MBD; Metabolic Bone Disease

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Metabolic Bone Disease:

By Christina Obrecht, January 24, 2008 1:05 PM PST

The Description:

Metabolic Bone Disease or MBD, is the collective name given to a number of symptoms and problems commonly seen in captive iguanas or other reptiles. Other names for MBD include, Fibrous Osteodystrophy and Secondary Nutritional Hyperparathyroidism. The bad news is that MBD is the most common ailment seen in pet reptiles. In fact, most reptile vets would agree that it is WAY TOO common. The good news is that it is easily preventable with proper care and is treatable if it is spotted early enough.


The Causes:

MBD can be caused by a variety of factors or a combination of factors, most of which are related to improper husbandry(housing). MBD is ultimately a calcium deficiency. It can be thought of as the reptile equivalent of rickets. Some cases of MBD are caused by hormonal imbalances brought on by other diseases. Most often, however, MBD is caused by one of the following factors: not enough calcium in the reptile's diet, lack of exposure to UVB lighting, and inadequate temperatures.

Calcium is a very important nutrient. In addition to other things, calcium is used to build bones, and plays an important role in nerve functioning. In a healthy animal, calcium is in balance in the body. It interacts with other nutrients, such as vitamin D3 and phosphorus, and is regulated by various hormones. Too much or too little of the calcium, the other nutrients it interacts with, or the hormones that regulate it, will cause the delicate calcium balance in the body to be thrown “off-kilter”. One of the causes of MBD in reptiles, is a lack of calcium in their diet. Reptiles should be given a diet that contains twice as much calcium as it does phosphorus. If the diet lacks calcium, the body will attempt to get it from some other source, and that means pulling it from the bones. MBD will result!

UVB lighting also plays a very large role in MBD prevention. Upon exposure to UVB, a reptile’s skin will manufacture vitamin D3. This vitamin plays an important part in regulating how the body absorbs and uses calcium. Without exposure to UVB lighting, either through artificial UV bulbs or, better yet, unfiltered sunlight, reptiles cannot manufacture vitamin D3. Without vitamin D3, their bodies cannot properly absorb and use calcium from the diet. The best way to provide your reptile with it, is by making sure it gets adequate exposure to UVB. This, along with providing a calcium-rich diet, is one of the most important preventative measures you can take to avoid MBD.

Lastly, making sure to keep your reptile at the right temperature is another way to avoid MBD. Since they are cold-blooded “animals”, they rely on their surroundings to provide them with the heat necessary to properly digest their food. Reptiles that are kept too cool will be unable to digest their food well, and will not adequately absorb the nutrients, including the calcium, available. This can also contribute to MBD.

There is another reason why a reptile may develop MBD - breeding season. This is really only a problem for females. As breeding season progresses, females develop eggs in their ovaries, even if they have not mated. As the egg shells develop, large amounts of calcium are needed. During this time, females are highly susceptible to MBD. Make sure that you keep a good eye on your females during breeding season. Extra calcium should be provided during this time.


MBD may manifest itself in many ways. Most often, the first symptom to appear is thin, easily broken bones. Many owners do not realize that their reptile has MBD until it breaks a bone doing something that a healthy reptile would have no trouble with, such as climbing or jumping. As bones weaken, the body will attempt to strengthen them by laying down fibrous connective tissue at the points of strain. This will often result in swollen, “Popeye” legs. The legs may feel bumby to the touch. They may become bowed as the weak bones bend under the pressure of the muscles pulling on them. Breaks may result in permanent paralysis.

Another common symptom of MBD is a soft or spongy lower jaw bone. Like the limbs, the jawbone may swell as connective tissue is laid down to replace lost bone. Eating may become difficult or painful, resulting in lost appetite. In severe cases, the bottom jaw may recede from the top or grow at a slower rate, resulting in an overbite which contributes more to eating difficulties. The overbite may also lead to gum abrasions and other related problems.

If MBD affects the nerves, trembling or weakness in the limbs may occur. In worst cases, partial paralysis may result. Often this is evident in the back legs and tail. The reptile may drag itself along with its front legs. It will be unable to climb or get around properly.

Any of these symptoms will proceed a lizard that doesn’t feel well. Lizards suffering from MBD will often show general signs of illness, such as lethargy, weakness and lack of appetite. If you see any of these symptoms, your lizard may have MBD and should be seen by a vet immediately! If left unattended, MBD can permanently maim or kill your lizard.


Thanfully, MBD can be reversed if it is treated early enough. There are many courses of action that may be taken to treat MBD, depending upon the severity and particulars of the case. Broken bones will be set and allowed to mend. Extra calcium and exposure to UVB light will be given. Any other necessary changes in housing will be recommended. Physical therapy may be applied to weakened muscles and paralyzed limbs. Many of the symptoms can be reversed. Trembling, weakness, and partial paralysis will often go away once treatment has begun. Bones will become strong again, and appetite will return.

Some things, however, will be there forever, even long after the reptile has recovered from MBD. Distorted jaws, toes, backs and limbs will remain. Normal movement and climbing activities may still be restricted. Pain may continue. Females may be unable to lay eggs due to her twisted spine. As a result, she had to undergo an emergency spay. Problems with defecation may occur for the same reason. And, of course, any spinal cord injuries obtained from broken backs will result in permanent paralysis.


Many reptiles have recovered from MBD and lived fulfilling lives, despite permanent physical deformities. But why put your pet through such a terrible experience when MBD is so easily preventable? It is extremely telling that wild reptiles do not suffer from MBD. This disease is completely the result of improper care in captivity. You are your pet’s caretaker. It relies on you for everything it needs. Do not let them down, for it will surely suffer for it.


Don't let this happen to your reptile!

This was an 18 year old green iguana who didn't have such a happy ending. Most of the time MBD is irreversable; but in some cases can be reversed if not too far in advanced. Unfortunately, this is a big killer in reptiles; I have noticed that with a lot of the reptiles that I have rescued. They need the proper lighting and vitamin supplements. Please help them!