Metabolic bone disease (MBD) is a term that refers to a collection of medical disorders that affect the form, integrity, and function of bones. This disease is the most common cause of skeletal abnormalities and changes in gait in reptiles.
Secondary nutritional hyperparathyroidism is the most common form of MBD. This is caused by inappropriate diet (calcium or vitamin D3 deficiency or calcium to phosphorus ratio imbalance) or inadequate exposure to ultraviolet (UVB) light. When there is not enough calcium in the body for normal metabolic processes, the parathyroid gland is stimulated. This ultimately causes the body to pull calcium from the bones, which weakens them. Signs of this disease include soft or rubbery bones, malformed bones, inability to walk or climb normally, swelling of limbs, pathologic fractures, cloacal or rectal prolapse, muscle fasciculations, tetany (cramps of muscle spasms), tremors, lethargy, decreased appetite and stunted growth. More commonly affected reptiles include lizards/geckos and chelonians (turtles/tortoises). Characteristics of MBD can be appreciated on exam and seen on x-rays.
Most diurnal lizards/geckos and chelonians require UVB light exposure to synthesize vitamin D3. This vitamin is needed to ultimately absorb calcium in the gastrointestinal tract. Without UVB light, calcium supplementation on food cannot be fully utilized by the body. Unless your reptile is kept outside under natural sunlight, it will need an artificial UVB spectrum light. This light should ideally be the length of the enclosure and needs to be replaced every 6 months. There may still be visible light, but the UVB spectrum fades after this time.
It is important for diurnal reptiles to have calcium supplementation since most foods provided have inadequate levels. All insects, most fruits, some vegetables, and even organ/muscle meats are deficient in calcium. Appropriate calcium supplements should not contain any other vitamins or phosphorus. Gut loading insects (filling feeder insects with a nutritious diet 24-48 hours prior to feeding them to your reptile) also helps increase calcium in the diet. I will discuss this further in a later post.
If you have any questions about metabolic bone disease, or you are concerned about your reptile, please schedule an appointment with one of our knowledgeable veterinarians.