Providing an optimal diet for wild animals in captivity is a crucial element of animal husbandry and can have beneficial effects on an animal's health, reproductive success, and welfare. Although considerable developments have taken place in the field of zoo animal nutrition, providing a nutritionally balanced diet to a variety of taxonomic species remains challenging.
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 these large birds to grasp easily; pieces should have a diameter of at least 10 mm.
Diets for exotic and zoo animals have been developed based on a variety of sources:
practical experience
feeding ecology in the wild
oral and GI tract morphology
nutritional research on exotic species in the wild and in captivity
nutrient requirements established for humans, livestock, and domestic and laboratory animals
anecdotal literature reports (eg, case studies)
physiological status of the animal (eg, young, geriatric, pregnant)
body condition score
wild feeding behavior and activity budgets
The ultimate criteria to evaluate a diet's suitability for a given species are growth, reproductive success, and longevity.
The minimum nutrient requirements established by the NRC for domestic and laboratory animals can be useful starting points in setting target nutrient levels for an exotic species. For example, Nutrient Requirements of Small Ruminants, published by the NRC, contains nutritional information on cervids (white-tailed deer, red deer, wapiti, and caribou) and camelids (llamas and alpacas). However, for some species, domestic animals and livestock remain poor models, and comparison with exotic animals in their natural habitat provides a better baseline. Nutritional guidelines have also been set up by specialist exotic nutrition animal groups (eg, 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.
Dietary requirements established for ungulates, mustelids, canids, felids, rodents, primates, lagomorphs, gallinaceous and anseriform birds, and fish can be used to formulate diets that meet nutritional requirements for exotic species with closely related domestic counterparts. However, nutrient requirements established by the NRC represent minimal amounts used only as guidelines, because the goals of livestock producers include rapid and efficient gain and high milk yield or egg production—goals that differ from 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 no domestic animal models exist and 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 and foods stored for long periods (eg, > 1 year for most bagged feeds, 3–6 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 nonmarine species. Trace mineral salt blocks, bricks, or “spools” are commonly offered to ungulates, psittacine birds, and some rodents.
Cafeteria-style feeding (free choice among a range of food items) 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 an 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. With psittacines, pelleted diets are especially important to avoid self-selection of calcium-deficient seeds.
Consumption of pelleted diets is increased by feeding in the morning and offering other food items 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 of these items can result in calcium deficiency. Calcium gut-loading diets containing at least 12–15% calcium should be fed to insects. Dusting insects with a balanced calcium-phosphorus powder before offering them as a meal is also a possibility; however, it is doubtful that dusting in this way adds enough calcium to the diet to meet most animals' nutritional needs. Other sources of calcium that can be offered to meet nutritional needs include oyster shell, cuttlebone, and ground calcium carbonate tablets (see also Nutrition in Reptiles).
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 a minimum of 4 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. Documenting activity patterns of individuals is also important (eg, atherosclerosis is relatively common in obese, typically inactive birds).
To prevent "dietary drift" (unapproved and gradual alteration of an animal's diet), dietary intake (weight of feed minus leftovers) should be determined at least 3 times a year. In addition, diets should be modified by appropriate staff, such as a specialized nutritionist or veterinarian.
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. Body condition and fecal quality scores vary by species. Each animal's score is assessed against an optimal body condition (from emaciated to obese) or fecal condition (scored on stool consistency) for that species. The general status of the animal (pregnant, old, sick, etc) should also be recorded.
Dietary management, however, requires more than formulating a nutritionally balanced diet. Knowledge of an animal's feeding behavior and activity budget is required to help ensure appropriate zoo management of a particular species. Mimicking aspects of natural feeding behaviors (eg, feeding whole prey to carnivores) is important to improve dietary management and hence animal welfare.
In that many zoological institutions are concerned about their role in climate change, food items fed to animals should be closely monitored to minimize waste, use of (natural) resources, and carbon footprint. Therefore, optimal diets for exotic animals should be developed according to not only nutrient requirements but also sustainability. Sustainable practices can be established, such as using local and seasonal food items and taking a critical look at transportation. Similarly, the role of palm oil or soy in complete diets should be closely investigated.
Nutritional Supplements for Exotic and Zoo Animals
Within the history of zoo animal nutrition, supplements have been widely used to complement unbalanced diets fed to exotic animals in human care. Nutritional supplements are popular among animal caretakers and often thought to be essential in providing a nutritionally balanced diet in terms of vitamins and minerals. Often, food items are believed to be deficient; meat, fish, or insects are dusted with high-mineral powders with the assumption that the risk of health issues or reproductive failure will be minimized. Although many keepers and pet owners use nutritionally complete feeds that no longer require supplementation, supplements are often still provided. The nutrient content of the current diet should be established or estimated first to determine whether a supplement is needed or should be discontinued. If a nutrient is deficient in a diet, a specific amount of the required supplement should be recommended. Excessive amounts of some nutrients (eg, some fat-soluble vitamins, selenium, copper) can be just as harmful as insufficient amounts due to potential toxicity and nutrient imbalance.
Supplements are mainly used to complement diets of carnivores, piscivores, and insectivores that are fed dead, frozen prey items. For instance, piscivorous animal species fed frozen fish in human care require supplementation of vitamin E and thiamine. In addition, diets for carnivores can be customized with products designed to supplement meat, either with or without bones.
To prevent over- or underdosing and subsequent nutrient toxicity or deficiency, animal caretakers should create diets based on weight, rather than on a set predetermined amount, of a vitamin or mineral supplement.
Water for Exotic and Zoo Animals
Water intake should be assessed routinely, especially in animals with compromised renal function, lizards or birds prone to gout, and 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 of higher salinity 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 for all species.
Many animals in the wild fulfill much of their water requirement from the foods they eat. When animals in captivity consume low-moisture foods (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. In captivity, they frequently do not drink readily from containers. In nature, birds of prey do not drink but instead get their hydration from the meat in the prey they consume; 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 (eg, by an automatic misting system) could be an important source of hydration for some lizards that may not be observed drinking standing water. Eye lesions (or possibly upper respiratory tract disease) in semiaquatic turtles (eg, box turtles) and some tortoises may be the result of low environmental humidity and not always a result of vitamin A deficiency. Conjunctivitis may respond better to supportive antimicrobial treatment 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 often cat food high in vitamin A.
Also see a discussion of nutrition for orphaned animals.
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