The field of zoo and exotic animal nutrition continues to make advances that result in better diets. 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 to hold food, whereas other species obtain or position food using other appendages (or they do not manipulate food). If a commercial extruded pellet is fed, the pieces must be large enough for the bird to grasp easily; pieces should have a diameter of at least 10 mm.
Diets for exotic and zoo animals have been developed through:
food habits in the wild
oral and GI tract morphology
nutritional research on exotic species in the wild and captivity
nutrient requirements established for domestic and laboratory animals and people
anecdotal literature reports (eg, case studies)
physiologic status of the animal (eg, young, old, pregnant, etc)
The ultimate criteria to evaluate 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). Nutritional guidelines have also been set up by specialist exotic nutrition animal groups (eg, specialist groups from zoological organizations). Not all anecdotal nutritional information is scientifically verified, and if this information is used it should only be done by specialized professionals such as exotic animal nutritionists.
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 minimal amounts and 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 those for housing zoo animals. In zoos and other exotic animal collections, a maintenance diet should be fed in general, although a breeding or other specific diet may be needed sometimes, depending on the animal and circumstances.
Although the NRC requirements are less directly applicable to other species, they can still serve as a useful general reference to evaluate 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 year for most bagged feeds, 3 to 6 months for pellets, and 6–12 months 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 non marine 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.
To improve consumption of pelleted diets, feeding should be done in the morning, with the other food items offered during the day. All diet items to be fed should be weighed, and the actual intake recorded.
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%–15% calcium should be fed to insects. Dusting with a balanced calcium-phosphorus powder is also a possibility; however, it is doubtful this can add enough calcium 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 weighing four times a year is not possible, a body score index should be performed.
If a dietary change is contemplated because of 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).
To prevent "diet drift" (changes in the diet consumed because it is not regularly weighed), dietary intake (weight of feed minus leftovers) should be determined at least 3 times a year.
A body condition score and fecal score should be also be recorded 3 times per year by the animal keeper and two independent experts, such as a veterinarian and a nutritionist. The general status of the animal (pregnant, old, sick, etc) should also be recorded.
The use of nutritional supplements is popular among animal caretakers. Although many keepers and pet owners use nutritionally complete feeds that require no supplementation, supplements are still often provided. 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. Unfortunately, diets are rarely evaluated first to determine which nutrients (if any) are unbalanced.
If a nutrient is deficient in a diet, a specific supplement in a specific amount should be recommended. Excessive supplementation of some nutrients (eg, some fat-soluble vitamins, selenium, copper) can be just as harmful as not enough because of toxicity and nutrient imbalance. Diets consisting primarily of grain products and cultivated fruits and vegetables may need micronutrient supplementation; however, supplements vary widely in their composition.
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, depending on the circumstances, so clean drinking water must be available at all times.
Humidity may be especially important to maintain 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 food, which is mostly cat food high in vitamin A.
Also see a discussion of nutrition for orphaned animals.