Metabolic Bone Disease (MBD)
Causes, symptoms and cures
X-ray of a Leopard gecko showing an extremely curved spine as a result of metabolic bone disease. The gecko in question was forced to walk resting upon its forelegs as a result of the deformation. Image kindly supplied by Saedcantas
The same gecko under normal vision showing the highly curved spine. Notice the stumpy (missing) toes, Metabolic Bone Disease (MBD) is sadly often associated with other signs of poor husbandary too. Image kindly supplied by Saedcantas
Metabolic bone disease (the infamous MBD) has been a major issue in herpetoculture from the very start. Despite the standard of technology included in modern vivariums, MBD is still a term that strikes fear into the hearts of lizard keepers. It is always caused by ignorance on the keepers’ part and almost definitely doesn’t occur in the wild. It was commonly seen in Green iguanas Iguana iguana due to their popularity and relatively specialised care requirements. Metabolic bone disease is actually an umbrella term that can refer to any one of the following:
A condition where calcium is mobilized from the bones. The reptiles’ body then forms a build up of tough fibrous tissue to try to reinforce the bone, in the absence of calcium. This is commonly seen in the jaw bones where the muscles continue to pull on the weakened bones, creating a distinctive bowed shape and in some species e.g Green iguanas it can create a rounded, juvenile appearance to the head. This affects the animal’s ability to feed and in advanced cases force feeding via a syringe is required. Areas of hard tissues that result from this condition may appear healthy e.g in the thigh or tail and the owner may well mistake it for muscle, whereas in truth the bones will be highly susceptible to fractures which may not be detected under the tissue layer.
This can be caused by dietary deficiencies (including protein deficiency) but also by lack of exercise e.g no climbing areas for arboreal lizards, inadequate floor space for terrestrial species and also if a limb has been attached to a splint due to a previous fracture. As in humans, it results in thinner, lighter bones due to less calcium being deposited in the bones than is reabsorbed into the blood.
Affects young reptiles. Can result in severely bowed bones (especially the longer bones). Caused by inadequate calcium or vitamin D.
Lower bone density caused by decreased mineralization which is a result of improper calcium: phosphorous ratio. Results in softening of the bones.
Secondary nutritional hyperparathyroidism
Parathyroid hormone or PTH is a hormone that stimulates the bones to release calcium and phosphorous and also stimulates increased absorption of calcium in the digestive tract. This hormone is produced in greater quantities at low levels of serum calcium. Can cause the previous two conditions in young and adult reptiles respectively.
Symptoms of Metabolic Bone Disease
- Bowed legs
- Any areas that appear swollen (especially the jaws and thighs)
- Broken bones
- Difficulty moving, climbing, jumping
- Difficulty holding body off the floor (note some saxicolous (rock dwelling) species don’t hold their bodies far off the floor for any amount of time Laudakia and many other agamids from arid areas and Petrosaurus are only two of the many genera that this applies to)
- Difficulty eating
- General deformations
- Softened plastron/ carapace in chelonians
- In advanced cases partial paralysis e.g the reptile drags its hindlegs and tail
The above image shows a leopard gecko with metabolic bone disease, the main deformation is seen in the jaw, however the front legs show disfigurement too. Image kindly supplied by Molly75
Causes of Metabolic Bone Disease
All of the conditions that fall under Metabolic Bone Disease have effectively, the same outcome: weakened bones by affecting calcium metabolism. The causative agent can be almost any element of husbandry error for the purpose of this guide it will be divided into two main areas: diet and environment both of which should be under the control of the keeper.
Metabolic Bone Disease can be brought on by incorrect diets. It is almost unheard of in snakes due to them consuming whole prey (including the bones which provide adequate calcium). The author has only heard of one case of MBD in snakes: a juvenile grass snake that was kept in a pet shop under poor conditions and fed only mealworms (without supplements). The snake developed kinks and bulges but was eventually rescued by a knowledgeable keeper who nursed it back to health. In lizards both herbivorous and insectivorous it is unfortunately much more common. Insectivorous lizards are often only fed one or two different prey items (crickets and mealworms most commonly) and those are the most readily available and cheapest. This isn’t a balanced diet and any deficiencies in individual feeder insect species are quickly manifested in the reptile. Gut loading is a process where feeders are fed a highly nutritious diet e.g dandelions for high calcium content and then fed to the reptile. This can greatly improve the calcium: phosphorous ratio of all the commonly available feeders and so is greatly encouraged (as long as the bugs are fed the right food. Feed high calcium content food to make up for the natural imbalance in the feeders).
An X-ray of a healthy crested gecko. Notice how white the bone are, the whiter the bones the more dense and/or larger they are, density is a good indication of bone strength. Also take note of the 'calcium sacks' in the head, these are the two large white blotches. The gecko uses these to store calcium. Image kindly supplied by fuzzielady
In contrast to the above this crested gecko shows fairly extensive signs of MBD. Notice how much lighter the white colouration is; the bones simply aren't nearly as dense or strong. Also notice the size of the calcium sacks, they are tiny by comparison. Image kindly supplied by fuzzielady
These make up for deficiencies in the reptile’s food. They are recommended for all reptiles and are especially advised for gravid females and juveniles. They can be mixtures of elements or compounds or just one e.g calcium carbonate, the most common calcium supplement. Please note however that over supplementation can have the same negative effects and be just as dangerous as deficiencies. Always follow the guidelines on the packet, veterinary advice and store correctly (in a cool place ideally a cupboard). Supplements do have use by dates which shouldn’t be exceeded. Note that experts claim in some of the tropical Asian agamids notably the genera Acanthosaura and Gonocephalus cannot tolerate calcium lactate in their drinking water once they reach adulthood and that many of the true chameleons are especially sensitive to over supplementation.
The most widely used livefood due to availability, cost and ease of breeding. Additionally they are accepted by most insectivorous species. Unfortunately adult brown crickets are reported to have a calcium: phosphorous ratio of around 1:6 which is very far from the recommended 2:1. This can be remedied somewhat by feeding high calcium diets to gutload them, however is still won’t achieve a 2:1 ratio so supplementing is still required. Diets shouldn’t consist of solely crickets but they can be included in a balanced diet.
Mealworms Tenebrius molitor
Another very popular food source for reptiles. The larval form of mealworms i.e. the ‘worm’ have even worse ratios than crickets at 1:7. Adults (beetles) and pupae are again, worse at 1:11 and 1:10 respectively. They are also notorious for a high chitin content (which under sub optimal heating the reptiles will excrete, being unable to digest it). An ideal diet should only have a small proportion of mealworms included due to their disadvantages and very undesirable calcium: phosphorous ratio.
Popular as they build on what has made the cricket so widely used without some of the disadvantages and only a few of their drawbacks. They can’t bite reptiles which has been attributed to crickets and are diurnal which is obviously an advantage when feeding diurnal lizards. At around 1:5 their ratio is a little better than crickets but due to how quickly they can eat vegetation they are easier to gutload with fresh leaves and so this ratio can be significantly improved upon but again supplementation will be required. Unfortunately due to their requirement for high temperatures and being harder to breed than crickets they cost more. A diet can be based upon locusts with gutloading and supplementation but again, shouldn’t be made up of them solely.
Morio worms Zoophobus morio
Appearance wise they are similar to a large mealworm. They don’t contain as much chitin as mealworms (in terms of percent) and are very high in protein but are too big for many species and are more difficult to breed than mealworms. They are nonetheless a popular feeder species and, with gutloading, their 1:4 ratio can be improved to 1:1 or even higher (around 1.1:1). Bearing this in mind and the fact that they are relished by most reptiles, the author recommends morio worms to be included to some degree in any insectivorous diet, assuming the reptile is large enough.
A balanced diet, along with awareness of appropriate supplements and an understanding of the signs and symptoms of MBD is essential to tackle it.. Image by brian.gratwicke
They will always have a stigma attached to them but are becoming more popular recently and rightly so. The most popular species in the UK is Blaptica dubia; the dubia or orange-spotted cockroach. They have a low chitin content, can’t fly or climb well, are high in protein and are very easy to breed. They remain expensive due to the demand and so the author encourages hobbyists to start their own breeding colonies. They have a ratio of 1:2.5 which is the best of any of the most commonly offered feeder species and can be easily gutloaded to achieve a better ratio. It is therefore recommended that they are included in any insectivorous lizard’s diet and like locusts and crickets can form the bulk of a balanced diet but supplementation will be required.
Other feeder species
Some other species worth noting are waxworms (larvae of the waxmoth) which have a similar ratio to crickets but are very fatty (too much fat can affect calcium metabolism). They still have their place in a balanced diet and are especially useful when trying to increase the weight of a reptile notably breeding females or underfed specimens. They are very eagerly accepted by almost all insectivorous lizards which makes them very useful for supplementing reluctant feeders as a last resort.
Fruit flies are commonly used as food for hatchling chameleons, agamids and frog species. However a ratio of 1:10 mean they require heavy supplementation but this generally isn’t an issue as hatchlings should have more heavily supplemented diets than adults.
Earthworms have a very desirable 2:1 calcium: phosphorous but aren’t always accepted by many species (exceptions include many of the arboreal, tropical agamids and several skink species including the popular blue tongued skinks Tiliqua).
Butterworms have very high calcium and fat contents and are accepted by anything that will eat waxworms. These are highly recommended but in moderation to avoid over feeding. They are however expensive and cannot be bred due to them being irradiated when exported from their native Chile. They larval stage of a species of Chilean moth that is considered a destructive pest in its homeland. They are likely to remain an expensive, calcium rich treat unless anybody manages to breed them outside Chile.
Phoenix/calci worms are the larval stage of a black soldier fly that can be bred in the UK. They are very high in calcium like butterworms but aren’t as fatty and are more readily available. They are however smaller and aren’t as readily accepted by some species. If possible, they should be included in the diet.
Silkworms are the larval stages of various moth species with the most often seen being Bombyx mori. There is a strong demand for silkworms with breeders always selling out quickly, partly due to the fact that they are notoriously difficult to breed for the average herpetoculturist on a small scale and also due to their excellent nutritional value. They offer a good ratio of nearly 1:1 and also have twice as much protein as fat and contain enzymes thought to be beneficial to health. They are considered by many to be the ideal livefood for reptiles and so are recommended as a large part of an insectivore’s diet where available.
Keepers of herbivorous reptiles do not have the luxury of gutloading and so must be especially careful to get a balanced diet of plant matter. Generally speaking, dark leaved greens are the highest in calcium with collards having a ratio of around 14.5:1 and spinach and mustard having around 7:1. Some poor ratios are also present as in the case of most fruit, carrots at around 0.6:1 and alfalfa sprouts contain even less calcium compared to phosphorous. Please note that despite the dark leaved greens containing high levels of calcium they shouldn’t automatically form the bulk of a diet but should be included along with grasses (which most herbivorous reptiles would encounter in the wild more than fruit or vegetables) and smaller amounts of other plants. Spinach in particular may contain a great deal of calcium but also binds to it, resulting in decreased absorption and so should be avoided as the net gain of calcium is inferior to that from other plants. If a herbivorous reptile shows a particular fondness to a food that is low in calcium it shouldn’t be fed as a majority foodstuff or should be blended in small amounts with other plant matter. Supplementation designed for use on insects shouldn’t be used with herbivorous species unless it is pure calcium carbonate but supplementation for herbivorous species isn’t entirely necessary if a diet is designed carefully.
Inadequate heating and UV lighting both affect calcium uptake. Suboptimal temperatures don’t allow reptiles to digest their food properly and so calcium isn’t extracted from the diet. Research the origins of reptiles to provide a correct temperature gradient.
Ultra Violet lighting is being improved at a rapid rate and is the major technological advantage current reptile hobbyists have over the pioneers of the hobby. A reptile’s skin relies on sunlight (Or in a vivarium artificial light) to manufacture Vitamin D3. This vitamin regulates how the reptile’s body utilises calcium and also how much it absorbs from the diet. Without it, inadequate calcium is absorbed and in most reptile’s cases their health deteriorates quickly. The notable exceptions to this rule, as previously mentioned, are snakes, which is partly the reason so few cases of MBD in snakes are seen. Despite claims to the contrary for years (probably to save money) from hobbyists many expert gecko breeders are now coming to the conclusion that even nocturnal gecko species (including the ever popular leopard geckos) benefit to some degree from UV lighting in the day. Again, research is required to obtain the right percentages of UVB and UVA from a bulb for a species but generally bulbs that display percentages below 5% are better suited for rainforest floor and nocturnal species. Open woodland and canopy species should be given 5-12% and desert species should be provided with as high as possible including mercury vapour bulbs where possible (discussed below).
Different lighting options:
Compact UV bulbs:
The author does not recommend using this type of bulb. They are falling in popularity with the rising popularity of UV tube bulbs and MVBs. They require a fitting similar to a heat bulb/ceramic and so can’t generally be placed over the basking spot (where UV should be highest) and due to their shape and size only give out sufficient levels of UV over a small area. A gravid female agamid owned by the author failed to test dig under a compact UV bulb. It was replaced with a 24” fluorescent tube of the same UV percentages and within a few days the female had constructed her hole. For this reason I personally no longer use compact bulbs. They could possibly work in smaller vivariums but even then, tubes are now made to fit most vivarium sizes.
Fluorescent tube lights:
These have become the standard for providing UV to captive reptiles. Positioned correctly across the entire length of a vivarium and of the right percentages they can provide all of the UV a reptile needs. For arboreal species that can get closer to the bulb they can be attached to the vivarium roof but in terrestrial species older bulbs should be lowered (not as much of an issue with the latest models which can provide UV over a greater distance than older models).
Mercury vapour bulbs (MVB):
These provide heat and UV in one screw fitting bulb. They provide by far the greatest outputs of any options mentioned here and, positioned correctly can account for the heating of a vivarium as well. They do however have many disadvantages including their expensive prices per bulb (but are cheaper than buying a heat source, a thermostat, a UV light and a starter unit), their generally large sizes and the fact that some inferior makes and older models may lose up to 30% of their UV output in the first month of use. MVBs are recommended for such genera as Uromastyx, Leiolepis, Sauromalus and any lizards that inhabit extremely hot deserts but not for rainforest floor species, nocturnal species or species requiring high humidity due to the intense heat from the bulb. Care must be taken that the vivarium is large enough and a great enough clearance is achieved between the heated surface and the bulb as at point blank range these bulbs can get extremely hot and cause overexposure to UV. A friend of the author’s obtained a European MVB used in tanning salons of 300W that emits massive amounts of UV radiation. This keeper removes each reptile from its vivarium once a week and exposes them to this bulb for 5-10 minutes (bearing in mind that in the wild they are all inhabitants of very hot areas). This has proved sufficient to keep some species without UV bulbs in their vivariums and has led to breeding success with some seldom seen species.
Whichever type of bulb is ultimately used the keeper must make note of when it is first used and aim to replace it by the date the manufacturer advises.
Unfiltered sunlight is undoubtedly beneficial to reptiles but due to the UK’s generally unfavourable climate for reptiles most tropical species cannot be kept outdoors. Having said this, the author has personally discovered Viviparous lizards Zootoca vivipara basking on days where the surface temperature was well over 40C. On sunny days reptiles can be transferred into temporary mesh vivariums where they will often display brighter colours than when kept indoors. A way around this is to keep certain hardy reptile species (notably the members of Laudakia which can survive massive temperature gradients) outdoors under cover of a greenhouse built of glass that doesn’t filter UV radiation which has proved very successful for many experienced herpetoculturists.
Treatment of metabolic bone disease
Metabolic bone disease can only be fully reversed when detected early on. The use of certain brands of MVBs in the U.S.A has cured Green iguanas suffering from MBD. If MBD is suspected reptiles should be immediately taken to a specialist exotics vet who will be able to advise on what action should be taken. Husbandry issues should be immediately addressed to avoid worsening the condition: the UV bulb should be replaced (or included if there wasn’t already) and the diet should be heavily supplemented. In advanced cases especially where the disease prevents the reptile from feeding different forms of calcium must be injected directly. Appetite may return and trembling and partial paralysis may be cured by treatment but damage to the spine, bones and any resulting internal injuries will probably remain.
At first glance it may appear that all of the popular lizard species namely Leopard gecko Eublepharis macularius, Green iguana Iguana iguana, Bearded dragon Pogona vitticeps, Veiled chameleon Chamaeleo calyptratus, Crested gecko Rhacodactylus cilliatus and Green water dragon Physignathus cocincinus are all very susceptible to metabolic bone disease. This is due to the fact that not only are these species the most common in the hobby but they are viewed as “easy” species to keep and are readily available in pet shops to be bought by keepers that won’t have done their research thoroughly enough or are inexperienced. Many are then kept in suboptimal conditions leading to misleadingly large numbers of MBD cases. Truly susceptible specimens are fast growing youngsters who require large quantities of calcium for bone growth notably young water dragons Physignathus and Sailfin dragons Hydrosaurus. Another group that are particularly at risk are gravid female oviparous species where, if sufficient calcium is not made available in the diet to form the egg shells, it will be drawn from the female’s bones. The eggs may be laid with distinctive pink patches on them- a sign of calcium depravation. As MBD is caused by keeper ignorance it would be fair to assume that the species requiring the most exacting conditions to thrive i.e. the species rarely seen in the hobby will be most susceptible to the condition, not through any inherent biological trait but through the lack of knowledge and previous experience with them and conversely, the most commonly kept species should rarely develop the condition with care guidelines provided by people that have kept the species for years.
Chameleons, like many lizards are particularly susceptible to metabolic bone disease; notice the extremely large and debilitating link in the spine of this specimen. Image kindly supplied by Saedcantas
Metabolic Bone Disease (MBD) Summary
As keepers of reptiles we have full responsibility over their lives and health. We owe it to these animals to provide the best possible care and continually research any new breakthroughs in the field. We should always strive for the most suitable equipment for vivariums, no matter the cost and be prepared for any situation. As with most conditions affecting reptiles metabolic bone disease is very easily prevented in most cases but it is much harder to reverse its effects once it has taken hold. Prevention is by far the best cure: research dietary requirements not by posting publicly on internet forums but by asking certain experienced keepers that can prove their experience with specific species or genera (and not ones that have kept an unrelated species alive for a few weeks). The right forums are a goldmine of knowledge when used correctly but use with caution and obtain evidence from a few reputable sources before following advice. Books are useful but where possible avoid very early material and check review websites. Scientific literature, where available, can give exact diets of wild specimens and some papers are written on the captive care of some species.
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