Metabolic Bone Disease & Associated Problems

Appeared in Reptile Care Magazine, Issue 1

As a reptile vet this is probably about the most commonly presented reptile problem.  What is so maddening when compared to some other conditions is that this is completely avoidable.  Metabolic bone disease is a lack of metabolic calcium and is technically referred to as hypocalcaemia.  Problems occur as the body needs calcium for bone growth and muscle contraction.

The consequences of a lack of calcium can vary considerably but are more acute when a reptile is in its natural heavy growth stage.  The requirement for calcium at this stage is at its highest and only manifests in more chronic problems when an animal has passed the early growth stages.

Calcium Metabolism

Problems stem from three principal factors.

1. Calcium Ratios - Most foods used in captivity are either low in calcium or high in phosphate.  An ideal ratio of calcium to phosphate in the diet is 3:1 and thus, as can be seen from figures in Table 1, most foods need some supplementing.  This added calcium balances up the phosphate levels.
2. Vitamin D - Many diets are too low in Vitamin D.  This is needed as when activated by UVB light it gets turned into its active form which is important in the absorption of calcium from the bowel.
3. Ultraviolet Light - The artificial indoor environments we create for our reptiles in the UK suffer from not having access to natural sunlight and certainly not in the same amounts as many diurnal animals from better climates would naturally receive.  Lack of his natural sunlight or good artificial equivalent is probably the single biggest contributory factor to the high incidence of hypocalcaemia problems in the UK lizard and tortoise populations.

Let us look at each of these factors in more detail.

Calcium Ratios

In order to improve the ratio of calcium to phosphate in the natural diet I would suggest that a supplement is added to the diet at every meal.  This takes the form of a calcium carbonate (or calcium lactate) based supplement product, e.g. 'Calypso Dust', 'T-Rex 2:0' or 'Bone Aid Dusting Powder' or in large individuals natural products such as grated cuttlefish or crushed oyster shell.

You can never overdose an animal on either of these products as extra ingested calcium simply passes through the reptile unabsorbed and it is thus best to use it liberally over all foodstuffs.

Vitamin D

There are many products on the market that can be used as a supplement to provide the right amount of Vitamin D.  Available products in the UK include 'Nutrobol', 'Repton' or 'Reptivite' and should be given every 3-4 days only.  These are necessary as they contain many important minerals and vitamins, but in this context it is the vitamin D we are concerned with.

The vitamin D and other fat soluble vitamins in these products are all absorbed from the supplement given and thus this is a controlling factor in the absorption of the ingested calcium.  It is thus possible to overdose on this product so it should be used sparingly.  Having said that my general advice would be to cover the food with a fine dusty layer twice weekly in the growing stages, (or after laying eggs / giving birth) and once weekly on reaching adulthood.

UV Lighting

Ultraviolet light can be divided into three portions depending on its wavelength.

Very short wavelength UV light is termed UVC and this is normally screened out by the ozone layer in the atmosphere.  This wavelength is destructive to our skin, but most artificial bulbs produce no discernible UVC!

Medium length UV light is termed UVB and is the most important to herpetologists in terms of calcium metabolism.  This UVB activates enzymes in the skin which convert the inactive Vitamin D that the reptile has eaten, into the active form.  This active Vitamin D plays a crucial role in the absorption of calcium from the bowel.  Because this is a pathway, all three parts need to be in place ie;

• Sufficient vitamin D in the diet
• Sufficient calcium in the diet
• Sufficient good quality UVB light.

Longer wavelength UVA light is not as directly important to reptiles as the UVB in terms of health, but has a very important role to play in terms of its psychological effects.  This affects their seasonality over time and has a direct effect on their activity levels and eating patterns on a day to day basis.  The effects can be markedly seen in species such as Uromastyx where colouration and activity levels are noticeably changed by increasing levels.  Its importance is often overlooked in other species.

There are four important things to remember when considering UV lighting in reptiles;

1. The lamp to reptile distance - unlike sunlight which travels though the atmosphere to reach us, artificial light dissipated relatively quickly once produced due in part to its divergent source.  It is thus important to have the reptile basking within 12 inches of the light.  This involves lowering the lights so as to enable the reptile to sit closer to it.
2. The concentration of the light emitted - Mercury vapour lamps already have a reflective back which concentrates the light in a cone fashion.  The use of a reflector behind a strip-light will have similar effects in considerably increasing the spectrum that the reptile gets by reducing scatter.
3. The age of the lamp - Active UV bulbs and all strip-lights gradually produce less UV with time.  Most of the lights available will start to noticeably reduce in efficiency after about 1000 hours of use and be of little discernible use by 4000 hours.  Thus although the bulb may continue to emit visible light for a considerable time, this light is often of little use to the reptile.  This means that bulbs will at best last only one year and probably somewhat less.

These are two x-rays of two similar age bearded dragons.  X-ray 1 has low reserves of calcium and x-ray 2 has more normal levels of calcium.  This type of comparison can be better than a blood sample as shows long term levels of reserve calcium.

Concerns

People are often worried about damaging effects of UV light on the skin of their reptiles.  This fear is however groundless in that the UV emitted from even these new lights is only as powerful as UK sunlight.  Not only that, but these animals have evolved to live in climates with very much higher UV levels and will thus show no ill effects from this light being on 12 - 16 hours a day.  Can it harm my eyes if it shines out into a room?  If the light is in a vivarium, ie the light has to penetrate glass, then although this lets through visible light it stops 99% of the UV and thus is scattered light through the vivarium glass is of no concern.

The Disease Consequences

Having established the causes we now have to discuss the consequences for the reptile of a poor regime and perhaps most importantly the treatment of such problems.

Clinical Disease

Signs that your lizard may be suffering from calcium deficiency may be very acute, such as in-appetence, muscle tremors, weakness (seen in Bearded Dragons and other fast growing juveniles of similar species) but some may be more chronic, e.g. slow growth, inactivity, bone swellings, depressed immune system, fractures (especially Iguanas) or spinal deformity.  Too many pet reptiles have shown these sub-clinical signs for a long time and yet owners put it down to the animal being 'the runt' or 'a fussy feeder' etc.

Metabolic Bone Disease in tortoises usually manifests in shell deformity and softness often causing an inability to move.  These initial findings will then progress if left unchecked to a similar collapsed state to that stated for lizards above. And only if that is left.

Treatments

Chronic cases can be treated yourself by the instigation of a good calcium regime as considerable time as in the problem may take many months to materialise in to a clinical problem that is noticed and similarly it may take many months for these signs to regress.  Persevere with good regime and over time most things should slowly improve.  Unfortunately problems with say shell deformity, spinal kinking etc may improve a little, but will always be there causing permanent disfigurement.

In acute cases that are still eating you may be able to turn things around yourself by following the advice below.  In very bad cases where the animal is in-appetent or completely collapsed, it would be best to start with a visit to a reptile vet as these animals benefit from being given an initial injection of calcium, some fluid therapy and possibly antibiotic cover.  If still eating and only weak then start the following regime:

A good calcium regime: This is often best done by starting with a Vetark product called Zolcal-D.  This is a liquid which can be given orally daily at 0.1mls / 100g of reptile and will ensure that the reptile is supplied with a good calcium and vitamin D regime.  This is non-optical in that you have to make sure this is being given no matter how much he reptile fights against you dosing it.  The usual regime is to use this 1-2 weeks until the clinical problems subside and then reduce to giving this dose every 2-3 days and re-establishing a normal power on foods regime.

Good UVB levels:  See the earlier section on UV lighting generally, but basically limit the space available so as the reptile is always maintained close to an appropriate UVB source.  Consider getting a better UV light if you have one of the sub standard types or an old bulb.  This with the Zolcal-D completes the third part of the key components of a good calcium regime.

Fluids:  When the reptile is debilitated it is very important that you maintain good levels of hydration as the reptile would naturally tend to become dehydrated.  This can be as simple as bathing the reptile 2-3 times a day and the soak and drinking can be enough.  In animals weaker and more severely dehydrated there are several reptile products such as Reptoboost that can be used for re-hydration purposes.  These are powers that are reconstituted with water and are far superior to water alone.  As a rough guide most species require about 3-5% of their body weight per day and this equates to 3-5mls to a 100gram reptile.  This is best given in lots of small amounts very frequently; say every hour throughout the waking day.

As stated previously this is a slow process and it often takes up to two weeks to get resolution of the problems faced and return to a normal vitality.  Many reptiles still die of this problem before the problem is fully identified and the above regime can be implemented and take effect.  Please be vigilant and stick to a good feeding and supplementation regime whilst frequently replacing the UV bulb.

By David Feldmar BVMS MRCVS
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