(Nutritional Osteodystrophy, Osteomalacia, Secondary Nutritional Hyperparathyroidism, Rickets)
Metabolic bone disease (MBD) is the most common diet-related illness of pet reptiles. This disease is particularly a problem in herbivorous reptiles such as tortoises and green iguanas, though MBD occurs in many other species of lizard as well.
While metabolic bone disease is a potentially fatal illness, it is also entirely preventable. Metabolic bone disease is almost always a case of poor husbandry. By providing your pet with the correct diet and its proper environment, you can ensure that your reptile does not go on to develop MBD.
What is metabolic bone disease?
Metabolic bone disease is essentially an improper balance of calcium, phosphorous, and Vitamin D in the body. A normal dietary calcium: phosphorous ratio should be in the range of 1.2:1 to 2:1. An imbalance in the ratio causes the body to have too much phosphorous in the blood and not enough calcium.
The body compensates for this by taking calcium from the bones. As bones are depleted of calcium, they become soft and brittle, and prone to fractures. Vitamin D also contributes to proper calcium metabolism. Vitamin D is synthesized in the skin by UV light, and is responsible for increasing the amount of calcium absorbed by the body.
What are the causes of metabolic bone disease?
There are several factors that contribute to the disease:
• Lack of dietary calcium
• Improper calcium : phosphorous ratio in the diet
• Vitamin D deficiency
• Incorrect temperature gradient
• Lack of exposure to UV light (whether via unfiltered sunlight or UV bulb)
• Disease of the kidneys, liver, thyroid or parathyroid glands (rarely cause MBD)
How can I recognize if my reptile has metabolic bone disease?
Many pet owners are unaware that their pet has developed MBD, as many animals can appear deceptively healthy. Unfortunately, this sometimes means that the disease is well-advanced before it is diagnosed.
Signs to look out for in your pet reptile are:
• Bowed or swollen limbs (often appear well-muscled)
• Soft and swollen jaw (“rubber jaw)
• Receding or deformed lower jaw
• Spinal deformities
• Twitching limbs
• Broken bones due to bone weakness (mainly legs)
• Lameness
• Anorexia
• Lethargy
• Constipation
• Inability to support body weight on limbs
• Tortoises/turtles have softening or deformities of the shell
• Green iguanas will become brown colored
How is the disease diagnosed?
If you suspect your pet may have MBD, do not delay in bringing it to a vet. The veterinarian will diagnose the disease based on dietary history, husbandry (e.g. lack of a UV light), and physical exam. X-rays may also be necessary to confirm the diagnosis, or to gauge how far the disease has progressed. Blood samples are occasionally taken to test for concurrent disease.
Is it possible to treat metabolic bone disease?
Treatment will depend on the severity of the disease. Simply adding more calcium to the diet is not enough.
The diet must be corrected immediately. Herbivores should be encouraged to eat plants that are nutrient-dense and rich in calcium, such as dandelions, alfalfa, squash, cabbage, kale, bok choy, okra, sprouts, collard greens, etc.
Carnivores should be fed whole captive-bred prey. The vet may also suggest a calcium supplement that can be dusted onto the food (e.g. Nutrobal). It is important to discuss with your vet what your pet’s ideal diet consists of.
The husbandry of the reptile’s environment should be improved as well. If one is not present already, a UV bulb should be added to the vivarium. Proper temperature gradients should be maintained, as well as regular light and dark cycles. Ensure that your pet’s enclosure is large enough to move around in and exercise.
For severe cases, further treatment may be necessary. Animals with soft jaws may have to be force fed with baby food and calcium supplement. This requires gentle handling so as to avoid fractures and stress anorexia. Calcium injections are given to reptiles with severe muscle tremors that indicate hypocalcaemia (e.g. dangerously low levels of calcium in the blood).
Calcitonin therapy will also speed recovery, but is less frequently used. Calcitonin inhibits calcium resorption from the bones.
Metabolic bone disease is a difficult disease to treat, and can ultimately prove fatal for your pet. Reptile owners should have their pets examined by a veterinarian once a year, whether it shows signs of illness or not.
You should consult with your veterinarian to ensure that you are feeding your pet an adequate diet and keeping it in its proper environment. Early preventative measures will provide your pet with a longer, healthier, and happier life.
(photo: djpmapleferryman)