Poor diet can lead to malnutrition and nutrient deficiencies.
This text provides information on Metabolic Bone Disease and its symptoms and causes; on the important components of nutrition and their significance; on calcium homeostasis; on disruption of calcium homeostasis due to malnutrition; and lastly, dietary recommendations for avoiding deficiency syndromes.
The name “Metabolic Bone Disease” (MBD) is a collective term for several disorders arising from an imbalance in the proportion of calcium, phosphor, and vitamin D3 in a diet, or in conjunction with the ingestion of other substances that disrupt the ingestion, absorption, secretion, or utilization of calcium, phosphor, and vitamin D3 (e. g., fat-soluble vitamins, minerals). Demarcation from other metabolic diseases is not very simple and is also defined differently in currently available literature. Essentially, the effects can be described so that either too little calcium can be ingested and utilized or that calcium is even leached from the bones to be made available for other processes.
MBD in the clawed frog X. laevis was described as early as 1950; additional cases have since been proven and documented in various types of frogs (R. catesbeiana, P. adspersus, C. ornata, L. pentadactylus, L. infrafrenata, H. andersoni), in toads, in the Axolotl (A. mexicanum), and in Caecilians (D. mexicanus). [1]
The symptoms of MBD are varied and not always easily discernible from other disorders for the layman. Signs of a possible affliction include [1], [5]:
- Deformation of the lower jaw (open mouth, “laughing” Axolotl)
- Abnormal posture with splayed extremities
- Curvature of the spine
- Physical inactivity
- Bone fractures
- Muscle cramps, spasms, trembling
- Edema, bloated body
- Prolapse of intestine and/or cloaca
The following two photos show an axolotl with a deformation of the lower jaw, probably caused by malnutrition in early years. In the left photo, the animal is showed alone; the right photo shows it in comparison with a well nourished and developed animal.
Positive identification is only possible using X-ray, which usually detects decreased bone density. A visit at the veterinary is therefore unavoidable in such cases.
The next photo shows an X-ray of a normally developed and mineralized axolotl skeleton. The sharp contrast between the bones and the surrounding tissue shows the exemplary nourishment of the animal.
With axolotls and other aquatic amphibians, some of the symptoms described above appear very late because, for example, broken or misshapen bones are avoided or unlikely because buoyancy prevents the animals from carrying their total body weight.
MBD is caused by inappropriate or inadequate nutrition. This not only includes feeder animals or foodstuffs that contain too little of specific components; it may also occur when the most important components are present in excess or in the wrong proportion.
To explain this balance, we will first describe the relevant components and their significance for metabolism before listing problems that can arise with specific foods.
Components of Nutrition and their Significance
The following components of nutrition are significant in connection with MBD:
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Calcium: Calcium (Ca) is an essential mineral that is normally found in the body bound up to 99% to the skeleton. The remaining 1% is in other body tissues and fluids. In the skeleton, calcium serves a supporting function; among other things, it is also important for muscle contractions, vision, and cell division. Freely available calcium is absolutely necessary for these processes, and its concentration is held largely constant through metabolic processes. [8]
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Phosphor: Together with calcium, phosphor (Po) is an important component of the skeletal structure and, among other things, plays a part in regulating the acid-base balance and energy metabolism. [Link]
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Vitamin D*: The most important form of vitamin D is vitamin D3. In most animals, it can be produced in the body with help from UVB rays. Because amphibians are generally only exposed to little or no UV light, though, they must acquire vitamin D3 directly from their food. D3 serves various functions in the body. It maintains the level of calcium and phosphate in the blood, thereby (indirectly) providing for the mineralization and demineralization of bones. It regulates calcium and phosphate absorption in the small intestine, and it plays a part in several cell differentiation processes. Vitamin D is fat-soluble and can accumulate in the body when in surplus.
- Vitamin A: Vitamin A has important functions for vision as well as for cell growth and cell differentiation. In amphibians, it is essential for regeneration. Vitamin A also belongs to the fat-soluble vitamins and when in surplus can accumulate in the body (especially in the liver).
Calcium Homeostasis and Interactions of the Individual Components
With feeding (and nutrition in general) the maxim “more is more” does not apply – neither to the amount of food nor to the amount of vitamins and minerals. It is much more important to heed the interrelations and interactions of the individual components.
With ideal nutrition, calcium homeostasis proceeds as follows:
- Calcium and phosphor are ingested in food.
- Ca and Po are absorbed in the small intestine with help from active vitamin D3.
- These minerals are provided to the body via the bloodstream for normal muscle and nerve functions and stored in the bones.
- Excess calcium is excreted via the digestive tract.
This process is disrupted if the essential calcium level in the blood is too low. This calcium level is maintained by several hormones. If the calcium level falls below a certain value, calcium bound in the skeleton is leached to return it to a normal level. This ensures the normal function of nerves and muscles; at the same time, though, the calcium content of the bones is reduced. If these reserves are depleted, movement disorders will occur. [4]
A disruption in the blood calcium level occurs when either too little calcium is available in a diet or when calcium cannot be adequately absorbed in the small intestine for the following reasons:
Excessive phosphor in the diet / false Ca:Po ratio
If a diet includes an adequate amount of calcium, its absorption in adequate amounts can be disrupted if the level of phosphor in the diet is too high. The recommended values for an adequate calcium:phosphor ratio varies slightly between 1:1 to 2:1 [2], [4] and 1.5:1 to 2:1 [5]. In any case, the diet should include at least as much calcium as phosphor on a middle-term average. This is difficult for amphibians in connection with many types of foodstuffs and feeder animals that contain an excess of phosphor (see also nutritional values).
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Vitamin D3 Deficiency in Nutrition
Because amphibians can produce only limited or no vitamin D3 themselves, it must be ingested directly with their food. For this reason, it is important to note when using dietary supplements (mineral powders, vitamin powders) that the supplement does not contain (cheaper) vitamin D, but exclusively contains D3. If a diet's level of vitamin D3 is too low, the small intestine cannot absorb an adequate amount of calcium, even if the calcium is available in theoretically sufficient amounts.
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Vitamin A Excess in Nutrition / Hypervitaminosis A
It has been proven that an excess of vitamin A in a diet prevents vitamin D from maintaining the normal level of calcium in the blood and that there is a biochemical interaction between vitamins A and D and the calcium regulating hormones. [7], [6]. The first documentation of MBD in clawed frogs was also proven in connection with an excess of vitamin A. [1]
Recommendations for the Vitamin A : Vitamin D3 ratio sometimes vary greatly and range from 10:1 [2], so ten times the amount of vitamin A as the amount of vitamin D3, to 1:1 for geckos. [9] Supplements specifically developed for amphibians, such as Herpetal Amphib, follow this specification.
To prevent metabolic bone disease, the amphibian keeper should carefully consider the nourishment of his animals. In summary, the following recommendations can currently be made:
- In general, a diet should be as varied as possible and closely imitate the animal's natural food spectrum. This includes a major share of fresh, live foods.
- Foodstuffs should on average contain an adequately amount of calcium. For example, fish are best fed as whole fish (with bones, alive or dead).
- The Ca:Po ration should be at least 1:1. 2:1 or higher is generally better.
- The ratio of vitamin A to vitamin D3 should be no more than 10:1. This ratio can be adjusted in feeder animals with appropriate diet (foods with less vitamin A). Artificial foodstuffs should be selected according to the list of ingredients.
- It is recommended to improve the value of feeder animals before feeding them to amphibians, either by dusting or by so-called “gut loading” (feeding with appropriate nutrients).
- Any additional ingredients or supplements must contain vitamin D3, not vitamin D. Here, too, the vitamin ratio must be noted!
*About vitamin D: Technically, this is not a vitamin, because the body can synthesize it.
Sources:
- Wright, Kevin M., Whitaker, Brent R.. Amphibian Medicine and Captive Husbandry. Krieger Publishing Company, Malabar, 2001.
- Kowalski, Ed; Philadelphia Zoo, Dept. of Herpetology. Metabolic Bone Disease from the Herpetoculturist's Perspective. Online-publication.
- Kowalski, Ed; Philadelphia Zoo, Dept. of Herpetology. Nutrition for Amphibians and Reptiles in Captivity. Unpublished; personal communication
- Delport, Renier. Metabolic Bone Disease (MBD) In Reptiles & Amphibians. Online-publication 2005.
- Wissman, Margaret A. Metabolic Bone Disease. Online-publication 2006.
- Penniston, Kristina L., Tanumihardjo, Sherry A.. The acute and toxic effects of Vitamin A1-4. The American Journal of Clinical Nutrition 2006.
- Forsmo, S. et. al. Childhood Cod Liver Oil Consumption and Bone Mineral Density in a Population-based Cohort of Peri- and Postmenopausal Women. The Nord-Troendelag Health Study. American Journal of Epidemiology, Vol. 167, No. 4 2007.
- Deutsche Gesellschaft für Nährstoffmedizin und Prävention (DGNP) e. V., Vitalstoff-Lexikon
- Bartlett, Richard D. Geckos - A Complete Owners Manual. Barron's Educational Series, 1995
© Ambystoma.de 2010
Translation by Eva "blueberlin" Kretschmar
