Nutrition in Reptiles

Also see Management of Reptiles.

Appropriate husbandry of reptiles is as important as providing adequate nutrients See table Composition of Animal Foods that May Be Offered to Reptiles. Photoperiod, temperature, humidity, substrate, stress, and cage “furniture” can affect feeding behavior and, thus, nutrient intake. Temperature and humidity gradients within a reptile enclosure allow the animal to select warm, dry spots or cooler, moist areas. Competition for preferred sites and for food pans in an enclosure with multiple animals should also be assessed. Sufficient numbers of warm spots, UVB exposure spots, and food pans should be available for all animals within an enclosure. Visual barriers may be useful to reduce competition for preferred sites or food dishes.

Prey such as rabbits, rats, or mice should come from commercial breeding centers and be offered dead to prevent injury to the reptile and for welfare reasons of the offered prey. Although it is not common, prey have been known to attack predators and can inflict serious bites. Offering dead prey can also reduce the chance of injury to the predator caused by striking the walls of the enclosure. However, some reptiles may initially need the stimulation of live prey, particularly if they are not adapted to captivity. The possibility of disease or parasite transmission from prey to predator should be considered.

Vertebrate prey should be fed nutritionally complete diets appropriate for the species (eg, mouse diet, rabbit diet, rat diet, etc). The nutrient content of the prey depends on what it is fed (eg, mice raised on a diet deficient in vitamin A have decreased liver storage of this essential nutrient). Additionally, if frozen mice or rats are routinely used to feed carnivorous reptiles, freezer storage conditions should be optimal (eg, ≤6 months and in thick, plastic bags to retard deterioration, stored at -20°C). Methods of thawing that minimize water loss are also important. Because many carnivorous reptiles rely on their prey not only as sources of nutrients but also as sources of water, the state of hydration of the prey can be very important. Thawing should be done in a cooler at < 8°C.

Familiarity with a species’ food habits in the wild is essential if appropriate foods and nutrient levels are to be offered. Common practice has been to offer two or more different prey species, because differences in nutrient content exist among vertebrate and invertebrate prey. Reduced dependence on a single food or prey species is also desirable, because some prey items may be periodically difficult to obtain. Dependence on a single prey item is frequently seen in snakes and may be unavoidable.

Many commercial diets for reptiles are marketed. Products for carnivorous, herbivorous, and omnivorous reptiles are now available in frozen, freeze-dried, canned, extruded, pelleted, or sausage forms. Acceptability may be better when the commercial diets are offered to reptiles when they are young. Appropriately formulated, manufactured diets for reptiles are a potentially simpler and more economical alternative to feeding fresh produce or live prey. However, some of these diets may not be formulated rationally, and frequently little information concerning micronutrient concentrations is provided by the manufacturers. When selecting a commercial product, the buyer should obtain accurate information about product formulation and specific nutrient concentrations. Unfortunately, little controlled research has been conducted on nutrient requirements of reptiles, and claims of product superiority may not have a scientific justification. ( See table Composition of Animal Foods that May Be Offered to Reptiles)

Herbivorous reptile pellets should make up 25%–50% of the diet of herbivorous reptiles. Animals should be fed 1%–4% of their body weight on a dry-matter basis. Vegetables with a low amount of oxalate should be fed to prevent kidney stones. A good quality grass hay or a so-called herbs-hay should be fed. No more than 50% of the diet should consist of fresh greens, fruits, and vegetables. The amount of fruit should be no more than 5%. In Europe, often herbs and dandelions are fed to herbivorous reptiles. Fresh, clean water must be available at all times.

See table Recommended Nutrient Concentrations for Reptiles for recommended nutrient concentrations for reptiles.

Vitamin C synthesis has been reported in many reptile species. It has been suggested that ulcerative stomatitis seen in snakes and lizards may be associated with a vitamin C deficiency, although there is no supportive evidence. In controlled studies with garter snakes (Thamnophis sp) fed supplemental vitamin C, tissue levels and body stores remained stable, although synthesis by the snakes was reduced.

Although most reptiles excrete nitrogen primarily as uric acid, aquatic reptiles typically excrete excess nitrogen as urea or ammonia. The relative proportions of various nitrogenous wastes may depend on the amount and composition of feed, frequency of feeding, and state of hydration. The excessive precipitation of urate crystals in joints, kidneys, or other organs (gout) can be a common condition in some species of captive reptiles. The etiology is not clear, but it is commonly thought that diets high in protein may predispose reptiles to gout. Impaired renal function and dehydration have also been suggested as possible causes.

If poor-quality protein is fed (unbalanced amino acids) or when tissue is catabolized for energy, uric acid excretion increases. Although gout in some reptiles is associated with increased circulating levels, postprandial transient increases in circulating uric acid may be seen in some species and confound the diagnosis. Assuring an adequate state of hydration in a susceptible animal may help prevent uric acid precipitation in joints and organs. Feeding diets low in protein to carnivorous reptiles is unwise, because they are adapted to feeding on high-protein prey.