What is Metabolic Bone Disease and Could My Pet Have It?

What pets can get metabolic bone disease?

It is primarily reptiles that have metabolic bone disease when they come to see a veterinarian. The most common species that we see that have metabolic bone disease are bearded dragons and leopard geckos, but any reptile can have the problem.

What is metabolic bone disease?

Metabolic bone disease (MBD) is also called fibrous osteodystrophy, osteomalacia, secondary nutritional hyperparathyroidism, osteoporosis, or rickets. Metabolic bone disease is caused by an imbalance of phosphorous and calcium. It is caused by a lack of calcium, a lack of calcium absorption (more on this later!), or too much phosphorus.

The nitty gritty: the normal blood calcium to phosphorous ratio is 1.5-2: 1, with 2:1 being most ideal. If the ratio drops below this (either from too little calcium or too much phosphorous), the high phosphorous levels will cause the parathyroid gland to secrete a hormone that causes the body to frantically pick up any calcium it can, even from the bone. As calcium is leached from the bone, the body begins to replace calcium with a fibrous connective tissue. This softens the bones and can cause visible lumps in the bones.

Alright, so what causes this ratio to be off and how can I prevent this from happening to my pet?

Generally speaking, MBD is the result of something being off with the pet’s care at home. Most reptiles (with the notable exception of snakes, who ingest bone regularly) require supplemental calcium on their food. Reptiles which are fed insects should have all of their insects dusted with calcium; reptiles fed vegetables should have calcium dusted on their vegetables. This needs to be continued throughout the animal’s life, but it is especially important as they are growing (the first year of life). Many calcium supplements sold for reptiles have vitamin D in them. They do NOT require oral vitamin D, and do not absorb it well. It can even cause problems if given in high quantities. Try to find a calcium supplement without vitamin D so that you cannot overdose. You can give a supplement with vitamin D once weekly, but try to avoid giving it more than that.

Probably the most common cause of MBD in reptiles is a lack of Vitamin D absorbed through light. Vitamin D should be obtained from both UVA and UVB. This is very important in the metabolism and uptake of calcium. UVB bulbs should be provided to all reptiles, but especially the primarily herbivorous species. The bulbs do need to be changed every 6 months, even though it appears they are working, the UVB component generally wears out after 6 months. They need to have this light for at least hours per day, or natural sunlight. This sunlight cannot be filtered by windows, so they would need to spend time outside to replace the UVB bulb. This is generally only possible in the summer months, due to their strict temperature regulations.

Temperature and humidity outside the optimal range can impair digestion, and thus impact their ability to absorb calcium, but this is not as common. Finally, medical conditions unrelated to husbandry, such as kidney and liver disease, can cause impaired absorption of calcium. These are most common in older animals. Rarely, parathyroid gland disease can cause MBD as well, but this is not very common in reptiles.

How do we diagnose MBD? What about treatment?

Your veterinarian will use many tools to diagnose your pet with MBD. Her first step will be a thorough physical examination. She will make sure to watch your pet walk, open your pets mouth, listen to his heart, and feel his abdomen. If warranted, your veterinarian will likely recommend x-rays; this will not only help to confirm the diagnosis of MBD, but will allow pre- and post- treatment comparisons to ensure treatment is complete. You veterinarian may also recommend blood work or other diagnostics to ensure there are no underlying health problems that are causing the issue.

Treatment can be very prolonged, depending on the severity fo the disease. The most important treatment is correction of the environment. Insects can be gut loaded for added nutrients. Temperatures should be adjusted to the ideal for the species. Finally, severe cases will require prescription high-dose calcium from your veterinarian. This may be given orally or injected. Without treatment, pets with MBD are unlikely to get better. If you are worried about MBD in your pet, please contact your veterinarian immediately.