An animal's diet can tell a lot about how that animal lives, from its high-traffic feeding locations to its preferred type of food. These complex dietary strategies have evolved over time and have been specialized to meet each animal's needs.
Wild polar bears’ (Ursus maritimus) diets contain low protein marine fats, which polar bears have optimized to supply them with the metabolic energy needed to survive in their harsh environment and live to their maximum lifespan of the mid to late 30s or early 40s.
Sadly these natural dietary strategies are not used for captive polar bears. Since polar bears are classified as carnivores, their prescribed diets closely resemble those of domesticated dogs and cats. These diets consist of dry pellets, raw meats, and whole prey and lack the low-protein marine fats commonly consumed by wild polar bears.
Rode et al. compared the macronutrients of 14 captive polar bear diets to show the differences between the wild and captive polar bear diets. They found that ten of the 14 polar bear diets had either equal to or more than double the amount of protein compared to wild polar bears on average.
This change in diet has had some hypothesized negative consequences for captive polar bears. Studies have shown that in the United States, 64% of all polar bear deaths below the age of 30 were related to cardiovascular, renal, and liver diseases and cancer.
Scientists have theorized a link between the excess phosphorus and nitrogen in bile extracted from captive bears and the increased cases of renal and liver diseases and cancers. This same link can be seen in other animals like humans.
While this looks grim for captive polar bears across the nation, researchers at the Washington State University (WSU) Bear Center have shown that natural dietary strategies have not been lost in captive polar bears.
Feeding trials were conducted to show the preferred feeding habits of captive polar bears. In these trials, both protein-rich raw meat commonly found in the captive polar bear diet and lard to simulate the marine fat found in wild polar bear diets were placed side by side, and the captive polar bear preferred the low protein high-fat lard over the high protein raw meat. These food trials showed that captive polar bears still have the dietary specializations of wild polar bears.
With this new insight into captive polar bear diets, WSU Bear Center researchers devised a dietary approach to get the captive polar bears the nutrients needed. The researchers created a dry kibble consisting of 23% protein, much closer to the 18% consumed by wild polar bears.
While more tests of the new kibble are needed to make a conclusive answer on if the dietary changes help polar bears, the dietary change is definitely an option that zoos around the United States should consider the next time they feed their polar bears.
