Current thoughts on reptile nutrition (Proceedings)
General considerations in reptile & amphibian nutrition
In general, information about an animal's origin and natural history is often the basis for recommendations concerning dietary management of these animals in captivity. In captivity, whether in an aquarium, screened cage, or (inappropriately) loose in the house – reptiles and amphibians have specific ranges for temperature, humidity, and ventilation which are essential for optimal health. Maintenance of an animal outside of its optimal range is a physiological stress that often results in poor intake, digestion/absorption, and utilization of food. Animals not properly maintained will fail to thrive and often die. Also, reptiles and amphibians have specific requirements for habitat size, substrate, cage accessories, lighting, and social interaction. The failure to provide them with their environmental needs, and with suitable gradients that allow choices within this space, can lead to stress, with negative effects on food intake and metabolism. Thus, poor husbandry can have a significantly negative effect on an animal's nutritinal status, so that even a superior diet that is "complete and balanced" will fail to meet the nutritional needs of the animal.
The field of veterinary nutrition is a continually evolving science, and this could not be truer for reptile and amphibian nutrition. The science of reptile nutrition is growing every year, but is still hampered by trying to determine normal baseline diets for many species. With over 10,000+ species of reptiles and amphibians, there is relatively little data on what most of these animals actually eat, not to mention the nutritional composition of these diets. With this being said there still are a number of basic nutritional guidelines for which to follow with reptiles and amphibians. In addition to the basics there are a number of new products and ideas which are discussed incontext of their nutritional appropriateness for reptiles and amphibians.Specific numbers are not available, but many reptiles and amphibians die prematurely; malnutrition is often a factor in this early demise. Therefore, a thorough dietary history should be obtained each time a reptile (and/or amphibian) presents as a patient; current and complete diet histories greatly aid the diagnosis of nutritional disorders. Because the exact nutritional requirements and dietary standards have not been established for most reptiles or amphibians, the adequacy of commercial pre-formed and homemade diets should always be questioned. A diet history permits assessment of the animal's intake of energy (calories) and nutrients, and provides information relevant to the animal's clinical condition and attitude. A diet history also helps to detect nutritional problems before they become serious clinical disorders. For many diet-related diseases, nutritional mismanagement has occurred for a long time before clinical signs appear - using diet history as a part of the medical work up strengthens a preventative health program.
For example, the green iguana, Iguana iguana, the second most traded vertebrate species in the world - inhabits the tropical regions of Central and South America. These lizards are known to be arboreal and diurnal. Green iguanas are herbivorous, in the wild consuming a primarily folivorous diet of leaves, blossoms, and fruit. Green iguanas, as is the case with other herbivorous reptiles, have enlarged ceca that make them well adapted for hindgut fermentation. It has been determined that free-ranging green iguanas tend to select plants that contain not only high protein but also relatively high fiber, though very high fiber diets have been found to suppress growth in juvenile green iguanas. It appears that a green iguana diet of greater then 13% crude fiber is desirable. Producers of commercial green iguana diets should provide proximate analysis of their product, which details the contents of essential nutrients and fiber. Products ideally should have been tested in the laboratory and in the animals via feeding trials. Dog and cat foods may contain a label claim of "Complete and Balanced" because there are specific independent standards for nutritional adequacy of these diets. In contrast, commercially produced diets for green iguanas cannot justifiably make such claims because there is no body of scientific data upon which an independent authority could establish a standard for nutritional adequacy.
There are a plethora of nutritional supplements available, with each offering a wide variety in nutrient quantity and quality. Most clients are surprised to discover that they are not providing a completely balanced diet for their captive reptiles and amphibians; supplements are often recommended. However it is often difficult to make specific recommendations because there may be significant differences in quality control of ingredients, manufacturing, and storage of nutritional supplements for reptiles, though these differences are difficult to document.
Calcium deficiency in green iguanas can also arise because of a number of different dietary reasons i.e. - consumption of unsupplemented salads or insufficient legumes. Also calcium absorption may be impaired by diets containing phytates (soy ingredients), oxalates (spinach etc...), high fat (performance pet foods), or acid (certain commercial cat foods) and by diets deficient in vitamin D. Vitamin D3 supplementation is problematic. Limited research data, anecdotal evidence and clinical impressions suggest that dermal synthesis of 1,25-dihydroxycholecalciferol may be more efficient than gastrointestinal absorption of dietary vitamin D3. This impression promotes the use of "full spectrum" lighting - which appears adequate for vitamin D3 synthesis in some species but perhaps not in others. The already confused picture is only further complicated by the interactions between vitamin D, calcium, phosphorous, and secondary interactions with vitamin A and several trace minerals.