The field of zoo and exotic animal nutrition has made significant advances in recent decades. Exotic animal nutritionists in zoos and in the feed industry are studying problems and generating information on proper nutritional management for many species.
All animals require nutrients and energy in a metabolizable form. The nutrients and energy must be properly balanced and in the correct form to accommodate particular tastes, digestive systems, and feeding methods. For example, large psittacines typically use their feet for holding food, while other species obtain or position food using other appendages (or they do not manipulate food). If a commercial extruded food is fed, the pieces must be large enough for the bird to grasp easily. Diets for exotic and zoo animals have been developed by considering food habits in the wild, oral and GI tract morphology, nutrient requirements established for domestic and laboratory animals and people, nutritional research on exotic species, and practical experience. The ultimate criteria for evaluating the suitability of a diet for a given species are growth, reproductive success, and longevity.
The minimum nutrient requirements established by the National Research Council (NRC) for domestic and laboratory animals can be useful starting points in setting target nutrient levels for an exotic species. For example, the Nutrient Requirements of Small Ruminants published by the NRC in 2007, contains nutritional information on cervids (white-tailed deer, red deer, wapiti, and caribou) and camelids (llamas and alpacas). In addition, the NRC guidelines for nonhuman primates have been updated.
For many exotic species that have closely related domestic counterparts, diets can be formulated to contain nutrients that would meet the requirements established for ungulates, mustelids, canids, felids, rodents, primates, lagomorphs, gallinaceous and anseriform birds, and fish. However, nutrient requirements established by the NRC should be used only as guidelines, because the goals of livestock producers in feeding their animals include rapid and efficient gain and high milk yield or egg production—goals that differ from the goals of zoo personnel.
Although the NRC requirements are less directly applicable to other species, they can still serve as a useful general reference for evaluating the nutritional adequacy for most birds and mammals. The formulation and evaluation of diets for reptiles and amphibians is even more difficult because there are no domestic animal models and because metabolic rates of poikilothermic animals fluctuate with changes in ambient temperature. Once the nutrient concentrations for the diet have been established, the types and amounts of foodstuffs, methods of presentation, and feeding frequencies should be selected based on the physical and behavioral attributes of the species.
All food should be of good quality. Spoiled or moldy foods, or foods stored for long periods (eg, >1 yr for most bagged feeds and 6–12 mo for most frozen foods) should not be fed. The practice of “topping off” the feed bowl daily or every other day should be discouraged because uneaten food on the bottom can spoil. Food and water dishes should be thoroughly cleaned before adding food or water. Clean, fresh water should always be available to nonmarine species. Trace mineral salt blocks, bricks, or “spools” are commonly offered to ungulates, psittacine birds, and some rodents.
Cafeteria-style feeding is strongly discouraged because captive animals rarely select a balanced diet if given a wide selection of foods. Usually, a nutritionally complete commercial product or in-house mixture that cannot be sorted should comprise the bulk of the diet, with components such as meat, fruit, and seeds comprising only a small percentage. Pelleted diets are especially important with psittacines, to avoid self-selection of calcium-deficient seeds. Muscle and organ meat, fruit, most grains and seeds, and most insects are poor sources of calcium, and excess consumption can result in calcium deficiency. Calcium gut-loading diets containing at least 12% calcium can be fed to insects, or items can be dusted with a balanced calcium-phosphorus powder; however, it is doubtful if enough calcium can be added to the diet. Other sources of calcium include oyster shell, cuttle bone, and ground calcium carbonate tablets.
Obesity is more common than inadequate nutrient intake. Ungulates, primates, and carnivores can rapidly become overweight when excess amounts of a high-quality diet are offered, particularly when activity is limited. In some birds (eg, ratites, waterfowl), rapid growth rates increase the incidence of leg and wing problems. Both adult and growing animals should be routinely weighed to monitor changes.
If a dietary change is contemplated due to suspected nutrient imbalances, deficiencies, or toxicities, the diet currently fed should first be computer-analyzed to assess nutrient concentrations. Ingredient or nutrient changes can then be made based on correcting a suspected or confirmed health problem. For captive, exotic animals, establishing and maintaining dietary histories can be particularly helpful in health assessment. Activity patterns of individuals are also important (eg, atherosclerosis is relatively common in obese birds).
The use of nutritional supplements is popular among animal caretakers. While many keepers and pet owners use nutritionally complete feeds that require no supplementation, supplements are still often provided. Unfortunately, diets are rarely evaluated first to determine which nutrients (if any) are unbalanced. Excessive supplementation of some nutrients (eg, some fat-soluble vitamins, selenium, copper) can be just as harmful as not enough. Diets consisting primarily of cultivated fruits and vegetables may need micronutrient supplementation; however, supplements vary widely in their composition.
The nutrient content of the current diet should be established or estimated first to determine whether any supplement is needed or whether a supplement should be discontinued. If a nutrient is deficient in a diet, a specific supplement in a specific amount should be recommended. The indiscriminate use of supplements should be discouraged because toxicities and nutrient imbalances may result.
Water intake should be assessed routinely but especially in animals with compromised renal function, in lizards or birds prone to gout, and in animals under conditions of high temperature or low humidity in which evaporative losses can be expected. The salt content of water should be known because some species are less tolerant than others. Animals fed dry feeds (pellets, extrusions, hay, etc) require more water than those fed succulent feeds. Potable water should be available ad lib.
Many animals in the wild consume much of their water in the foods they eat. When low-moisture foods are consumed (pellets, extrusions, etc), some animals, depending on how water is presented, may not maintain adequate hydration. Many free-ranging small and tropical lizards receive water from foods and from licking drops that accumulate after rainfall. When in captivity, they frequently do not drink readily from containers. In nature, birds of prey do not drink; however, in captivity, they do drink sometimes.
Humidity may be especially important in maintaining hydration of many reptiles, especially tropical species. Daily misting with warm water is an important source of hydration for some lizards that may not be observed drinking standing water. Eye lesions in semiaquatic turtles (eg, box turtles) and some tortoises may be the result of low environmental humidity (or possibly upper respiratory tract disease) and not vitamin A deficiency. Conjunctivitis may respond better to supportive antibiotic therapy and higher humidity than to supplemental vitamin A. Dietary histories may be especially important in such cases, because many captive turtles are fed commercial cat food that is high in vitamin A.
For a discussion of nutrition for orphaned animals, see Management of the Neonate: Care of Orphaned Native Birds and Mammals.
Last full review/revision July 2011 by Joeke Nijboer, PhD; Teresa L. Lightfoot, DVM, DABVP (Avian)