The Diet Detective: How Do Animals Eat, Part I

I thought it would be interesting to find out more about the way animals eat, so I reached out to Bruce Rengers, Ph.D., R.D., a professor at Metropolitan State College of Denver and a former zoo employee, and Jennifer Watts, a nutritionist at the Brookfield Zoo in Chicago. Here's what I learned:

What are common weight-gain issues that animals share with humans?

Bruce Rengers: Some—but certainly not all—animals, when they are sedentary and have easy access to food, such as in a zoo, definitely do become obese. The best example I have seen is orangutans. In the wild they are arboreal animals that move over large distances. It is hard to replicate that lifestyle in a zoo, so orangutans become obese and sometimes develop Type II diabetes. I did not observe this with gorillas, however, even though the zoo gorillas lived in exactly the same type of environment and had the same food. There were other animals that were obese or overweight in the zoo, and we spent time making special diets to help them lose weight.
There is a concern in zoos about what animals eat. People always want to feed zoo animals or pets the kinds of "seductive" foods we eat as humans. Feeding animals highly refined, sugary, fatty human foods (or natural foods that are high in fat) can cause them to start rejecting their normal foods. There is, for example, concern about giving birds nuts and seeds that are very high in fat because they will then start rejecting their normal seeds and other foods that are not so high in fat.
How often do animals eat? I'm sure all animals are different, but is there an overall theme or pattern?

Jennifer Watts: Most animals are fed twice a day. Animals with faster metabolisms (passerine birds, for example) must have food throughout the day, while animals with slower metabolisms (snakes, alligators, etc.) eat only once or twice per week, or even every other week. Ruminants (camels, giraffes, bison, cattle, etc.) cannot be offered one grain meal per day; it must be spread out to two or three meals to avoid rumen acidosis. They must also have access to hay or grass most of the day to maintain rumen health.

For most carnivores we institute a "fasting day" or "bone day" when they don't get their normal amount of food. This strategy replicates the way the animals would eat naturally. Most zoos, however, cannot duplicate true natural feeding—i.e., feeding a lion 30 pounds of meat then letting it fast for five to six days—because this would not provide consistent behavior from the animal for training and evacuating.

We need most animals to evacuate reliably so that keepers can clean the exhibit, remove the animal from the exhibit to do a physical/visual check and examine the exhibit. Any animal that needs to move from its exhibit area to a behind-the-scenes holding area usually has the "good stuff" saved for its evening meal, because if the animal knows that it's going to get something good afterwards, it will be more compliant about moving inside.

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