Metabolic Bone Disease (MBD) - what is it and how do you fix it?

Metabolic Bone Disease (MBD) is unfortunately a common disease of reptiles due to lack of dietary calcium, imbalanced nutrition and/or lack of UVB rays. UVB rays from either unfiltered sunlight or a UVB producing bulb are needed in reptiles to produce Vitamin D3 in the skin, which is necessary to absorb calcium from the food and supplementation. Without UVB rays then your chameleon cannot absorb the calcium you are giving it. If you are not providing an adequate level of calcium in the diet then no amount of UVB will make up for it. Too high levels of phosphorus in the diet will interfere with calcium absorption so even with good calcium levels and UVB the body is still not getting enough. There are many body processes that require calcium, such as muscle contraction, energy metabolism, intestinal movement, nerve conduction, blood vessel function, and bone strength. To compensate for inadequate calcium absorption the body will pull calcium directly out of the bones where it is stored so there is enough calcium for critical functions like muscle movement and metabolism. This causes the bones to be very weak, even to the point of bending or breaking very easily. Chronic calcium deficiency causes continued damage to multiple organs, eventual organ failure and death. Lack of sufficient calcium for muscle movement can lead to constipation and very often egg binding in females, which is life threatening in itself. Due to the calcium deficiency affecting entire body in drastic way these chameleons can easily develop concurrent illnesses, such as respiratory infections, eye infections, etc. Calcium needs are the highest during the first year of life while bones are still growing so it is often young chameleons that are most affected. There are rare cases of metabolic disease occuring despite proper calcium and UVB and a congenital component is suspected, though not confirmed. Almost every instance of MBD can be completely attributed to deficiency in care.

By the time symptoms of metabolic bone disease are apparent the disease is already advanced and there is a severe calcium deficiency. Signs of MBD include stunted growth, bent legs bones, fractures of those bones (double elbows or knees), grabbing at its own legs, tongue not shooting as far, a 'rubber' jaw, the mouth doesn’t close all the way, etc. The most notable symptoms are bent legs and multiple elbows or knees, which are actually fractures of the leg bones. Bloodwork will show an elevated phosphorus level that may be the same or higher than the calcium level, which is abnormal. There may also be evidence of other organ damage, especially with the kidneys. On x-rays the bones will appear to have poor density and may not even be visible in the end stages because there is so little calcium left.

Metabolic bone disease does not happen over a course of days. It takes weeks to months of persistently inadequate care to cause the symptoms associated with calcium deficiencies. It is very important to take action as soon as symptoms are recognized as the disease is already in the advanced stage. Damage caused by metabolic bone disease cannot be reversed completely but the disease process can be stopped so there is not further damage and the bones can heal if proper UVB is supplied and the imbalance of dietary calcium is addressed.

Metabolic bone disease takes a long time to develop, and conversely takes a long time to resolve. Correcting your husbandry and providing adequate calcium, nutrition through gutloading, and UVB is the first critical step. However, the deficit of calcium needs to be addressed with additional supplementation before the body can function normally and begin to heal. A small drop of liquid calcium (without D3) can be given twice daily for a month to replace the calcium deficit. A vet may have to give injectable calcium to replace the deficit in more than mild cases. UVB, especially in the form of unfiltered sunlight, is essentail. If there are broken bones already unfortunately they will need time to heal on their own. If a cast or splint is applied it can actually cause more breaks to occur since the bones are so weak. A hospital cage that is shorter with wider perches and a towel on the bottom to cushion falls should be provided to prevent further injury. It is very important to address MBD as soon as symptoms are noticed to stop the damage being done.

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