New insights into dietary management of polar bears (Ursus maritimus) and brown bears (U. arctos)

Abstract

Although polar bears (Ursus maritimus) and brown bears (U. arctos) have been exhibited in zoological gardens for centuries, little is known about their nutritional needs. Multiple recent studies on both wild and captive polar bears and brown bears have found that they voluntarily select dietary macronutrient proportions resulting in much lower dietary protein and higher fat or digestible carbohydrate concentrations than are currently fed in most zoos. These lower protein concentrations selected by both species maximized growth rates and efficiencies of energy utilization in brown bears and may play a role in reducing kidney, liver, and cardiovascular diseases in both species. Therefore, we propose the need for the development of new dietary regimens for both species in managed care that better reflect their macronutrient needs. We developed a new kibble that is higher in fat and lower in protein than typical diets that have been fed in managed care, has a fatty acid profile more consistent with wild bear diets, and has been readily consumed by both brown bears and polar bears. The kibble can be fed as the sole diet or as part of more complex diets with additional fruits, meats, or vegetables. Because many nutritional deficiencies and related diseases can take months or years to appear, we urge caution and continued long‐term monitoring of bears and their diets to ensure their optimal health.

Ursids evolved early and continuously to be low-protein macronutrient omnivores

“…3 ). In evaluating if either one of those might be more suitable for sloth bears, the protein ME ratios of ursid milks and the diets voluntarily selected by brown bears, polar bears, giant pandas, and sloth bears are low and do not differ from each other (t (3) = 2.449, p = 0.092), which minimizes maintenance energy requirements and maximizes the efficiency of gain 1 , 3 , 4 , 29 , 40 (Table 1 ). Additionally, brown bears and sloth bears prefer high fat, low carbohydrate diets when given a choice between foods rich in either carbohydrates or fats 3 (Table 1 , Fig.…”

“…This suggestion has been followed by numerous authors 22 , 28 who have recommended dietary fat be kept to a minimum and, therefore, diets be high in carbohydrates. The second hypothesis, excess dietary protein, was recently proposed as causing the high incidence of hepatobiliary cancer and kidney disease in captive polar bears 4 , 29 . Nevertheless, in the absence of data on sloth bear nutritional requirements, the nutritional standards for the dog, cat, mink and fox have been recommended for developing captive sloth bear diets (i.e., high protein, low fat diets) 28 .…”

Serum plays an important role in reprogramming the seasonal transcriptional profile of brown bear adipocytes

“…All procedures were approved by the Washington State University Institutional Animal Care and Use Committee (IACUC) under protocol number ASAF 6546. The bears were fed a pelleted, high-fat diet specifically formulated to meet the macronutrient needs of brown bears ( Robbins et al., 2022 ) and allowed to graze on highly palatable, abundant and nutritious white clover ( Trifolium repens giganteum ) and grasses (e.g., Poa pratensis , Phleum pratense , and Bromus gracilis ) in a 0.56-ha exercise yard ( Rode et al., 2001 ). The bears were fed twice daily during the active season, from mid-March to mid-October.…”

Label-Free Quantification (LFQ) of Fecal Proteins for Potential Pregnancy Detection in Polar Bears

“…Bears were born in a zoo ( n = 6) or were wild orphans that had been brought into a zoo as cubs ( n = 4) and ranged in age from 5.2 y to 15.9 y at the time of sample collection. Diets varied by institution, by season, and likely even within institution by day, but generally were composed of raw meat, fruits and vegetables, dry pellets formulated for feline or canine [ 44 , 45 ], and enrichment items, such as ox tail or live fish.…”