Metabolic Bone Disease, Calcium and Vitamin D3


Metaboilic Bone Disease (hypocalcemia ) is defined as "an absolute decrease in total bone mass". In general terms it is the "borrowing" of calcium from the bones to ensure the correct amount is found in the cells and blood. i.e. the bones of the animal are used as a calcium store.
Only 1% of calcium is found outside the bones but this 1% is essential for muscle contraction (such as the heartbeat), nerve function, blood clotting, metabolic functions and enzyme activity.
This removal of calcium from the bones without replacement causes weak and brittle bones and fractures are commonplace. Eventually if the calcium deficit is not reversed the disease is fatal.

MBD is generally caused by insufficient calcium levels (or wrong form of calcium) in the diet, wrong calcium to phosphorus ratio, too much protein in the diet, wrong temperature for digestion, or insufficient UVB to allow synthesis of Vitamin D3 / insufficient vitamin D3 to allow calcium absorption.

Organ dysfunction (Liver and Kidney) is another cause although somewhat rarer than the above.

Another form of hypocalcemia sometimes occurs in gravid female chameleons. When their eggs pass through the shell gland the calcium requirement is too much or too quick to leach from the bones. This is a very serious condition and one which prevention by feeding a gravid female an especially good diet is better than cure. Note the suggestion to feed well rather than supplement. Too much calcium by supplementation can cause egg binding whereas dietary calcium take up tends to be better regulated by the chameleon.



Visual signs



Early signs can be tongue dysfunction and week grip. Pliable, swollen or more rounded jaw bone - the strong muscles of the lower jaw pull the bone round and gives a shorter appearance. Often the jaw is overshot as a result of this.

Limbs are also pliable and/or swollen and may show fractures (often multiple) and/or deformities. Classic signs are the limbs appearing to have an extra joint or irregular swellings. The first is caused by fractures, the second by the body trying to sure up the weakened bone structure with fibrocollagenous connective tissue.

The animal may appear lethargic. Anorexia is common as the jaw becomes too weak to function properly. The animal no longer tries to climb and rests at the bottom of the enclosure. Inability of the limbs to raise the body off the ground is a sign of advanced MBD. The limbs function but without power sufficient to lift or move the body.

Once the calcium levels in the blood drop too low muscle tremors and laboured breathing can be observed. Worryingly it is usually the muscle tremor stage where many keepers notice something is wrong. At this stage "home remedies" should not be tried. A trip to the vets is needed.


If untreated the muscle tremors will eventually lead to cardiac failure and death.



Here is a female Veiled Chameleon with advanced MBD. Note the front legs
are curved. This is caused by multiple breaks. The animal could not support
its own body weight.

Sadly the animal had to be euthanased.


Clinical Tests



X rays can be used to determine bone density and degree of severity of the disease. They can also show if a female is gravid and hence going through the strains of egg production.

Blood serum tests may be miss-leading (often shows all clear) as the reason the calcium is leached from the bone in the first place is to maintain calcium levels within the normal range in the blood (amongst other places).


Calcium / Phosphorous ratio


Phosphorus combines with calcium to form calcium phosphate, which forms the majority of bone in the body.
Ideally a diet should have a calcium:phosphorus ratio of 1:1 to 2:1. Most insects commonly fed to Chameleons are high in phosphorus and low in calcium hence the standard advice that insect prey should regularly be dusted with calcium powder.

Below is a table showing the nutritional contents of commonly available feeder insects kindly supplied by Peregrine Livefoods.

Species
% moisture
% fat
% calcium
% phosphorus
Ca:P ratio
% protein
Mealworm
68
8.5
0.016
0.3
1:19
18.9
Morio 59.8
15.2
0.022
0.21
1:10
19.5
Waxworm
65.1
15.5
0.037
0.19
1:5
15.5
Locust
73.2
5.8
0.035
0.18
1:5
15.9
Banded Cricket
71.8
6.3
0.14
0.22
1:1.5
16.5
Black Cricket
66.7
12.0
0.18
0.22
1:1.2
15.8
Silent Cricket
68.8
9.3
0.17
0.22
1:1.3
16.4
Brown Cricket
70.7
4.4
0.089
0.28
1:3
19.8

Crickets were fed on layers mash and potato. Locusts on cabbage.


Calcium


Chameleons use calcium according to their metabolic rate. Lowland species such as Veileds and Panthers require more calcium than montane species such as Jacksons and Fischers.
This is because their metabolism is faster as they are kept at higher temperatures.
Babies need more calcium than adults and gravid females need more than males.


Supplements and percentage of calcium
Calcium Carbonate 40%
Limestone 38%
Calcium Lactade 18%
Calcium Gluconate 9%
Bone Meal 24% calcium, 12% phosphorus

Interestingly the chameleons body absorbs calcium more easily from low volume calcium supplements.
Hence vets will usually treat MBD with Calcium Gluconate however this is when calcium levels are clinically proven to be low.

For routine supplementation Calcium Carbonate is preferred because it is safe and effective.
Limestone powder is a very good second choice.

Calcium Lactade (sometimes called calcium sugar) is water soluble so can be added to the crickets drinking water to increase their calcium content.

Try to avoid "homemade" supplements such as bonemeal and cuttlefish. These can contain high levels of toxic metals such as lead and mercury. Commercially produced Calcium supplements are usually screened for such toxins.

Hard water (or bottled water with added calcium) helps get additional calcium into chameleons.
Some studies suggest hard water give chameleons more calcium than regular dusting the food with calcium powder.


Good nutrition alone is not enough to prevent or correct MBD



Vitamin D3


Vitamin D3 (a hormone) is needed for calcium absorption in the intestine. The major problem with Vitamin D3 deficiency is, therefore, reduced calcium absorption by the intestines regardless of calcium availability in the diet.
Vitamin D3 starts production in the reptiles body by UVB light reacting with cholesterol in the reptiles skin. This in turn synthesises the production of pre Vitamin D3.
Pre- Vitamin D3 is transferred by the kidneys then the liver into Vitamin D3.

In tests on Panther Chameleons it was shown that dietary D3 is not as easily used by the body as synthesised D3. Therefore supplementation should only ever be used as the name suggests, to supplement good husbandry. i.e. calcium rich diet and sufficient UVB light


Inhibitors of calcium absorption


Temperature
Unless the animal can attain its preferred temperature it will not be able to digest properly which will prevent calcium being absorbed from the diet.

Stress
Stress hormones reduce or shut off the digestive system where calcium is absorbed plus affect the synthesis of Vitamin D3 (another hormone).

Lack of UVB
Old or incorrect UVB lighting.

High protein Diet
Main source of phosphorous is protein so a high protein diet unbalances the Calcium to phosphorous ratio and therefore contributes to MBD

Oxalates
Oxalates found in certain greens such as cabbage, and spinach (commonly used as "gutload") bind with calcium making it unusable so should be avoided. Stick to Spring Greens, water cress or dandelion leaves.

High fat diet
Dietary fat also lowers calcium absorption so feeding waxworms which are high in fat (even when dusted with calcium powder) are not sufficient to replace a calcium deficit.

Dehydration
Healthy kidneys are vital for D3 synthesis. Correct humidity reduces the workload on the kidneys.


If you suspect MBD


Firstly the cause needs to be identified and rectified. More likely to be husbandry.

Climbing perches etc should be removed and wide low perched should be used instead. A more restrictive sized enclosure would again help prevent further damage.
The enclosure should be kept at the upper level of the animals preferred temperature. Humidity should be measured and within preferred levels. Any outside stress factors should be removed. Consideration should be given to moving the enclosure into a quieter room if possible.
Renew the UV bulb and decrease the gap between the reptile and tube.

Veterinary advise should be sought. MBD should not be treated by home remedies. Particularly as some of the symptoms of hypercalcemia (too much calcium) are similar to too little.


High levels of flouride in drinking water


High levels of fluoride found in some tap waters can cause symptoms that mimic the signs of MBD.

If your chameleons are experiencing signs of MBD even though husbandry and nutrition is correct you should check the levels of flouride in the water. Each Water Authority publishes an analysis of their drinking water.
Recommended maximum levels for humans are 1.0 ppm (parts per million) fluoride. Or 1mg per litre. Fluoride has a narrow safety range with 4 ppm posing serious health risks to humans. Although no serious testing of flourosis in chameleons has been done it is suggested that the human limit is probably on the high side.

 

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