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).
Diagnosis
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.
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.
Prevention
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.
Lighting
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.
Feeding
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.