Metabolic bone disease (MBD) is a well-recognized and common disease seen in pet reptiles. Metabolic bone disease results from an improper calcium to phosphorus ratio in the body, causing softened and damaged bones. Other terms which may be used for this disease include fibrous osteodystrophy, osteomalacia, secondary nutritional hyperparathyroidism, osteoporosis, and rickets.
What is Metabolic Bone Disease in Reptiles?
Metabolic bone disease is a complex disease. The primary problem is a disruption of calcium metabolism which causes a host of related problems. Due to the importance of calcium in bone formation and muscle function, most of the signs and symptoms are related to bone and muscle development. There is no single cause of MBD and the disease is not as simple as calcium deficiency.
Symptoms of Metabolic Bone Disease in Reptiles
Symptoms of MBD vary depending on the severity and length of time over which the condition has developed. A veterinarian who specializes in reptiles and amphibians will be able to best recognize symptoms of MBD. Symptoms of metabolic bone disease include:
A reptile's legs can become bowed or swollen if it has MBD. Bumps may develop on the long bones of the legs. The bumps are the body's attempt to strengthen the skeletal structure with fibrous tissue to compensate for the lack of calcium in the bones.
A reptile with this symptom will have an arched spine. Or bumps will develop along the bones of the reptile's spine as well as the base, which are other areas of the skeletal structure that the body is trying to strengthen with fibrous tissue.
The bones of the jaw can also become depleted of calcium which will cause it to malfunction. The jaw of a reptile will soften and there may be swelling of the jaw (which is why this disease is sometimes called "rubber jaw"). In addition, the lower jaw of the reptile may recede in response to calcium deficiency.
In turtles, such as yellow-bodied sliders, softening of the carapace or plastron (the shell) occurs with MBD.
MBD results in reptiles developing muscle tremors, jerky movements, or twitching in the muscles of the legs and toes.
The reptile will not be able to eat or drink once the disease affects its jaw and tongue.
MBD causes a reptile to become constipated or experience obstipation (not defecating at all).
MBD causes the bones to break due to bone weakness and lack of calcium.
Reluctance to Move
Weakness, lameness, and even partial paralysis can occur with MBD. The reptile will sometimes be unable to move its legs or lift its body off the ground because of how weak and lethargic it feels. This is also due to the depleted calcium in the reptile's bones.
Causes of Metabolic Bone Disease
Normally, the ratio in a reptile's body of calcium to phosphorus ratio should be around two parts calcium and one part phosphorus (2:1). When the calcium level is relatively low the body tries to compensate by taking calcium from wherever it can, including from the bones. This leads to a softening of the bones making them susceptible to fractures and also leading to a deposition of fibrous tissue as the body tries to strengthen the bone in an absence of available calcium. Calcium also impacts a number of other physiological systems, including muscle contraction and blood clotting.
Therefore the 2:1 ratio of calcium to phosphorus is ideal in your reptile's diet but calcium metabolism is not that simple to fix. Vitamin D (especially D3) is also vital to calcium metabolism and because some reptiles do not absorb vitamin D that well, they need ultraviolet light exposure to manufacture their own vitamin D, further complicating the problem.
Basic factors that can skew the calcium to phosphorus ratio include:
- Too little calcium or too much phosphorus in the diet
- Presence of substances in the diet that impair the absorption of calcium
- Vitamin D deficiency
- Lack of exposure to the UVA and UVB necessary for the reptile to produce its own vitamin D
- Inadequate protein
- Kidney or liver disease
- Small intestinal disease
- Disease of the thyroid or parathyroid glands
- Living in cool temperatures, which impairs digestion and affects calcium absorption
Diagnosing Metabolic Bone Disease in Reptiles
Metabolic bone disease is distinctive enough that a diagnosis is usually made based on the symptoms, physical exam, and a discussion of proper husbandry (meaning the equipment used to care for the reptile and the habitat in which it lives). Radiographs (X-rays) may be taken to confirm the diagnosis and monitor treatment. Calcium levels in the blood may also be tested.
Treatment of MBD depends on the severity of the disease. For very mild cases, a switch to a balanced diet and appropriate husbandry may be enough. Severe cases require intensive calcium and vitamin supplementation as well as an increase in high-intensity UVB rays under an exotics veterinarian's care.
Prognosis for Reptiles with Metabolic Bone Disease
A diagnosis of metabolic bone disease requires timely treatment or the reptile will not survive. The prognosis for reptiles with mild symptoms is positive as treatment is tolerated quite well. Even reptiles with more severe symptoms and treated will make a full recovery. Though it may be difficult, it is not impossible for a reptile with an extreme case of metabolic bone disease to recover with the right treatment.
How to Prevent Metabolic Bone Disease
MBD is almost always a result of poor husbandry but it is also generally preventable by providing a proper environment and diet specifically for your type of reptile. This is not always easy or inexpensive for a reptile owner to do but is vital to the health of all pet reptiles.
Proper husbandry is more than just providing the right diet. The following are important in both the prevention and treatment of metabolic bone disease:
- A diet balanced in calcium and phosphorus, protein, energy, and other reptile-specific nutrients
- Exposure to UVA/UVB invisible light rays
- Proper heat gradients
- Proper light/dark cycles
- Adequate enclosure and/or room to exercise