What is Metabolic Bone Disease (MBD)
John, a red-bellied cooter with MBD, has an advanced case of MBD.
Reptiles require sunlight to truly flourish. Most reptile species do not absorb Vitamin D very well, so exposure to ultraviolet light is needed for reptiles to manufacture their own Vitamin D. This is something very important to keep in mind because Vitamin D (especially D3, the active form of Vitamin D) is vital to calcium metabolism. A lack of Vitamin D can result in metabolic bone disease (MBD), also known as secondary nutritional hyperparathyroidism or osteoporosis. While MBD is not a calcium deficiency, the main cause of the disease is the inability to correctly metabolize calcium (an improper calcium/phosphorous ratio can also be a primary cause of the disease).
Metabolic bone disease can result in some very severe symptoms. When calcium levels are very low, the reptile’s body will try to compensate by cannibalizing it’s own resources – in this case, the bones. With such low calcium levels, the bones become soft and susceptible to damage. With turtles, this also extends to the shell and can lead to deformities that may later cripple the turtle. A turtle’s unique physiology (the fact that it’s ribs and spine are fused to the shell) means that as the shell deforms, it is in the perfect position to pinch, restrict or otherwise damage the spine.
In addition, calcium plays an important part in muscle contraction. Muscle contraction is regulated by the level of calcium ions in the cytoplasm.
Upon entering the cytoplasm, the calcium ions binds to troponin causing it to change shape. This moves the tropomyosin off of the actin-myosin binding sites. From there ATP binds to a portion of the myosin (the “heads”) and causes it to change conformation, resulting in a contraction. Basically, the calcium is what allows the two muscle filaments to bind together. Add in some energy in the form of ATP and now the muscles can contract. However, this means that without calcium, muscles cannot contract… including the heart.
This is only the start of the health problems MBD can cause.
Ringo, at his June 3rd intake exam.
Unfortunately, this disease is not rare, especially in cases of improper husbandry where the animals are not provided with proper lighting. Recently, during the red bellied-cooter round up, five turtles came to our facility with a fairly advanced case of MBD. They are currently undergoing treatment, but it is highly unlikely that they will all recover enough to be releasable. Unfortunately, Ringo, who had the most advanced case of the disease did not survive. This article is in memorial to him.
Sources:
Acierno, M., Mitchell, M., Roundtree, M., and Zachariah, T. Effects of ultraviolet radiation on 25-hydroxyvitamin D3 synthesis in red-eared slider turtles (Trachemys scripta elegans). AJVR, Vol 67, No. 12, December 2006.
Bluvias, Jessie E. and Karen L. Eckert. 2010. Marine Turtle Trauma Response Pro-cedures: A Husbandry Manual. Wider Caribbean Sea Turtle Conservation Network (WIDECAST) Technical Report No. 10. Ballwin, Missouri. 100 pp.
Jacobson, E.R., What is a healthy reptile? Washington State University 2011. http://campusvet.wsu.edu/infofac/healthyreptiles.htm
Common Turtle Illnesses website.
http://www.personal.psu.edu/pjg5127/IST250/illnesses.htm#MBD
Posted by Dimitria G.
Dimitria is a Summer, 2013 Intern at the National Marine Life Center. She is a sophomore at U Mass Dartmouth majoring in Biology.
This is a great explanation of metabolic bone disease. Thank you, Dimitria! I learned a lot from your post.
Thank you for this excellent article, Dimitria! It gave me a better understanding of MBD.
[…] Turtles share the same mechanism. If they manage to live with a broken—or painted—shell, the vitamin D levels will drastically drop. In turn, the calcium in their bones and shell will be slowly depleted. This is, in fact, a pretty common disease known as a metabolic bone disease (MBD) […]
[…] Our skin absorbs UV light which triggers the production of vitamin D and thishelps in the breakdown of the calcium in our bodies. The same mechanism applies in turtles. If your turtle can live with a broken or painted shell, the vitamin D in its body will drop drastically and this will, in turn, affect the calcium levels that will slowly get depleted causing metabolic bone disease. […]
[…] their shells and bones will not grow properly. Without enough UVB light, turtles will suffer from metabolic bone diseases that are painful and […]
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[…] we just said above, metabolic bone disease (MBD), also known as soft shell syndrome, and shell rot are the two main culprits behind shell softening […]
[…] Metabolic Bone Disease (MBD) is a common ailment affecting turtles, including reptiles. It’s a condition that primarily results from improper nutrition and affects the bones and shells of these animals. […]
[…] levels of oxalates. Oxalates can bind to calcium, preventing absorption and potentially leading to metabolic bone disease (MBD), a severe condition affecting a turtle’s bone […]