Metabolic bone disease (MDB) is a condition that occurs when there is an imbalance between the vitamins, minerals and nutrients that make up bones.
Typically, this is abnormal levels of calcium, phosphorous, vitamin D and UV. This imbalance can lead to soft and weakened bones, deformities, and other health issues. In tortoises, MDB also affects their shell.
Signs and Symptoms
The key physical and behavioral signs that may indicate MBD in tortoises include:
- Soft, misshapen or unhealthy shell
- Lameness, limping or difficulty moving
- Swelling of limbs or joints
- Loss of appetite
- Weight loss
- Weakness and lethargy
- Muscle twitches or rigidity
- Cloacal prolapse
- Inability to urinate or defecate
- Seizures
Diagnosing MBD
Veterinarians diagnose tortoises for MBD based on the symptoms, a physical examination and husbandry evaluation.
To confirm the diagnosis and monitor treatment, further tests may be carried out. This can include radiographs or X-rays to evaluate bone health. As MBD progresses, bones become weak and demineralized due to lack of calcium. Bloods can be taken and tested for low ionized calcium, high phosphorous and low vitamin D3.
Causes
MBD in tortoises primarily results from a combination of dietary and environmental factors.
Nutritional Deficiencies
To grow and maintain strong bones, and to avoid an unhealthy shell and general ill health, tortoises require a diet with the correct proportions of vitamins and minerals. Specifically, they require a calcium to phosphorous ratio of 2:1.
Calcium supports several vital processes, including maintaining bone health. If a tortoise is deficient in calcium, the body will take calcium from the bones and shell in an effort to keep functioning.
This results in a softening and weakening of the bones and shell. This form of MBD is known as nutritional secondary hyperparathyroidism.
Gravid female tortoises (those carrying eggs) require more calcium than other adult tortoises, as it’s needed to form the eggshells. Insufficient calcium will result in improper egg formation and shell collapse.
Phosphorous is important for the formation of bones. However, too much phosphorous will inhibit your tortoise’s ability to absorb calcium, causing weak bones and a soft shell. Therefore, it’s crucial your tortoise’s diet contains the correct 2:1 calcium to phosphorous ratio.
Inadequate UVB Lighting
Vitamin D is required for calcium absorption. Tortoises gain vitamin D through sunlight exposure. In captivity or when kept indoors, this is replicated through ultraviolet (UVB) lighting.
When tortoises don’t receive enough UVB light, they cannot synthesise vitamin D. Low vitamin D levels inhibits the absorption of calcium, leading to a soft shell and bones.
Treating Metabolic Bone Disease
Treating MBD in tortoises involves identifying the underlying causes. Depending on the severity, it can be either treated at home but may also require veterinary care.
Care at Home
If you have caught MBD in its early stages, you may be able to nurse them back to health at home. Evaluate their diet and habitat and figure out what you need to change. Consulting a vet is a good idea so you can discuss what changes need to be made.
Check your tortoise’s lighting. Is the UVB light at a high enough percentage? Does it have a wide enough coverage in the enclosure? You may need to replace or reposition the UVB light to make sure your tortoise is able to synthesize enough vitamin D.
Check your tortoise’s diet. Are they receiving a diet with the correct calcium to phosphorous ratio? You may need to incorporate more calcium-rich foods, such as dark, leafy greens and edible flowers. A vet may even recommend calcium supplements. Additionally, you may need to reduce foods that are high in phosphate.
Veterinary Care Treatment Options
If your tortoise is displaying more severe MBD symptoms, they will likely need veterinary care treatment. Depending on the cause, a vet may prescribe oral or injectable calcium, vitamin D or phosphate binders. Your tortoise may also need fluid therapy or splinting of fractured bones. A vet could also recommend UV light therapy.
Preventing Metabolic Bone Disease
Now you have familiarized yourself with the causes of MBD, you can easily learn how to prevent it from happening to your tortoise. This is achieved mainly through proper husbandry.
Diet
Ensure you are feeding your tortoise a diet rich in calcium. Suitable foods that are high in calcium include dark, leafy green vegetables such as kale and edible flowers or weeds such as dandelions. Be careful not to give them too much calcium as this can lead to hypercalcemia. Additionally, make sure not to feed your tortoise too much phosphorous.
You can also purchase special tortoise food that contains the correct ratio of all the vitamins and minerals your tortoise needs to stay healthy. If you are unsure about what to feed your tortoise, I recommend consulting your local veterinary practice for advice.
Habitat Conditions
Sufficient UV light is required for tortoises to synthesize vitamin D to enable the absorption of calcium. Wild tortoises rely on the sun for ultraviolet light. However, captive tortoises that are housed inside require a UVB light. The light should be kept on between 10 and 12 hours a day to mimic the exposure a wild tortoise would receive.
Furthermore, temperature is another key factor for preventing MBD. Your tortoise’s enclosure should have a temperature gradient. The cool side should be around 72oF to 80oF, whilst the warm side should be between 90oF and 95oF.
Tortoises are cold blooded, so rely on the external environment to control their body temperature. Use heat lamps to provide warmth, and shelter to provide shade.
Without the correct temperatures, your tortoise’s digestive system will be unable to function properly. This means they cannot absorb the nutrients required for bone and shell growth and maintenance.
Monitoring and Regular Check-Ups
Seeking veterinary advice is crucial as MBD can be fatal if left untreated. Regular veterinary check-ups are vital for monitoring your tortoise’s recovery progress and adjusting the treatment plan as required. By receiving the proper care, your tortoise can fully recover and go on to live a full and healthy life.
Citations
- Packerland Veterinary Center – MBD
- California Turtle & Tortoise Club – Calcium:Phosphate
- King British – UVB
