Metabolic Bone Disease

Metabolic Bone Disease is still depressingly common in captive reptiles, this is actually a group of conditions that all have the same ending – a slow, painful death for the animal that is unfortunate enough to have them. This article is in no way intended to be used to diagnose your pet – it’s not just reptiles that get it! – but to give you a little more information to help you understand how and why it happens.

Remember: if you are concerned about your pet’s health, SEE A VET. It’s a legal as well as a moral duty if you own animals.

So what do we mean by Metabolic Bone Disease (MBD)?

In layman’s terms, when a reptile does not have enough calcium in the bloodstream to use in its cells, it goes to one store of bodily calcium that is present in all vertebrates: the skeleton. Calcium is leached from the skeleton to keep other bodily functions going, and as a result the bones get softer and have to be reinforced with fibrous tissue. At this point the keeper begins to notice their pet has a problem, and if the cause is not corrected quickly then the animal soon dies.

There are many different conditions that can lead to the obvious signs of MBD, but we’re concerned with just two: nutritional secondary hyperparathyroidism and renal secondary hyperparathyroidism. The first is the commonest, and is usually caused by a lack of calcium in the bloodstream because the animal is unable to use the calcium in its diet. The second is rarer, and relates to an increase in phosphorus in the system due to kidney (renal) failure. This raise in the levels of phosphate in the blood leads to the parathyroid gland releasing a hormone that demands the body find more calcium to re-balance the calcium/phosphorus levels, which leads to bone being broken down. The first is much more likely, although if you suspect either then please take your pet to see a vet!

What are the symptoms? 

Early symptoms are bowed or swollen limbs, flexibility of the jaw (sometimes called ‘rubber jaw’), arched spine, difficulty moving or a reluctance to move, sudden aggression when picked up, and softening of the shell in tortoises and turtles. It’s a very painful condition, so the animal sometimes walks with a jerky, hesitant gait, can have twitches and tremors and even have seizures. Eventually they experience complete collapse, followed by death.

Why is calcium so important?

Calcium is used as part of the mechanism to send and receive nerve signals, to help with the formation of blood clots, to create strong bones and teeth, to regulate the release of certain hormones and to regulate the contraction of muscle cells. It is vitally important in regulating the heartbeat, so you can see that it’s an essential substance in the body.

Where does the body obtain its calcium?

Usually, calcium is found in the diet. In our pet lizards and amphibians, this is added to with a powdered supplement and sometimes with allowing the animal access to a bowl of powdered calcium, cuttlefish bone, or blocks of calcium carbonate. Snakes get theirs from the bones of their prey.

So if I give my reptile calcium, it can’t get MBD.

Not true. Your pet needs certain things in order to metabolise calcium and use it within the body. In simple terms they need vitamin D, which is obtained through dietary sources and exposure to UVB light, all of which requires correct body temperatures in order to work correctly. The actual process is astonishingly complex, but as pet keepers we just need to know UVB, heat, calcium! How we provide each of those things is mostly unimportant, as long as we provide them. 

Phosphorus is also important. The ideal calcium/phosphorus ratio is 1.5:1 to 2:1 (twice as much calcium as phosphorus), which is why it’s important to use a source of calcium that is phosphorus free.

Certain foods contain compounds that bind to calcium, reducing the amount available within the body. Food high in oxalates – such as spinach – can do more harm than good if they form a large part of the diet.

How do I stop my reptile from getting Metabolic Bone Disease (MBD)? 

• Provide a varied diet, appropriate to the species you are feeding. Make sure that livefoods have been well fed on a variety of foods in order to supply all the different micronutrients that are needed by your pet’s system, and be sure that you are aware of potential problems with the vegetable part of the diet for herbivores and omnivores. 
• Ensure that your pet is kept within the correct temperature range for its species. If its body is too cold, it cannot use the nutrients you are supplying it with.
• Artificial sunlight – the magical UVB! With the wide range of different light sources available these days, there is no excuse for not providing at least some level of UV light.
• Correct bodyweight. A diet high in fat can cause problems with calcium absorption, and an overweight animal is less likely to be able to regulate its body temperature than one of the correct weight. Make sure your pet has an appropriately sized enclosure, with enough enrichment to keep them active.

If you’ve read our article on impaction, you might notice that a lot of the causes of these two awful conditions are very similar. Prevention of them both is the same, too; correct husbandry! If you are not sure, then please ask; we’re here to help, and we can make sure that you are armed with enough knowledge to prevent this dreadful condition ever being a problem for your pets.

One last thought. If you are worried that your pet is unwell, take it to a vet!