A Quick Guide to Metabolic Bone Disease (MBD)

It’s the ailment that scares nearly all reptile keepers the most. It worries us and sends us online to do hours of research on proper lights, hoods, and vitamin supplements. And we hear about it continuously in online groups or forums. MBD, MBD, MBD, over and over again. Unfortunately, it is one of the leading causes of unnecessary (and easily preventable) death in captive reptiles, and it hits young, growing animals particularly hard. What is it, how do we prevent it from happening to our pets, and how do we recognize if an animal has it?

What is MBD?

MBD is the acronym for Metabolic Bone Disease, which is a catch-all term for a condition in which (in summary) the body cannot metabolize calcium properly and in severe cases leads to the bones of the body becoming brittle and rubbery, and problems with muscles and the nervous system. If it sounds painful it’s because it is; untreated, chameleons and other reptiles with severe MBD will develop brittle bones that can break, bend out of shape, and cannot support their movements. Chameleons can develop tremors (hypocalcemic tetany), problems moving, lethargy, digestive issues, and eventually death.

The good news is that is is preventable, early all cases of MBD could have been easily avoided. It is like heartworm in dogs; extremely easy to prevent but serious once the infestation has set in. Thankfully, MBD is also treatable and although broken or misshaped bones may never heal and look completely normal, the bone density can be corrected and the body brought back into balance. 

What Causes MBD?

There are a few other rare causes, but for nearly all cases of MBD this is where the blame lies:

MBD in the tail of a Meller's chameleon.

LIGHTING: I have written about The Importance of UVB before, but in short, chameleons and other diurnal reptiles absolutely need and depend on UV light to form strong bones. Specifically the UVB range of the UV spectrum is what helps reptiles form vitamin D in their skin. This vitamin in turn helps metabolize calcium and maintain healthy blood calcium levels. It’s the same for us; healthy bones need calcium as well as vitamin D.

It is vital that chameleons have a linear (tube style) fluorescent UVB bulb across the cage, on 10-12 hours a day, so they can bask and produce their own vitamin D. Some good bulbs to consider are the Reptisun 5.0 or 10.0 or the Arcadia 6% or 12% lights, as examples (the new high-output T5 bulbs are better, but the T8 are fine). Each bulb will have a different life span of UV radiation, but they should be replaced every 6-12 months depending on the brand, to ensure that they are always going strong. And make sure that the fixtures never have a plastic cover, as UVB cannot go through glass or plastic. 

SUPPLEMENTS: The second major cause is improper supplementation. I’ve written at length about what Vitamins and Minerals Do (and Why They Matter) and on Which Supplement is Best and Why, but as a quick summary this is the stuff to know:

Calcium is (as we all know) absolutely necessary to build strong bones. A lot of the insects we feed are not very high in calcium so we find it necessary to correct this by dusting feeders lightly with calcium powder. Occasionally a calcium or multivitamin containing artificial vitamin D3 can be given, to fill in any potentially gaps the UVB bulb may not be covering. Here, people tend to make one of two mistakes:

Either their give too little calcium at all or they give way too much vitamin D3

But Olimpia, you’re thinking, that makes no sense. Didn’t you just say vitamin D is important? Yes, dear reader! But the skin can make as much or as little vit D as it needs, whereas oral supplement vit D is (in short) fat-soluble and will build up in the body, with nowhere useful to go. Too much and it actually starts to work against us – getting in the way of absorbing calcium, calcifying the soft tissues, and causing MBD too. So to keep this short and sweet; a little vitamin D3 in the diet is a great idea, but too much (ie. daily) will lead to complications.

A little goes a long way with vitamin D! With most brands 2-4 times a month will do, depending on your chameleon species. 

What Are Some Symptoms of MBD?

Veiled chameleons with MBD. Broken arms, malformed casques, etc. are all physical signs. 

I’ve already mentioned the bone deformities, so I’ll start there. Calcium is used for a ton of other things in the body besides just bones and teeth; it is almost like a fuel that powers the muscles of the body, so your arms move, your gut contracts, and your heart beats thanks to calcium. Your bones are obviously the scaffold of your body, but they serve as a calcium reserve as well. So when the body isn’t taking in any additional calcium, muscles and organs start to pull from the only place they can; the bones.

Soft bones, breaks, and asymmetry in the bones are all physical signs. The bones in the arms and legs should be nice and straight with a single elbow/knee join. Two or three “elbows” in an arm mean that the bone has broken in a couple places. The edges of the mouth should be straight. The spine and tail should be nice and straight also with no serpentine curves.

Other physical signs include tremors and clumsiness. Remember how calcium is used in the muscles? Without enough calcium to work properly you’ll start to see signs like muscle tremors in the arms and legs, particularly when walking, trouble moving around normally, lethargy, problems shooting the tongue at food, and even constipation.

What a healthy young veiled (female) should look like. 

Another healthy veiled chameleon female. Nice straight limbs, straight casque, and straight spine. 

How Can MBD Be Treated? Is it Curable?

The first step in treatment is to reach out to a vet for assistance. Depending on what the root cause is, changes to the cage and/or diet will definitely need to be made. But a veterinarian can give an injection of calcium to start recovery and can help you with the correct dosage of an oral liquid calcium (if necessary) for as part of treatment. I highly discourage anyone from administering medicines at home without the guidance of a professional, even though liquid calciums like calcium glubionate are easily available online. You want to return the body to a state of balance carefully, properly, and slowly, so not over-doing it is important as well.

It is possible to stop MBD, return the blood calcium levels to where they should be, and re-solidify the bones again. However the breaks and curvatures in the bones may never correct themselves entirely (so the animal may always be somewhat malformed) and it’s difficult to determine how much permanent organ damage may have occurred. But with veterinary assistance and changes to husbandry, animals suffering from MBD can be treated and go on to live normal or nearly-normal lives for some time. 

In severe cases where moving around is difficult or dangerous for the animal, a hospital cage might be necessary. To learn how to make a hospital cage, check out my article for Reptile Apartment, How To Make a Chameleon Hospital Cage. 

How Do I Prevent MBD?

Like I said earlier, the two main causes are either lighting and/or diet. When setting up a cage really invest in the best UVB bulb you can afford, and replace it often. Do research and ask breeders/experts what they recommend for your particular species and animal. Look into what supplements you need and often they should be used. When it comes to these two things don’t cut any corners – Don’t reuse a UVB bulb you found on Craigslist to save a few dollars (who knows how old it is!) and don’t go with the first product the pet store recommends because it’s faster than ordering a product online. It will be money and time well spent if it means your chameleon lives happily and healthily its entire natural lifespan. 

Metabolic bone disease is an easily preventable disease, and by taking just a few steps can be avoided entirely. And as always, if you still have questions please don't hesitate to ask!