of the diet for a prolonged period. 2 Vitamin A plays an important role in maintaining normal epithelial tissues and is vital for vision, growth, reproduction, and immune function; it is stored in the liver. 2 Excess levels of vitamin A (i.e., toxicity) overwhelm the hepatic function and storage capabilities and lead to tissue damage, which then is clinically seen initially as dry, flaky skin. 1,4 Herbivorous reptiles typically do not experience vitamin A deficiency because of their plant-based diet and their ability to synthesize vitamin A. 1,2 Plants, which contain vitamin A precursors called carotenoids (beta-carotene, lutein, and canthaxanthin are the most essential), include leafy greens, orange and yellow vegetables, and fruits. 2 However, some reptiles, such as carnivorous turtles and other carnivorous reptiles (e.g., box turtles), are not able to synthesize beta-carotene well. In reptiles, conversion occurs in the intestines or liver, where it is later stored. 4 Vitamin A toxicity from dietary intake is unlikely to occur in herbivorous reptiles. For omnivorous or carnivorous reptiles, a diet including liver can cause dietary hypervitaminosis. SIGNALMENT Reptiles typically affected by this disease are carnivorous or omnivorous tortoises, such as box turtles and aquatic turtles. 1 There is no age or sex predisposition. PRESENTATION In reptiles, the clinical signs of hypervitaminosis A are typically manifested in the skin. 2 The signs are dry, scaly skin; skin ulceration and/or sloughing to various degrees; depression; lethargy; anorexia; weight loss; and/or dehydration ( FIGURES 1 AND 2 ). 1-3 Hypervitaminosis A in Reptiles Joerg Mayer, DABVP, DACZM/ECZM Joyce Huang, BSFR, University of Georgia, Athens, Georgia MANAGEMENT STRATEGIES shutterstock.com/Elina Leonova AVOID OVERSUPPLEMENTING The key to preventing hypervitaminosis A is to ensure reptiles are fed a well-balanced diet.

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