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Metabolic Bone Disease, commonly referred to as MBD, is a general term that is applied to a host of health problems commonly seen in captive reptiles and amphibians. Basically, the condition arises from a lack of dietary or skin-generated Vitamin D3, low calcium levels or an imbalance in the calcium/phosphorous ratio (or a combination of these).
Normal Calcium Metabolism in Herps
Reptiles and amphibians need Vitamin D3 in order to effectively utilize the calcium that is contained in the foods they consume. Calcium plays a vital role in a number of metabolic processes, including bone growth and repair and muscle contraction. Proper functioning of the overall process also depends on the maintenance of the correct ratio of calcium to phosphorous. This ratio is believed to be 2:1 for most reptile and amphibian species, but we have a great deal to learn in this area.
Reptiles That Bask
Heliothermic reptiles (those that bask in the sun) cannot, as a general rule, utilize dietary Vitamin D3 (please see my article, Has Anyone Seen This – Madagascar and Standing’s Day Geckos Maintain Excellent Health and Reproduce Without a UVB Source for a discussion of exceptions). Instead, they rely upon Vitamin D3 that is produced in their skin by the action of UVB light upon skin cholesterols.
In order for Vitamin D3 synthesis to take place, heliothermic reptiles must be exposed to UVB light rays in the range of 290-310 nanometers. Window glass filters out beneficial UVB rays - unless your reptiles are exposed to unfiltered sunlight on a regular bass, they must be provided with a high quality UVB bulb placed at an appropriate distance (see manufacturer’s recommendations) from the basking site.
Reptiles in this category include semi-aquatic basking turtles (Red-eared Sliders, Painted Turtles), tortoises and terrestrial turtles (Greek Tortoises, Box Turtles), diurnal lizards (Green Iguanas, Bearded Dragons) and all crocodilians (NOT recommended as pets).
Nocturnal and Non-Basking Herps
These creatures utilize dietary Vitamin D3. As long as the calcium/phosphorous ratio is appropriate (please see below) and adequate amounts of Vitamin D3 and calcium are provided, they will get along well without a source of UVB light. In fact, many amphibians have UVB blockers in their skin, and may suffer health problems if over-exposed to UVB in captivity.
Animals in this category include Musk and Snapping Turtles, Leopard and Tokay Geckos and most if not all snakes and amphibians.
There is some anecdotal evidence that a few snake species (Keeled and Smooth Green Snakes, North American Garter and Water Snakes) may fare better in captivity when kept under UVB light. I’ll keep you posted as further information becomes available.
Symptoms of Metabolic Bone Disease
Animals suffering from a calcium deficiency brought on by inappropriately low levels of calcium/Vitamin D3, or a skewed calcium/phosphorous ratio, often leach calcium from their bones and put it to other uses. As a result, the bones become thin and fragile, and are easily broken. In advanced cases, the limbs will not be able to support the animal as it tries to walk or climb and it will consequently move little and rest in an unnatural position.
As the bones weaken, muscle pressure against them (or perhaps muscle growth) may cause malformations, resulting in lumps and crooked limbs, jaws and backbones. The body sometimes lays down fibrous tissue to replace the bone mass that has been lost to calcium leaching, resulting in swellings and soft bumps. In turtles, the plastron and/or carapace may become soft or pliable. Muscle tremors (tetany), constipation and anorexia set in as the condition progresses.
Treating Metabolic Bone Disease
A veterinarian should be consulted if MBD is suspected. Over-the-counter NeoCalglucon, administered orally, may be recommended in the disease’s early stages. Advanced cases will require more aggressive treatment, including injections of calcium gluconate. Depending upon the species, you may also need to increase your ambient and basking temperatures and provide increased exposure to UVB light.
Species and Individual Animal
Specifics concerning the foregoing information will vary widely from species to species, and within each species depending upon the animal’s age, general health and reproductive condition. Please write in with questions concerning those reptiles and amphibians which you keep. Ultraviolet A Light
Ultraviolet A radiation is important in maintaining normal behavior in most reptiles and amphibians, even those that do not bask. As this will ultimately affect appetite, calcium metabolism and general health, your pets should always be provided with a UVA source. Environmental Conditions
No matter how a species obtains Vitamin D3 and metabolizes calcium, the process will not function properly if the animal is stressed by inappropriate environmental conditions – heat, humidity, day/night cycle, cage-mates and terrarium set-up and location must all be in order. Inattention to these details will also impact your pet’s immune system, leaving it prone to a wide range of health problems. Dietary Quality and Variety
All reptiles and amphibians, whether or not they bask, must be provided with adequate amounts of calcium in proper proportion to phosphorous, and with dietary Vitamin D3. Feeder insects should themselves be fed a nutritious diet (please see my article, Providing a Balanced Diet to Reptile and Amphibian Pets) so as to pass on valuable nutrients to the animals that consume them, and a wide variety of foods utilized. Canned insects and light traps are very useful to those maintaining insectivorous species. Vitamin Mineral Supplementation
Dusting your pet’s food with a vitamin/mineral supplement is another method of adding calcium and Vitamin D3 to the diet. However, this cannot be done indiscriminately, as too much can be as bad as too little.
We know very little about the exact needs of many species, and that which we do know is tempered by many factors. Overall composition of the diet is extremely important in determining the proper dosage of vitamins and minerals. For example, a Mexican Axolotl being fed a diet comprised of Reptomin Food Sticks, earthworms, blackworms, minnows and canned shrimp will require no supplementation, while a hatchling Leopard Gecko subsisting on crickets and waxworms will likely require additional vitamins and minerals with most of its meals. Please write in with questions concerning specific pets and situations. Thank you.
A technical article dealing with calcium deficiencies and other non-infectious diseases in reptiles is posted at: