Metabolic Bone Disease in Reptiles: Signs and Prevention

Quick answer

Metabolic bone disease (MBD) is a group of conditions in which a reptile's bones become weak, soft or deformed. In pet reptiles it is almost always caused by care problems: not enough calcium in the diet, too much phosphorus, too little vitamin D3, missing or old UVB lighting, or an enclosure that is too cold. Early signs include weakness, trembling and a reluctance to move; later come soft jaws, swollen or bent limbs and fractures. It needs a reptile vet, and it is largely preventable.

What happens in the body

Reptiles need calcium for bones, muscles and nerves. To absorb calcium from food, they need vitamin D3. Many species make D3 in their skin when exposed to UVB light, and they also need enough warmth to digest and use what they eat.

When calcium runs short, the body releases a hormone (parathyroid hormone) that pulls calcium out of the bones to keep blood levels up. Over weeks and months, the bones thin and soften. Vets call the most common form nutritional secondary hyperparathyroidism, and it is the most common bone disease seen in reptile practice.

Older reptiles can also develop a related problem from kidney disease, where failing kidneys upset the body's calcium and phosphorus balance. That form looks similar but has a different cause, which is one reason a vet check matters.

Who is most at risk

Young, fast-growing reptiles are hit hardest, because they need a lot of calcium for growing bones. The usual patients are:

• insect-eating lizards such as leopard geckos and young bearded dragons;
• plant-eating lizards such as iguanas;
• chameleons;
• turtles and tortoises, including red-eared sliders.

Snakes that eat whole prey get calcium from the bones of what they eat, so MBD is far less common in them.

Common causes

• No UVB, or the wrong UVB. A lamp behind glass, mounted too high, too weak for the species, or past its useful life. Our guide to UVB and heat lighting explains how to get this right.
• Too cold. Without a proper basking temperature, a reptile can't digest food or use nutrients well.
• Unbalanced diet. Most feeder insects are naturally low in calcium and high in phosphorus, so they need dusting with calcium. Many fruits are low in calcium too.
• No supplements, or the wrong ones. Skipping calcium dusting is a classic route to MBD in insect-eaters.
• Foods that bind calcium, such as spinach fed in large amounts.

Usually it's a combination. A gecko with no calcium dish and a dim lamp, or a slider fed only dried shrimp in a tank without UVB.

Signs to look for

MBD develops slowly, and reptiles hide weakness well. Learn what normal looks like for your animal.

Early signs

• Less active, weaker grip, reluctant to climb
• Eating less, or struggling to catch or chew food
• Twitching or trembling toes, legs or muscles, especially when handled
• Slower growth than expected

More advanced signs

• A soft, flexible or swollen lower jaw (sometimes called "rubber jaw"), or a jaw that no longer closes neatly
• Swollen, thickened or bowed legs
• Walking on the belly instead of lifting the body
• A kinked spine or tail
• Broken bones after only minor bumps or falls
• In turtles and tortoises, a soft, flexible or misshapen shell, or a shell that looks too small for the body
• Prolapse from the vent
• Severe tremors, spasms or seizures, which happen when blood calcium falls very low

A reptile with tremors or seizures is an emergency.

What the vet typically does

A reptile vet will ask detailed questions about lighting, temperatures, diet and supplements, because the cause is usually there. They'll examine the animal and often take X-rays to check bone density and look for fractures. Blood tests can show calcium and phosphorus levels and check the kidneys.

Treatment depends on how severe things are. It may include:

• Calcium supplements, by injection in severe or seizing animals, then by mouth;
• Fluids for dehydration;
• Assisted feeding if the reptile can't eat on its own;
• Pain relief and care of any fractures, sometimes with splints;
• Correcting the set-up: new UVB, proper basking heat and a balanced, supplemented diet.

Follow your vet's dosing exactly. More calcium or vitamin D3 is not better, and over-supplementing causes its own harm. Recovery takes weeks to months, often with repeat checks. The outlook is generally good when the problem is caught early and the reptile is still eating, but bones that have already bent or healed in the wrong shape usually stay that way.

At home, handle an affected reptile as little as possible, since fragile bones break easily. Remove high climbing branches and keep the enclosure simple until the vet says otherwise.

How to prevent MBD

• Give the right UVB for your species, mounted at the correct distance with nothing in between, and replace lamps on schedule.
• Provide a proper heat gradient with a measured basking spot.
• Dust feeder insects with calcium as directed for your species, and keep a dish of plain calcium powder for geckos.
• Gut-load feeder insects with good food for a day or two before feeding them.
• Feed a varied, species-appropriate diet. For plant-eaters, focus on calcium-rich greens; for turtles, a quality pellet plus greens and whole prey.
• Weigh and check young reptiles regularly, and book a vet check soon after you get a new animal.

Species guides such as leopard gecko care list the temperatures and supplements each animal needs.

When to see a vet

See a reptile vet promptly if your reptile:

• has a soft, swollen or misshapen jaw;
• has swollen or bent legs, or drags itself instead of walking;
• trembles, twitches or has spasms;
• breaks a bone or suddenly can't use a limb;
• has a soft or deformed shell;
• stops eating or loses weight.

Go immediately if it is having seizures, can't move, or has prolapsed tissue from the vent.

When buying a reptile, ask the seller what lighting and supplements they've used, and look closely at the jaw, legs and shell. You can browse reptile listings on Paalo and ask those questions before you commit.