Metabolic Bone Disease in Reptiles: Causes, Symptoms & Prevention

What is Metabolic Bone Disease (MBD)?

Metabolic Bone Disease (MBD) is a term used to describe a group of disorders in reptiles caused by imbalances of calcium, vitamin D3, and phosphorus. It predominantly affects captive reptiles like bearded dragons, leopard geckos, green iguanas, and various tortoise species. These conditions include secondary nutritional hyperparathyroidism, osteomalacia, fibrous osteodystrophy, rickets, and osteoporosis. MBD leads to painful, weakened bones and can be fatal if untreated, but importantly, it is largely preventable with attentive care.

Causes of Metabolic Bone Disease in Reptiles

MBD primarily results from a lack of calcium and vitamin D3. Calcium is essential for nerve transmission, muscle movement, and skeletal health. Vitamin D3, produced in the skin of daylight-active reptiles exposed to UVB light (wavelengths 270-290nm), helps the body absorb calcium effectively.

When pet reptiles lack sufficient dietary calcium or UVB lighting, their blood calcium levels drop, a condition called hypocalcaemia. The body compensates by producing parathyroid hormone, which draws calcium from bones to maintain blood calcium, causing bone weakening and deformities characteristic of MBD.

Preventing MBD: Essential Husbandry Practices

Proper prevention hinges on ensuring reptiles receive adequate calcium and vitamin D3. Insectivorous lizards like bearded dragons and leopard geckos should be fed a varied diet of gut-loaded live insects dusted with calcium powder supplements. For vegetarian reptiles such as tortoises and iguanas, high-calcium leafy greens like dandelion, mustard greens, and watercress combined with calcium dusting are vital.

Providing full spectrum UVB lighting is equally important. Specialist UVB bulbs help synthesize vitamin D3 necessary for calcium absorption. These lights should be placed 5-10 inches from the basking area and replaced every six months to remain effective. High wattage mercury vapour lamps provide both heat and UVB, suitable for larger reptiles. While vitamin D3 powder supplements exist, they currently complement but do not replace UVB lighting.

Do Snakes Get MBD?

Carnivorous snakes typically do not suffer MBD as their diet of whole prey (rats, mice) provides sufficient calcium and vitamin D3 naturally. The prey's tissues contain bioactive calcitriol, aiding calcium metabolism. Exceptions include specialist snakes like rough green tree snakes and garter snakes who require additional supplementation due to their unconventional diets.

Recognising the Symptoms of MBD

Early signs include:

• Depression and lethargy; affected reptiles may stop moving or become listless. Brightly coloured species may darken in skin tone.
• Swelling and deformity of limbs; reptiles may have difficulty walking or refuse to climb as bones weaken.
• Jaw swelling and pain leading to decreased appetite and weight loss.

If untreated, more serious symptoms develop:

• Muscle tremors, seizures, and loss of coordination.
• Bone fractures, bending, twisting of limbs, and joint dislocations.
• Skull and jaw deformities, sometimes causing tongue protrusion.
• Spinal twists and potential paralysis.
• Digestive problems such as stomach bloat and gut infections.
• In tortoises, the shell may soften and deform, putting pressure on internal organs.

Left untreated, advanced MBD often results in death due to cardiac or respiratory failure.

Diagnosis and Treatment

A vet diagnosis involves clinical examination, blood tests to check calcium and parathyroid hormone levels, and X-rays to assess bone abnormalities and fractures. Treatment focuses on supportive care: ensuring proper hydration, administering injectable calcium, setting fractures, providing UVB lighting, and nutritional support.

Weak reptiles may require tube feeding and careful handling in a simplified enclosure to prevent injury. With prompt and careful treatment, many reptiles recover partially, though some permanent deformities may persist. In severe cases where suffering is extreme, humane euthanasia may be recommended to prevent further distress.

Conclusion

Metabolic Bone Disease, though serious and painful, is avoidable. Responsible reptile ownership means providing balanced diets, adequate calcium and vitamin D3 supplementation, and appropriate lighting to support natural physiology. Regular observation and veterinary check-ups can catch early signs, enabling timely treatment and promoting long, healthy lives for your scaly companions.