Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Metabolic Bone Disease: An Avoidable Threat for Reptiles

Pet Column for the week of January 14, 2002

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Jennifer Stone
Information Specialist

An iguana was brought in to the clinic where I worked because of a suspected fracture in its left forelimb. The doctor did a physical exam and then ordered a radiograph so that we could see the fracture. What we saw on the radiograph was astonishing. The bones that should have appeared white were either a pale gray or not present at all. This lizard literally had no bones!

Dr. Julia Whittington, an exotics and companion animal clinician at the University of Illinois Teaching Hospital in Urbana, says, "The reptile owner's goal should be to mimic the reptile's natural habitat as closely as possible in order to avoid diseases like this. The sad part about this kind of problem is that it is completely avoidable."

Metabolic bone disease develops in lizards for several reasons. Some lizards, such as iguanas, that eat primarily vegetables and in captivity can develop a calcium deficiency if they are not fed foods high in calcium such as kale, collard greens, and turnip greens. Many owners make the mistake of assuming that a vegetable such as iceberg lettuce has sufficient nutritional value when in reality it is mostly water.

Yet calcium alone cannot prevent this disease. Vitamin D3, which is produced in response to exposure to direct UV light, is also necessary for reptiles to utilize calcium. If a reptile is not receiving appropriate amounts of UV light, metabolic bone disease may develop despite a calcium rich diet.

Reptiles such as bearded dragons, geckos, chameleons, (and some amphibians such as frogs, and salamanders) that eat insects instead of vegetables, face other dietary concerns. The body must maintain an equal balance of calcium and phosphorus, and the exoskeleton of most insects is rich in phosphorus. If there is a large amount of phosphorus in the diet then calcium will be removed from bone in order to maintain this balance, which over time can lead to a major loss of calcium from the bones (metabolic bone disease). In order to avoid this problem, the insects can be dusted with a calcium powder or can be fed a diet highly supplemented with calcium.

Since only UVB (and not UVA) light will trigger calcium utilization, a special lamp may be purchased through a pet store. Standard plant grow lights should not be used because they put out only UVA light. Nocturnal reptiles may benefit from the use of a black light, which also provides UVB light. Since UVB bulbs will only continue to put out the UVB light for about 6 months, bulbs should be changed frequently. To ensure adequate exposure, UVB light must be shown directly on the reptile and not through glass or plastic.

Metabolic bone disease is seen most often in young growing reptiles, but older reptiles are occasionally affected. Signs may include fractures, a soft, rubbery jaw, a decrease in appetite, a reluctance to move and muscle tremors. Radiographs are the best way to diagnose bone loss.

Treatment of this problem should start with correcting the light and/or calcium deficit. Sometimes a calcium supplement is given along with Vitamin D3. Calcitonin, a hormone that promotes the deposition of calcium into bone, may also be given. Finally, cage rest is essential for a reptile suffering from metabolic bone disease. Any movement (especially climbing) can lead to multiple fractures when the bones are so fragile.

Dr. Whittington suggests that those thinking about getting a reptile should, "find out about its natural habitat and discuss these issues with your reptile veterinarian before it becomes a problem." If you have a question about metabolic bone disease, please contact your local exotic veterinarian.