Metabolic bone disease

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What is MBD?

First of all, MBD stands for Metabolic Bone Disease or Metabolic Bone Disorder. It is a very common and well recognized syndrome found in reptiles as well as other animals and people. Other names MBD can go by are fibrous osteodystrophy, osteomalacia, secondary nutritional hyperparathyroidism, osteoporosis, and rickets. But these are more genetic terms and most people will only see MBD as a lack of calcium in the diet; however, it has more under laying causes and is more complex.

What causes MBD?

The primary cause for MBD is a lack of calcium or vitamin D3 in the reptile's diet, although reptiles can also be born with MBD if the mother has not received enough calcium whilst being gravid.

Other causes include:

  • Too little calcium and too much phosphorus: the ratio should be 2:1, and lack of D3 and other nutrients can prevent the absorbtion of calcium. D3 can come in forms of UVA/UVB light or in powders such as Nutrobal
  • Inadequate protein
  • Cool temperatures as they impair digestion and therefore calcium absorption.

MBD is a result of improper calcium to phrosphrus levels. When the calcium levels are low, the body has to try and take calcium from somewhere else to compensate; for example, calcium may be leached from the bones. This makes them softer, making them easier to fracture or break. Calcium also impacts a number of other physiological systems including muscle contraction and blood clotting. The ratio 2:1 (calcium:phosphorus) is ideal for controlling this, although calcium metabolism is not so simple, as vitamin D (D3) also plays a vital role. Because reptiles don't absorb vitamin D so well, they need ultraviolet light exposure in order to manufacture their own.

Feeding supplements as a sole source of D3 can be very dangerous to the uromastyx health, as D3 can reach toxic levels in their bodies. Nobody knows how much is too much and how much is too little; however, again bear in mind that these creatures cannot metabolise supplemental (man-made) D3 well enough for it to have a significant benefit.

A nice simple way to look at this is a well-balanced herbivore diet + UVB exposure = D3 production = successful calcium intake. Again, a secondary basking site with little to no UVB will allow the uromastyx to move in and out of the UV depending on the D3 levels in their bodies. This will alleviate stress as they can still get up to PBT (preferred body temperature) under the non-UV basking site, if needed.

Cross-species problem

One notable feature of MBD is that it is so low-level that it occurs in any creature which requires vitamin D3 and calcium to maintain its structural system. Deficiency of these compounds in humans is exactly the same as in reptiles; severe deficiency ends in MBD (also known as rickets), but mild deficiency in a large percentage of the population goes un-diagnosed. Reptiles and humans alike can live without knowing that their immune systems are compromised and their bodies are not functioning at peak efficiency.

Signs and symptoms

Symptoms may vary, as it depends on how long the reptile has had the disease, among other factors. But typical symptoms to look out for are:

  • Bowed or bent/twisted legs/limbs
  • Receded lower jaw line
  • Softening and swelling of the jaw which almost looks like rubber
  • In severe cases arching in the back and tail
  • Lethargy
  • Going off food due to not being able to eat because of rubber jaw or cannot hunt
  • Muscle twitches and in worse cases seizures due to lack of calcium in diet. As calcium not only affects bones but causes impaired nerve function, major organ damage and even damage at a cellular level
  • Constipation and/or prolapse
  • Fractures of the bones due to bone weakness
  • Muscle weakness and partial paralysis

Note: in some cases, the lizard may be observed standing with its foot bent underneath; however, this is known to be normal behaviour and there is a good chance that it is not related to MBD. If you observe this effect, however, you should still keep an eye on your lizard just in case.

Treatment

Depending on how advanced it is, the disease treatment can be costly, and depends on whether the disease has been caught in time. All cases should be seen by a proper herpetological veterinarian as X-rays and blood tests will need to be carried out to check for bone density and calcium levels. Once MBD has been confirmed, treatment can begin. The important thing to realise is that although MBD cannot be cured, it can be halted - the damage already done to organs and bones cannot be undone, but MBD as an actively progressing disease can be stopped.

For mild cases, MBD is treated with a change in diet, i.e. more calcium added and proper husbandry ensured. For more severe cases, the reptile normally need more treatments like calcium injections and vitamin supplementation, and possibly therapeutic use of a higher than normal level of UVB to aid recovery and utilisation of supplimentary calcium, which will probably be carried out by your vet. They may also need help with eating again if they have stopped eating. This, again, is best carried out under the supervision of your herp vet, so you can give the best help to your reptile.

Prevention

The best way to prevent MBD is through proper husbandry; the old axiom prevention is better than cure is certainly true here. Make sure you research any reptile/pet you buy first and problems like this may be avoided in the future.

The best prevention tips are as follows:

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