Metabolic Bone Disease

MBD is a general term used to describe multiple conditions and diseases that are caused by improper metabolism of calcium due to an imbalance of vitamin D3, calcium or phosphorus. The disease is a result of poor husbandry and causes softening or thinning of the bones and sometimes overproduction of supportive connective tissue (especially in the jaw, sometimes called ‘rubber jaw’).

The disease is commonly associated with reptiles and frogs that require ultraviolet light (sunlight) for the production of vitamin D3. Vitamin D3 is necessary for the body to absorb calcium. Calcium is a major mineral component of bones.


  • Low levels of calcium or vitamin D3 in the diet.
  • High levels of phosphorus or vitamin D3 in the diet.
  • Poor environmental conditions, particularly those that impair digestion and calcium absorption (e.g. cool temperatures, lack of exposure to UVA light)
  • Insufficient exposure to ultraviolet A (UVA) and ultraviolet B (UVB) which are necessary for the production of vitamin D3

Symptoms: MBD is a gradual process and is typically at an advanced stage by the time symptoms become visible. Symptoms include swollen limbs, bowed legs, softened or hanging jaw, lumps along the spine or limbs, general weakness, fractured bones, inability to climb or hold body off the ground, paralysis, muscle tremors or jerky movements, weight loss, appetite loss, constipation. In turtles, the shell may become soft, domed, or the edges turn up.

Arboreal (tree dwelling) species are likely to spend more time on the ground due to an inability to climb.

Risks: Risk of MBD is highest when reptiles or amphibians do not have access to a varied diet, unfiltered sunlight and calcium in their diet. Natural sunlight or UVB light is necessary for the production of Vitamin D3, which the body uses to absorb calcium. Note that glass and Perspex / plastic screens, as often used on outdoor enclosures, block UV light, and mesh will filter various amounts of it.

A UV meter is available for use for NZHS members to guide in enclosure design, construction and placement.  Check out the details here.


Duvaucel’s gecko with MBD- note the lump on the spine. © Chris Wedding 
Wild Ngahere Gecko, radiographic images showing bone deformation © Joel Knight