Metabolic Bone Disease
There are a variety of metabolic bone diseases that result in deformities of the skeleton in captive reptiles. The most common form of metabolic bone disease seen in captive reptiles and amphibians is nutritional secondary hyperparathyroidism (NSHP). NSHP is caused by not eating enough calcium or having too much phosphorus in the diet and/or a lack of vitamin D3, and inadequate exposure to ultraviolet (UVB) light.
The low levels of calcium in the diet cause the parathyroid gland to produce too much parathyroid hormone. This hormone causes the body to remove calcium from the bones, which eventually results in the disease. Because the bones do not have enough calcium, they can become soft or rubbery in some cases and so the disease is often called rubber jaw.
NSHP can occur in all kinds of reptiles and amphibians but is most commonly seen in lizards, turtles and tortoises; a high percentage of cases are seen in young animals due to the higher need for calcium for bone growth, and in female animals due to the increased demand for calcium during the breeding season. The two groups of reptiles and amphibians that get NSHP the most are plant-eating species (iguanas, tortoises) and insect-eating species (bearded dragons, water dragons, leopard geckos), due to the difficulty in balancing these diets for calcium and phosphorus content.
Reptiles and amphibians with NSHP can show different signs of the disease and they often have more than one sign. The most common signs seen are:
- Swollen hind legs (look muscular and are hard to the touch).
- Broken bones misshaped shells in turtles and tortoises (often looks like the shell is too small for the animal or is curved).
- Spinal deviations (kinking, curvatures, bumps) and a kinked tail.
- Problems lifting the body and/or tail off the ground when walking (swimming movement).
- Jerky movements of the limbs and head (tremors and seizures) especially during handling, and the legs may seem paralyzed or weak.
- Another very common sign of NSHP in lizards is a swollen or rubbery jaw and droopy lips that expose the gums.
- In chameleons, the tongue will often not work properly or will hang from the mouth, and they are unable to eat.
Because calcium is needed for muscles to work well, other signs that an animal may have NSHP are problems with egg-laying, constipation, not wanting to eat or problems eating, lethargy (sleeping a lot), small for their age (stunted), bloating, and prolapses (organs protruding from the anus).
Your veterinarian will start by taking a detailed history concerning diet and husbandry and will perform a physical examination. In many cases a diagnosis is made with this dietary and husbandry information combined with the physical exam findings. Your animal may also have blood taken for a complete blood count and biochemistry panel to check for levels of calcium and phosphorus. In addition, X-rays, may be taken to look at the bones. These X-rays are also the starting point for your veterinarian to determine how well your animal is responding to treatment.
The majority of reptiles and amphibians respond well to treatment for NSHP. Treatment will depend on what your animal needs based on the physical exam.
Your animal will often be warmed up so that treatments given are effective. Fluids may be provided for dehydration; if the animal experiences tremors or seizures calcium will be given immediately by injection. After the injection, a liquid calcium supplement will be provided to be given at home and a vitamin D3 injection may be given. Oral calcium should be continued for a period of one to three months or longer.
If the X-rays show that there are broken bones, your veterinarian will discuss treatment options with you. In small lizards and turtles these are often treated with cage rest or tape splints. Your veterinarian will likely recommend minimal handling and lowering or removing climbing branches in the cage to avoid fracturing weak bones. If your animal has constipation, warm water soaks or a warm water enema and gentle massage and manipulation to help with a bowel movement may be recommended.
During this initial treatment period and beyond your veterinarian will discuss proper husbandry needs (see prevention below) such as the provision of adequate temperatures to allow absorption of oral medications. If the patient is not feeding voluntarily, gentle assist feeding, syringe feeding or tube feeding may be initiated. Remember that treatment for NSHP can be lengthy, over weeks to months to correct deficiencies of calcium and/or vitamin D3.
Your veterinarian will monitor how your animal is healing with regular checkups during the first few weeks of treatment; these rechecks are very important to ensure a positive response to therapy. Recheck X-rays are often taken can be useful to evaluate the bone healing process.
The vast majority of cases respond very well to the treatments outlined above but in some severe cases your veterinarian may use calcitonin. Calcitonin causes the calcium in the blood to go into the weak bones. With the use of calcitonin, bone repair may occur as early as two to three months as compared to four to six months without its use.
It is important to remember that after treatment, when the bones are normal again, any jaw problems (overbites or underbites) or spinal curvatures will remain. Gum exposure due to this can be managed with gentle cleaning and the application of a wax lip balm product to protect exposed tissue.
Give treatments exactly how your veterinarian prescribes them. Excessive levels of dietary or supplemental vitamin D3 may be toxic. This occurs most often when supplements with vitamin D3 are provided to animals that are being kept outdoors with exposure to natural sunlight. For animals kept outdoors supplements without vitamin D3 should be used. Although not well reported in reptiles and amphibians, excessive calcium and phosphorus in the diet may interfere with gastrointestinal absorption of minerals such as zinc, copper and iodine, which could lead to deficiencies in these minerals.
In most cases of NSHP, there is a history of poor husbandry that includes feeding a diet low in calcium or high in phosphorus, little or no use of calcium and vitamin D supplements, inadequate exposure to unfiltered sunlight or ultraviolet light, improper temperatures for basking or competition from cage mates for basking areas. Your veterinarian will discuss proper husbandry during your visit but some general recommendations are outlined here.
You can help your pet produce its own vitamin D3 by providing UVB exposure. Unfiltered sunlight is best, but if this is not feasible, full spectrum lighting is needed. Exposure times to UVB light may vary for different species but the usual exposure time is 10 to 12 hours per day. For some species, such as bearded dragons and Leopard geckos, studies have shown they may need as little as three hours per day to maintain vitamin D3 levels and healthy bones.
Light fixtures should be positioned no more than 12 to 16 inches above the basking surface for most types bulbs. However, some, like ZooMed’s high output (HO) fluorescent tubes can be up to 30 inches away. UVB bulbs should be changed every 12 months to maintain adequate UVB output.
General dietary recommendations for avoiding NSHP include:
For those species that are insect eaters, use a process called gut loading. Feed the insects a balanced diet (brand name dry dog food, balanced cricket food, dark leafy greens) shortly prior to feeding to the reptile or amphibian.
Place the insects to be fed in a bag with a calcium supplement, or if kept inside, with a calcium/vitamin D3 combination; then immediately before feeding, shake them up a little to cover them in the supplement, which is known as dusting. Dusting is a very unscientific method of supplementing the diet but has historically been successful. Dust two to three times per week.
For plant-eating species, feed vegetables with a good calcium-to-phosphorus ratio. Examples include: collard greens, endive, parsley, and dandelion greens. For the majority of plant eaters, minimize fruit (no more than 10 percent of total diet) because of its high moisture content, low fiber and sugars that can cause gas build-up. Grass hays should make up a large portion of the diet in many tortoise species (e.g., Russian tortoises). Salads must be supplemented with a calcium supplement such as calcium carbonate; 1g (half a teaspoon) per 100 g of food, given two to three times per week.
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