Protein and Fat Consumption of Zoo Polar Bears in 14-day Ad Libitum Trials, 2019-2020

Fourteen-day macronutrient selection trials were conducted with 9 polar bears (5 males and 4 females) in cooperation with 6 U.S. zoos. Bears were given the opportunity to consume either lean meat (e.g., lean beef, horse meat, or a low fat commercial canine diet such as Nebraska Premium Canine) or fat (e.g., lard or trimmed beef or pork fat) presented in separate piles ad libitum during 2 to 3 feedings per day. A 4-day dietary adjustment period occurred prior to each 14-day trial during which each bear was given increasing amounts of both foods. By the 3rd or 4th day of the adjustment period, the amount offered was increased to ad libitum such that surplus food was still available at the end of each meal. Each bear was weighed prior to their first feeding of the 14-day trial and before feeding on the morning following the last day of the trial. All food offered and rejected were weighed each day to determine the total amount consumed. Samples of each food were collected throughout the study and stored frozen immediately after collection and during shipping to Washington State University for nutritional analyses.

Samples were freeze-dried to determine dry matter content, and ground and analyzed to estimate crude protein content (N X 6.25) via a nitrogen-carbon analyzer, fat content by ether extraction, and gross energy content by bomb calorimetry (Erlenbach et al. 2014). Carbohydrates were not measured because meat has < 1% soluble carbohydrates. Digestibility of fat and energy were estimated as 99% and 97%, respectively (Dyck and Morin 2011). The metabolizable energy content of each bear’s selected diet was calculated by multiplying the total dry matter amount of protein and fat consumed during the 14-day study by the Atwater specific factors of 4.1 kcal/g protein and 9.0 kcal/g fat (Erlenbach et al. 2014).