“FORMULATING DIETS FOR POLAR BEARS IN CAPTIVITY”
Barbara Lintzenich, Daniel F. and Ada L. Rice Conservation Biology and Research Center, Brookfield Zoo, Brookfield, IL 60513.
Ann Ward, Nutritional Services Department, Fort Worth Zoo, Fort Worth, TX 76110
Amy Hunt, Nutritional Services Department, Fort Worth Zoo, Fort Worth, TX 76110
Development of a nutritionally complete diet for polar bears in captivity includes consideration of: feeding ecology, gastrointestinal tract characteristics, species specific requirements, known requirements of domestic models, physiological state, environment/management considerations, and the foods available. Researching these categories and compiling data will allow the best diet in captivity to be offered.
The polar bear, the most carnivorous of the Ursidae family, prey primarily on ringed seals (Best, 1985; Derocher, et. al, 2000; Stirling and Archibald, 1977). Other seal species (bearded, harp), some whale species (white, narwhal), walrus, reindeer, sea birds, carrion, and vegetation have been reported as consumed (Derocher, et. al, 2000; Derocher, et. al, 2002; Knudson, 1978; Russel, 1975; Smith and Sjare. 1990). Consumption varies depending on the season and location. Some bears prey on seals year round as long as the ice has not receded (Derocher et. al, 2002). In locations where ice recedes some bears may be restricted to land for periods as long as 6 months where food is limited (Knudsen, 1978). Though bears prefer the energy rich blubber of seals, whole carcasses still contribute to the overall diet and may be especially important to subadults and orphaned cubs (Stirling, 1974).
The stomach of Ursidae is simple; the distal segment of their intestine is marked only by an appearance of mucosa with no cecum present (Stevens and Hume, 1995). Similar to other carnivores, polar bears have high digestibility coefficients for protein and fat, (Best, 1985). Their simple digestive tract is well suited for their highly digestible diet. No species-specific requirements are known for polar bears. Controlled studies necessary to determine the requirement for a specific nutrient are difficult to conduct with many captive wild species. However, energy requirements have been estimated and appear to be lower than those of large cats (Best, 1985). Other research has shown that although polar bears have higher vitamin A stores than other species (Leighton, 1988), this does not necessarily indicate a higher requirement for vitamin A. High vitamin A stores may be an adaptation to the high level of vitamin A in the natural diet. Since controlled studies have not been conducted, serum nutrient parameters collected from healthy free-ranging animals may provide data from which to assess captive animals (Kenny et. al., 1998). Additionally, a database on these levels in healthy captive animals can be useful in assessing diet adequacy (Crissey et al., 2001). (When assessing serum nutrient data it is important to consider if nutrient then reflects stores or diet recently ingested, sample size, appropriateness of methods, seasonality of samples, and diet ingested.
Due to the lack of species-specific data, it is reasonable to consider the known requirements of related domestic animals. Domestic models have been studied in great detail, and thus provide a database from which to extrapolate. A range of probable requirements can be established for polar bears based on animals with similar feeding ecology and gastrointestinal tracts. Domestic cats and dogs are used as models for polar bears (NRC, 1986, NRC, 1985, AAFCO 1999). Cats are considered strict carnivores and dogs omnivores. Polar bears are primarily carnivorous with vegetation as a minor portion of the diet (Knudson, 1978; Russel, 1975). Consequently a range of nutrient levels encompassing both feeding strategies is appropriate for formulation of captive polar bear diets.
Physiological state of the polar bear is another consideration in diet formulation. Captive diets can be tailored for pregnant, growing, lactating, thin, or obese bears. Diets also can be assessed for seasonal changes. Management considerations (training, group feeding/competition, exhibit design/enrichment) should be factored into the diet to ensure consumption of a nutritionally complete diet. The diet items polar bears consume in the wild are not available for feeding in captivity. The nutrient content of the natural diet, if appropriate considering captive conditions, can be mimicked with items available to zoos. It is the nutrients, not the package they come in, that should be considered. Various food items such as nutritionally complete foods, meat mixes, marine products and produce, when fed in combination, should result in nutrient levels that meet the probable requirements. Nutrients in items that are commercially available may vary depending on the location and time of year. Fish is often a large part of many polar bear diets. The nutrient content of fish can vary greatly (Bernard et al., 1997). Consequently, regular analysis of diet ingredients and diet review are imperative to offering appropriate diets.
As directed by the BEAR TAG, a survey of diets offered and consumed by captive polar bears across seasons took place from 1996 -- 2000. The survey was completed by seven zoos. It involved a bear data sheet, a questionnaire and a four day intake study. The bear data sheet asked about age, sex, weight/body condition, and physiological state. The questionnaire asked about enclosures, environments, health (example - coat condition), and stool quality. The four day intake study involved weighing the food in and food out each day in order to compare intake to offered. The survey revealed a large range in diets consumed and consequently nutrient levels. Nutrients levels consumed across seasons overlapped. Thus the overall mean across all seasons is presented. Nutrient content of diets consumed on a dry matter basis was (mean ± standard deviation) 42.08% ± 9.05 crude protein, 3.31% ± 1.51 crude fiber, 19.29% ± 6.34 crude fat, 2.20% ± 0.63 calcium, 1.46% ± 0.19 phosphorus, 31.60 IU/g ± 18.37 vitamin A, 2.83 IU/g ± 1.33 vitamin D3, and 271.65 mg/kg ± 96.99 vitamin E. Most diets consumed met or exceeded the probable nutrient range for captive polar bears. Study animals have good coat condition. Stool condition varied from well-formed to soft.
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