Metabolic Bone Disease, also referred to as “MBD,” is defined as a bone disorder, causing soft, brittle, weak and/or porous bones, and irregular shell growth in tortoises and turtles. While irregular growth on the shell is the most obvious, many more problems lie under the surface, because all bones are affected.
MBD is a common problem in captive tortoises, especially in those who are young and still growing. It is caused by a combination of issues: Insufficient natural sunlight (and therefore, inadequate intake of Vitamin D,) and an insufficient diet. Diets high in phosphorus and low in calcium and other trace elements, and improper temperatures in the captive environment are all contributing factors.
One of the most common visible signs is called “pyramiding,” which refers to an uneven “stacking” of the scutes (the bony keratin sections, and bone layer beneath) rather than smooth growth resembling the Egyptian and Aztec pyramids.
This tortoise has been provided with adequate, full-spectrum sunlight, a diet high in calcium, low in phosphorus, oxalates, and plant proteins.
It’s diet consists entirely of weeds, grasses, wildflowers, and occasional treats such as mulberry leaves and rose petals.
A small but very shallow water pond (which can be made by sinking a large plant saucer level with the ground) is provided for drinking and soaking.
Sadly, the result of inadequate diet and care can have devastating consequences. Deprived of natural sunlight, the proper vitamins, minerals, trace elements, and fed an unhealthy diet containing harmful items her entire life, this tortoise was eventually turned into a sanctuary.
This Sulcata will always require specialized care.
Unable to extend her neck and head over her severely deformed plastron, she is unable to graze, or to pick up food items by herself. She will require hand feeding for the rest of her life.
Pyramiding and Metabolic Bone Disease doesn’t stop with what we see on the “outside.” This Desert Tortoise, like so many others, has significant health issues due to improper husbandry. What cannot be seen are porous, weak bones, and permanently damaged renal systems. Tortoises like these are often carrying one or more large bladder stones, and have damage to their bladder walls, as well as their kidneys, which can be very painful, and can eventually cause death.
This graph is of the density (hardness) of the shells of California desert tortoises as measured in the wild. As you can see, a high calcium, low phosphorus diet, as well as full-spectrum sunlight, is absolutely critical for normal shell development.
For further information about food items that are often fed to reptiles: Analysis of Unhealthy Food Items Fed to Tortoises