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Low Calcium

One of the most common problems I see with exotics of all kinds is insufficient calcium, or an inability to properly metabolize and utilize calcium. Reptiles and metabolic bone disease are probably the most well known, but this is seen in all kinds of animals. Other common species include frogs and toads, sugar gliders, skunks, raccoons, foxes, primates, and other wild mammals. Hypocalcemia (low calcium) can lead to decreased bone density, muscle tremors, soft/rubbery bones, bone fractures, skeletal deformities, and even seizures. These animals often present for jaw fractures, hind limb weakness/paralysis, bowed legs, and seizures. They may also have a “bump” on their back. On x ray we generally see decreased bone density and bowed limbs. Bones should be bright white, but with MBD they often show up very dull and difficult to distinguish from surrounding structures. So how does this happen?

(Images: A bearded dragon with severe bone deformities and a monitor with rubber jaw caused by an extreme decrease in bone strength and density)

1. Lack of dietary calcium. For reptiles, this usually involves insufficient supplementation. Insects are actually naturally lacking in nutrients; they need to be fed a nutritious diet before being fed to the reptile (gut loading) and dusted with a calcium carbonate based powder. For the mammals, it’s a similar problem but often overlooked. Carnivores and omnivores are often fed skeletal meat (i.e. chicken breast, ground beef) as their primary protein source. Owners mistakenly think this is sufficient calcium, but it is actually lacking. Fruits and dried insects often get overfed as well to omnivores as well. Sugar gliders, for example, often end up on primarily insect and fruit diets that do not meet their needs at all.

(Image: An x ray of a gecko with severe MBD. Notice how there is virtually no distinction between the bone and the soft tissue. You can’t tell that this gecko has a skeleton)

2. Improper supplementation. Phosphorus and calcium work as opposites, so sometimes animals are fed enough calcium, but too much phosphorus. Most animals need a Ca:P ratio around 2:1. Either foods or supplements can be too high in phosphorus.

(Image: A sugar glider with hind limb paralysis secondary to low dietary calcium)

3. Lack of vitamin D. This is mostly reptiles that lack a sufficient UVB source, but could occur in any animal that lacks sufficient vitamin D. Vitamin D is needed for calcium metabolism. Commonly with reptiles, UVB is either skipped or not replaced regularly. UV bulbs can continue to give off light even when the UV is not sufficient. Recommendations are to change every 6 months unless you are measuring output. Vitamin D3 can be supplemented but is not utilized as efficiently as “homemade” D3 from UVB.

4. Other health/husbandry issues. Kidney disease can lead to decreased vitamin D activation, and GI disease can cause decreased calcium absorption in the GI tract. Too much fat also impairs calcium absorption, and reptiles kept at low temperatures have overall decreased metabolism and digestibility. Oxalates (more on that below) also bind calcium and prevent absorption. Overfeeding foods high in oxalates can also disrupt calcium absorption.

What About Too Much Calcium?

It’s not as common, but animals can absolutely be overfed calcium and/or vitamin D. Generally this occurs with over-supplementation of a synthetic calcium + vitamin D source. Rabbits and Guinea pigs are also prone to bladder stones and urinary “sludge” from excess calcium sources or sources that contain high amounts of oxalates (such as spinach). Certain cancers can also cause hypercalcemia (inc calcium), as can parathyroid gland disease.