Metabolic Bone Disease In Your Iguana
MBD
= Nutritional Secondary Hyperparathyroidism (NSHP)

 

 

 

 

Ron Hines DVM Ph.D.

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Is Metabolic Bone Disease Common In Iguanas ?

A small number of serious problems are common in pet iguanas. In order of frequency, in my practice, they are aggression, metabolic bone disease, low-temperature induced infections, kidney failure, female reproductive problems (eggs, dystocia), urinary stones (cystic calculi), non-food objects swallowed, accidents and shedding abnormalities (Dysecdysis).

It is unfortunate MBD is seen so frequently because it is an entirely preventable disease. It only occurs when owners have not learned the proper diet, temperature and lighting needs of their pets.

What Is Metabolic Bone Disease (MBD) ?

Metabolic Bone Disease does not occur in wild iguanas. The term MBD is used to describe any condition in which the reptile’s bones do not contain enough calcium. It is also called nutritional secondary hyperparathyroidism or NSHP (even though some of the possible causes are not nutritional), fibrous osteodystrophy or hypocalcemia.

What Caused MBD In My Pet ?

Because calcium reaches your pet’s bones through a complex process, veterinarians believe that MBD can occur in several ways. And because the factors involved in bone formation in reptiles are not fully understood, veterinarians and reptile enthusiasts take what we know about bone formation in warm-blooded animals and assume that it applies to reptiles as well. That is why many suggestions as to the possible cause and treatments of MBD in reptiles are based on readings about calcium metabolism in humans and other mammals.

Reptiles developed their bone physiology to suit their cold blooded metabolism 65-251 million years before warm blooded creatures walked this Earth. With time, we will probably learn that reptiles are just too different from mammals for some of these assumptions to be correct.

What we do know is that to have strong bones, your iguana must:

1) Be fed a diet that has adequate calcium
2) Be fed a diet that does not block calcium absorption
3) Be fed a diet in which the amount of calcium is balanced to
the amount of phosphorus in a certain way
4) Produced adequate vitamin D-3 to allow calcium absorption through the intestinal wall
5) Be maintained in a temperature that allows normal body metabolism
6) Have adequate kidney function to prevent calcium loss

What Are The Signs Of MBD In My Iguana ?

Metabolic bone disease is a problem that develops very gradually. Your pet’s skeletal bones loose density (calcium) a little at a time – similar to the x-rays in the illustration at the top of this page. In that illustration, the iguana to the far left has normal bone density and conformation while successive iguana images going right have less and less bone density.

One of the first signs you will see is a gradual rounding of your iguana’s head and receding of its lower jaw in profile. These iguanas often spend their time with their mouths slightly open – quite abnormal for a relaxed pet. Their nose may also turn upward giving them the appearance of “The Creature From the Black Lagoon”.

At the same time, these pets develop a tendency to carry their body lower as they walk and their legs farther out (splayed).

As the decalcification of its skeleton continues, your iguana will have trouble lifting it head and it will develop a “Popeye” appearance to its arms and legs (smaller near the joint – fatter in the middle).

At this stage, the bones of its tail often fracture – giving its tail a crooked profile. At this time too, iguanas with MBD begin to spend more time on the cage floor and less time climbing.

Their joints, leg bones and spine become more lumpy or knobby as their body responds to small spontaneous fractures that occur. Joints are more noticeable as the pets loose weight (fibrous osteodystrophy).

Late in the disease, the iguanas can only slither around because their leg bones have become so distorted and flexible. Some owners describe them as looking like they were made of Jell-O or silicone rubber. When they are willing to walk, these lizards have an abnormal, swaying gait. Iguanas are very resistant to pain – this is due to bone deformity rather than painful lameness.

X-rays may show fractures of the weakened bones of the legs – similar to the right rear leg in the last iguana x-ray image. Pets can also suffer spinal fractures that lead to paralysis, and constipation.

Some of these iguanas twitch and move jerkily – possibly due to low blood calcium. The more advanced the MBD and the darker their environment, the less likely these iguanas are to eat.

Immature iguanas with borderline MBD are often stunted, appearing younger than their true age. This is because mineral deficient diets tend to be deficient in nutrients other than minerals and because the improper husbandry practices that lead to MBD lead to a number of other health issues.

How Will My Veterinarian Know That MBD Is My Iguana’s Problem ?

There are no other conditions that can be confused with a typical advanced case of metabolic bone disease. If your veterinarian suspects an early case, or if the vet wants to rule out MBD as a contributing factor to another illness, the veterinarian will probably suggest an x-ray.

The skeleton appears white on x-rays as the portion of the film where the rays are stopped by the pet’s bone. Your veterinarian has a chart that tells what the proper x-ray strength is for an iguana the size of your pet. When these x-rays pass through your pet too easily, the veterinarian knows that your pet’s bones lack sufficient mineral (calcium phosphate).

Unless the pet is comatose, having tremors or seizures; blood calcium levels are usually not low. Your pet will continue to rob its bone stores of calcium to maintain the calcium level in its blood until very late in the disease.

Are There Treatments That Will Cure Or Help ?

When MBD is detected early, it is quite treatable. However, the majority of cases are brought in to veterinarians much later in the disease when treatment is less successful.

Treatment of MBD is aimed at supplying your pet with added calcium and the vitamin D-3 necessary for the iguana to utilize the calcium.

Rehyration

Sick iguanas do not consume enough water. Iguanas get most or all of their water from the plants they eat and many of these lizards are not eating well. When they do come in for treatment, they are often dehydrated. If the pet is very ill, the best way to restore its fluid balance is by injection of balanced saline solutions. If the pet is still motile and vigorous, the fluids can be given orally through a tube. Owners who have not been instructed in the method, should not attempt to tube feed or hydrate iguanas unassisted. It is too easy to injure the mouth or to have the pet swallow the tube when it is done orally or to give fluids too quickly, in too large an amount, at an incorrect temperature when they are injected.

Tube Feeding

There are risks in tube feeding as well. Iguanas do not cooperate with this procedure and in the process of prying its mouth open, the lips and teeth are often injured or the jaw broken. So first attempt to present green leafy vegetables in various ways to tempt your pet. Increase the amount of natural and artificial light falling on the food, present it in several bowels or dishes, mist it with water and raise its cage temperature to about 88F if it is low.

If your pet still refuses to eat, it will need to be tube fed. It is convenient to use strained human baby vegetables, but strained baby vegetables may have too much fat and insufficient fiber and calcium content. A better way is to prepare a blended combination of greens and water. Begin with a minced variety of greens that include at least three of the greens I suggest as your iguanas maintenance diet. Blend them to a soupy consistency. Tube feeding is best done at an animal hospital that is experienced with reptiles. An alternative is to seek instruction from the herpetologist at your local zoo. It is much safer to give small amounts frequently rather than large amounts infrequently. I like to massage these pet's tummies for a while after the feedings.

Change to a calcium-rich diet

Your iguana developed MBD because it was not eating the right things and/or because it didn’t get enough natural sunlight. As you surf the Internet, you will see a great deal of conflicting advice as to what you should feed your iguana. Remember that none of the ingredients available to you in the US or Europe are the natural diet of iguanas. The best advice I can give you is to offer your iguana only a wide variety of green, leafy vegetables. In offering variety, you are most likely to satisfy all of your iguana’s nutritional needs. These diets do not need to be “balanced” as we tend to think of them for humans. That is because iguanas use a complex mixture (flora) of living bacteria and protozoa in their intestinal tract to produce all the nutrients their bodies need. These are not the organisms found in “probiotics” or yogurt. Baby iguanas are believed to obtain these healthy intestinal bacteria and protozoa by eating the feces of mature iguanas.

The diet you feed your iguana should consist of the leaves and stems of many edible green plants. The greater the variety of plants ingredients, the more likely it is that your iguana will remain healthy or overcome early MBD. Your iguana will remain healthy if its diet is made up of some of the following plants:

Kale, collard greens, escarole, turnip tops, beet greens, mustard greens, dandelion, Chinese cabbage (bok choy), Swiss chard, hibiscus flowers, endive, sprouts, arugula, green cabbage.

This is only a partial list. Basically, feed only items that are the leaves or tops of edible plants you find in the supermarket. Here in Brownsville, Texas, our local population of wild iguanas thrive on a diet of hibiscus flowers. If you live in a tropical area, adding these flowers is fine. Wash everything very well and dice them up in a salad. Replace the salad daily.

Are There Plants And Vegetables And Other Things I Should Not Feed My Iguana ?

Iguana enthusiasts avoid feeding certain plants to their pets. These decisions are based on theoretical knowledge regarding compounds known to exist in certain plants. Spinach, cabbage and beet tops, as well as some other high-oxalate plants are frowned upon by many enthusiasts because the oxalates they contain might conceivably interfere with calcium absorption. I do not know of any cases of MBD that occurred solely due to the feeding of these plants. I believe your pet will be safe if you simply offer it a great variety of greens.

There are so many potential vegetables and plant out there so suggestions on what to feed iguanas vary a lot. Basically, you should aim at a diet with a large variety of plant ingredients that is low in fruit sugar, low in protein, rich in calcium and which promote good digestive tract function.

Reptiles that consume cat or dog food or other high protein things like eggs, peas and beans often go on to develop kidney problems (gout). Peas and beans are also high in phytic acid. There are no studies I know of on the effects of phytic acid on iguanas - but in other plant-eating reptiles they are converted to oxalic acid which blocks the calcium absorption so necessary to prevent MBD.

Lots of supermarket fruit are too high in sugar and too low in fiber. I would not provide them to your iguana in any substantial amounts. The same goes for root vegetables.

What About Feeding Other Stuff My Iguana Likes ?

The organisms in your iguana’s intestinal tract will not thrive when they are exposed to the high sugar levels of fruit, the high carbohydrate levels of pasta and starchy vegetables or the high protein content of insects, human or pet foods. In the open tropical landscapes of Central America and South America where iguana’s live, energy-rich, nutrient rich foods are not what they normally eat. They have adapted to thrive on high-fiber, low nutrient food sources. They may enjoy eating other stuff – but their health will suffer in the end if it makes up a substantial portion of their diet. Remember, you are not feeding your iguana, you are feeding a whole zoo of microorganisms that live in your iguana’s body. It is those organisms that will be responsible for maintaining your pet’s health.

Supplemental calcium

The green leafy vegetables I have mentioned are very high in calcium. They do not have high phosphorus levels that might interfere with calcium absorption. If you feed your iguana a diet of green, leafy vegetables, it needs no calcium supplementation.

If, however, your pet has already developed MBD, added calcium may help. If the pet is not eating, the best source of calcium in iguanas that must be force-fed is oral calcium glubionate (Neo-Calglucon). If the pet is still eating, crushed calcium tablets can be sprinkled on its food. Whatever calcium source you use, be sure it does not contain vitamin D (colicalciferol). Too much vitamin D is toxic.

Calcium injections should be reserved for severely ill animals. When calcium is given orally, the iguana’s body can decide how much needs to be absorbed. But when it injected, all of the calcium enters its circulation. We have no way of safely and reliably calculating how much calcium should be injected. If too much is injected, fatal complications can occur.

A sign of low blood calcium in iguanas suffering from MBD are muscle tremors. In these pets, or pets in very advanced stages of bone decalcification, your veterinarian may decide that the pet does not have the time or remaining capacity to absorb oral calcium. In these iguanas calcium gluconate injections are warranted and can be life saving.

Breeding female iguanas may need extra calcium to form eggshells. On a diet of green leafy vegetables and full-spectrum lighting, they should have plenty of calcium reserves and no additional calcium should be needed. But if you are uncertain, you can add some to the diet of your breeding-age female iguanas.

Supplemental Vitamin D-3 ?

I try to write these articles in a way that is brief and easy to understand. That can not be done when discussing vitamin D-3 and iguanas. Rest assured that the most educated herpetologists are as confused as the rest of us when it comes to vitamin D-3 metabolism in reptiles.

We know that Vitamin D-3 (cholecalciferol, calcitriol) is required for iguanas to absorb calcium from their food.

Wild iguanas are strictly plant eaters. Some nutritionists doubt that iguanas have the ability to utilize the vitamin D-3 present in their diet or supplements or to sustain their vitamin D-3 levels through injection or oral supplements. Diets with as much as 3,000 IU vitamin D3/kg did not prevent bone fractures and cortical bone thinning in green iguanas.

But others believe that iguanas can utilize dietary vitamin D-3 supplements. A study conducted at Central Michigan University indicated that iguanas might be able to utilize D-3 supplements. However, the study only lasted 6 month; and with a half-life of 2 months or more, the iguana's vitamin D-3 levels could have been adequate throughout the length of the study - even if they absorbed no D-3 from their diet.

Another hint that iguanas might be able to utilize vitamin D supplements comes from another iguanid lizard, the Chuckawalla, that lives in the Desert Southwest. Richard Montanucci, biology professor at Clemson University, kept a colony of these lizards from 1992 - 2006. During that period, the reptiles received minimal outdoor sunlight and no artificial UV light source - just "ordinary incandescent lights (GE BR40 Floodlights )". They were fed a mixture of green beans, romaine lettuce and dandelion, supplemented with a 50:50 mixture of Rep-Cal and Herptivite - less than 1/8 tsp over 2/3 cup of greens. These lizards had normal reproduction, nearly all their eggs were fertile, their young developed normally and several grew up to reproduced successfully themselves. GE makes several floodlights in their BR40 line. I am unable to confirm which ones were used, other than that they came from Ace Hardware. Shatterproof GE bulbs were, at one time, coated with Teflon which caused display bird mortality at the San Antonio Zoo. Be sure not to use teflon coated bulbs.

We do know that Iguanas have the ability to produce all the vitamin D-3 their bodies needs when they are exposed to sufficient natural sunlight or artificial light that contains ultraviolet B radiation and that their natural diet in the wild does not contain significant vitamin D3.

Just as injectable calcium, injectable vitamin D-3 should be reserved for heroic efforts to save iguanas in the last stages of MBD when they unlikely to survive or self-feed. To date, improvements after administration of D3 have not been dramatic.

Calcitonin

Some veterinarians treating severe MBD with Calcitonin . Calcitonin is a hormone that is involved in regulating calcium metabolism within the body. Whereas hormone produced in the parathyroid gland of mammals (PTH) moves calcium out of the bones and into the blood, calcitonin has the opposite effect. Very little is actually known about the effect of administering this hormone to reptiles. In humans, it has been suggested for osteoporosis and to lower abnormally high calcium blood levels.

If it is given to iguanas, blood calcium levels need to be carefully monitored to be sure they do not drop too low. Some veterinarians have found that administering calcitonin derived from Salmon (miacalcin) appeared to speed the healing of bone fractures associated with MBD.

Full-spectrum lighting and UVB

Sunlight is made up of all the visible wave lengths ranging from 380 to 750 nanometers. When all the wavelengths are present, the light is often called “ full spectrum”. For iguanas to produce their own vitamin D-3, they need to be exposed to enough of the shorter wavelengths (ultra violet B = UVB). These are waves in the 280 – 315 range. When these wavelengths are present in sufficient quantity, the iguana produces its own vitamin D in its skin.

The best source of these wavelengths by far is exposure to natural sunshine. In the wild, in tropical climes, this is not a problem. But indoors, in northern latitudes where iguanas are kept as pets, it can be. Not as much sun shines in the Northern United States. And when the sun must pass through window glass, clear plastic, or terrarium walls, much of the important UVB rays are lost.

The solution to this problem is to provide your iguana with an artificial source of UVB rays. Many companies market these lamps. All claim that their product is undoubtedly the best.

Inexpensive UV reptile lamps need to be changed every 4-6 months. These bulbs continue to produce light long after the amount of UVB rays become to low. Westron claims their Mega-Ray EB60 lasts 18 months - but manufacturers products do not always live up to their claims and UV bulbs are no exception.

Be sure the iguana can get 6-12 inches close to most of these bulbs but be just as sure it can move away when it wants to so it does not get burned. Wild Iguanas regulate their body temperature and exposure to UVB rays closely by basking in different areas of sun and shade. You must permit your pet iguana do do the same thing. It will innately know how close to the lamp it should be and for how long it should be exposed. For the most detailed, non-biased information on UVB lamps, visit UV Guide UK.

Two popular bulb brands in the US are ZooMed’s Reptisun and T-Rex, manufactured by Westron. My preference is for screw-in mercury vapor UVB bulbs over fluorescent types. However, some of these bulbs have been so powerful as to cause eye injury and sunburn. Be sure that your iguana can move far enough away from these powerful light sources when it desires to do so and check the manufacturers suggestions as to distance to the cage, etc.

Compact meters are available to test the amount of UVB rays these bulbs are producing. (Solarmeter model 6.4). This is a great investment for serious hobbyists. If your veterinarian has a serious "herp" interest , he/she should own one and should let you borrow it.

Some of the screw-in types also produce warmth, which can be very beneficial in cold climates.

Light sources that produce the longer UVA wavelengths are also important for your iguana to perceive color. Lamps that produce primarily UVB light do not illuminate your iguana’s habitat sufficiently on their own. Your iguana needs plenty of the other wavelengths to feed and to interact normally with environment. So be sure that the general daytime level of illumination where your iguana lives is sufficient. If house plants do not thrive in the level of light that is present, your iguana will not either.

A low-tech method, whose accuracy I cannot vouch for, is to place a strip of white high-lignin paper (eg newspaper) in the habitat and note the degree of yellowing over a few days. Yellowing occurs when high-lignin paper is exposed to UV rays in the 250-400 range – the same range that seems to benefit iguanas. However, the super high-tech method is to utilize vitamin D conversion ampoules – something a casual pet iguana owner is most unlikely to do.

Proper temperature (thermoregulation)

All of your iguana’s metabolic processes rely on a proper body temperature. Iguanas that are too cold do not digest their food well and become more susceptible to infections. They also loose much of their ability to synthesize vitamin D3. Inversely, iguanas that are kept too hot will not do well either.

So it is important that you establish a heat gradient for your pet. Using heating lamps specifically designed for reptiles and under-the-habitat heating pads designed for reptiles, establish one end of the pet’s habitat that remains at about 96F and gradually declines to 85F at the far end.

In this way, your iguana can choose the temperature that suits it best. Sick iguanas need to be closely monitored because they cannot move well and can be sun burnt or overheated easily.

Two or three reptile thermometers need to be placed inside the habitat to keep track of the temperature. Be sure the iguana cannot eat them.

Fracture repair

Iguanas with Metabolic Bone Disease tend to suffer fractures of their legs, spine and tail. The tail fractures are not important; but leg fractures should be immobilized to heal in as correct an alignment as possible. The abnormally soft bone of MBD does not lend itself to complicated orthopedic surgery. But an external brace made of surgical tape, reinforced with pipe cleaners works well when it is combined with a return to good nutrition, temperature and UV light exposure.

Spinal fractures, that result from MBD often lead to hind leg paralysis and constipation. The constipation can be managed with enemas. But paralyzed pets will need help moving to control their body temperature and to feed. Miraculously, it is not uncommon for paralyzed iguanas to regain leg function once their MBD has been corrected.

Housing modification

You will need to put thought into modifying your iguana’s habitat to make it as easy as possible for it to move about to feed and control its body temperature and light exposure.

Bisphosphonates

Some iguana interest groups have discussed the possibility of administering bisphosphonate class medications to iguanas with MBD. Fosamax, Reclast and Boniva are drugs in this class that you know.

These medications work well to slow bone loss when dietary calcium and body vitamin D-3 sores are adequate. But this is not the case in MBD. My concern is that these medications might lead to a fatal drop in circulating blood calcium levels in the iguana similar to what they occasionally cause in humans. . Kidney damage is known to slow their excretion and kidney damage is common in iguanas that have been fed an improper diet.

Does My Iguana Need A Vitamin/Mineral Supplement ?

If iguanas receive a proper diet and sufficient UVB light exposure, they do not need a vitamin or mineral supplement.

Many iguana supplements are on the market - but since the vitamin needs of iguanas are unknown, I do not know how these companies made their decisions as to what to put into the bottle. Often, when a reptile’s vitamin and mineral requirements are unknown, manufacturers look for something similar to use as a basis. I assume that most of these formulations are based on the requirements of poultry. Companies also tend to low-ball the amount of A and D in these preparations because they know high levels can be toxic and go with high levels of C, E and B vitamins because these are not toxic.

If you give your iguana too much of a supplement containing vitamin D, it may be susceptible to calcium deposits in abnormal areas of its body. We think that excessive vitamin D levels in cat and dog foods fed to iguanas has been responsible for kidney damage (metastatic calcification).

Supplements also contain vitamin A. At too high a level, vitamin A can cause liver damage. Your iguana receives all the vitamin A it needs as the beta-carotenes in the green leafy plants it should be eating. If Iguanas function as other animals do, these carotene pigments are converted to vitamin A by the organisms living in its intestine as well as by its own liver.

Should I Be Concerned With The Mineral balance In My Pet’s Diet ?

Your iguana needs a steady source of calcium in its diet.

Its ability to utilize dietary calcium is also influenced by the amount of phosphorus in its diet (optimum = 1.2:1 ratio). If you feed a large variety of green leafy plants to your iguana, the calcium to phosphorus ratio in its diet will be fine.

If your iguana does not receive sufficient new calcium, it will remove it from its bones to maintain normal calcium blood levels. This is one cause of MBD.

The iguana’s kidneys are responsible for removing excess phosphorus from the body. If your pet has kidney disease (gout), its requirements for dietary calcium may increase. Most of your iguana’s calcium loss is through its kidneys as well. That said, blood calcium levels in iguanas with kidney failure are often too high.

Perhaps, breeding age female iguanas need more dietary calcium to produce their eggs. Calcium, given alone, is not a toxic element. So there is no harm in giving a modest calcium supplement (top dressing) to breeding females.

Kidney Disease And Metabolic Bone Disease

Kidney damage is a common problem in middle age and older iguanas fed an improper diet. When it occurs, it causes a condition called gout and renal secondary hyperparathyroidism that can be a factor contributing to MBD. This problem leads to elevated levels of phosphorus in the animals blood which also contribute to MBD.

Feeding diets high in animal protein, over supplementation and even insufficient humidity have all been suggested as contributing to this problem.

With Conflicting Ideas On How To Prevent MBD What Can I DO To Prevent It ?

There are volumes of information on the Web regarding UV light sources and reptile vitamin supplements. However, very little of it is based on hard data or scientific evidence. Because we do not know how much vitamin D-3 should be added to their diets or if they can even utilize it and because so little is known about their optimum artificial light source needs, the best way to judge if your pet is safe from MBD is to have its blood vitamin D-3 level measured.

The test used to measure blood vitamin D-3 is the 25 hydroxycholecalciferol assay. In 2009, the only laboratory that I know of that runs this test is the Michigan State University Diagnostic Center

The test can be run on as little as 75 microleters (0.075ml) of blood serum. Normal values to date at this lab, seem to run between 50 and 275 nmol/L with some running as high as 400. Whereas iguanas with MBD run as low as 13nmol/L. Assays done at other laboratories reported normals of 365 and 51-393.

As more iguana blood samples are run at this lab, the interpretation of what constitutes normal and abnormal values will become more apparent. The current cost of the test is $31.