Nutrition in Zoo Carnivores

Nutritional requirements for captive carnivores historically have been based on dietary knowledge derived from the pet food industry. Because nutrition-related health problems are still common in captive carnivores, dietary management, including feeding practices, has become a subject of increasing interest. For instance, feeding whole prey versus processed meat has been shown to improve oral health and encourage natural feeding behavior.

Most zoos in the US use nutritionally complete commercial diets to feed exotic felids, canids, mustelids, and viverrids rather than attempt to prepare diets in-house. In other parts of the world, feeding whole prey (eg, cows or horses) is a more common practice. Fresh and thawed pig meat may contain a virus that can cause pseudorabies (Aujeszky disease) when it is fed raw. Contaminated meat or meat adulterated with medicines or other drugs and bacteria should not be fed. Meat and meat products should be of the same quality as those intended for human consumption. Other prey animals, such as rabbit and chicken, are also regularly offered.

A supplement containing, at a minimum, calcium, vitamin A, iodine, taurine, and some B vitamins should be added to the meat diet. Feeding a complete mixed diet greatly decreases incidence of nutritional problems in captive exotic carnivores; however, such a diet regularly causes diarrhea. Most commercial diets are based on horsemeat and its by-products; however, diets based on beef and poultry are also available. Typical lesser ingredients include fish meal, soybean meal, beet pulp, and ground corn, as well as mineral and vitamin supplements.

Exotic felid diets are usually higher than canine diets in fat, protein, and vitamin A. A diet suitable for most cat species contains 45–50% protein, 30–35% fat, 3–4% crude fiber, 1.2–1.5% calcium, 1–1.2% phosphorus, and 20,000–40,000 IU of vitamin A/kg diet (dry-matter basis). These diets are primarily based on guidelines from the NRC or European Pet Food Industry Federation. Apparently, exotic cats, like domestic cats, are unable to convert carotene to vitamin A, tryptophan to niacin, and linoleic acid to arachidonic acid. They also probably cannot synthesize adequate taurine (taurine deficiency has been reported in leopards) and would be susceptible to ammonia toxicity if fed an arginine-deficient diet (1). Therefore, these nutrients should be considered dietary essentials for all felids.

Because wild felids are obligate carnivores, captive exotic felids are typically fed an exclusively carnivorous diet. However, whereas the beneficial effect of plant fiber on the metabolism of domestic cats has been described (2), the positive effect of the role of animal fibers (eg, fur, bones, feathers, or tendons) as a source of dietary fiber in felids has received less attention. A beneficial effect of animal fibers on fermentation has been observed in captive cheetahs, suggesting that feeding whole prey might be essential in promoting gut health and thus overall animal health (3).

Frozen and canned cat foods usually are more palatable than dry ones to exotic cats. Many zoos prefer to use frozen diets over canned products, because generally they are less expensive and large quantities are easier to feed. The soft, hamburger-like consistency of commercial diets can result in excessive calculus deposition on teeth and periodontal disease if hard or unprocessed items are not also provided. All cats fed a soft diet should receive bones with some meat intact twice weekly. Horse or beef shank bones are suitable for large cat species; oxtails, rib bones, or whole rodents can be used for smaller cats. Mice, rats, and chicks are frequently included in the diets of smaller cats. Rodents, poultry, fish, and organ and chunk muscle meats can be offered as occasional treat items to administer medication or to stimulate appetite, but generally they are not required as dietary staples for large cats fed commercial diets.

Canids can be fed frozen, canned, or dry canine diets. Although most canids are less particular than cats, frozen and canned foods are generally preferred over dry ones. Bones should be included in the diet when soft foods are fed. Canids can also be fed meat, with the right amount of vitamins and minerals added, varied with small prey animals like rats, mice, rabbits, and chickens. Small amounts of fruits and vegetables can be included in the diets of foxes and coyotes.

Most mustelids and viverrids do well on frozen feline diets or canned cat foods; a meat-based diet supplemented with the right amount of vitamins and minerals is also appropriate. Many species readily accept small amounts of fruits, vegetables, and cooked egg. Mice, fish, and chicks can be offered as occasional treat items and to stimulate appetite and activity. Rib bones can be given twice weekly to promote dental health. Canned foods may be more palatable but are not recommended as a base diet because ferrets may not be able to eat enough of them to meet their calorie and protein needs.

Procyonids can be fed diets similar to those offered to small canids, or an adequate meat diet can be fed. Feeding a good-quality dry dog food or omnivore pellet, supplemented with vegetables, helps minimize obesity problems that commonly result when frozen or canned diets are fed. The red or lesser panda has been maintained successfully on commercial high-fiber primate biscuits and bamboo. The herbivorous food habits of the giant panda require large amounts of bamboo supplemented with high-fiber primate biscuits.

Bears can be fed meat supplemented with vitamins and minerals, frozen canine diet, dry dog food, fish, and/or commercial omnivore biscuits. Polar and Kodiak bears do well on a diet of 25% frozen canine diet, 25% fish (eg, smelt), 15% dry dog food, 15% omnivore biscuits, and 20% vegetables as enrichment (4). Commercial diets formulated especially for polar bears are available as well. Primarily herbivorous bears, like spectacled, sun, sloth, and black bears, should be fed a high-fiber pellet, combined with (green) vegetables and, preferably, browse (leaves, bark, and branches). Seeds and nuts can be used as enrichment, as long as their energy density is accounted for as part of the total energy provision per day. Other bear species can be fed less fish and more omnivore biscuits, bread, and produce. Food intake of captive bears varies widely with the season. Intakes generally are maximal during summer and early autumn and minimal during winter. Feeding extra cod liver oil (0.5–1 L) to polar bears is advisable before their hibernation starts.

The importance of not only what is fed to captive carnivores to ensure they receive a nutritionally balanced diet but also how this diet is fed has become a topic of concern. Mimicking feeding behavior in the wild appears difficult, as feeding strategies for captive carnivores differ between institutions. Some of the differences in feeding strategies include (number of) fasting days, whole prey versus carcass versus processed meat feedings, hunting success, number of feeding methods used, social cooperative feeding methods, etc. Reassessing feeding regimens in the management of captive carnivores, and therefore incorporating strategies that more resemble the natural situation, might promote more natural behavior and overall health.