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How It's Done: Zoo Nutrition


Dr. Jennifer Watts loves animals and math. In her work as the director of nutrition at the Chicago Zoological Society’s Brookfield Zoo, both passions are important.

There are about 3,000 animals at the zoo, all with unique personalities, preferences and dietary needs. To feed them the right macronutrients and micronutrients, it takes some serious math and planning. And to make sure the diet is appealing, diverse and enriches their lives—that's a labor of love.

This interview has been edited for clarity.  

My job is to design the diets for our animals. I do the science behind the nutrition. We start by looking at what animals eat in the wild using information provided by researchers in the field. Based on that, we determine the composition and nutrient concentrations that will be the best for our animals’ health.

Take a nutrient like protein. We know that for primates, protein is about 10 to 15 percent of the diet. But for some species, like lorises or other animals that eat gums or nectar, the protein requirements might be a little bit lower.

There’s some trial and error. We'll try a diet and see how it works. If we see any deficiencies or anything that that’s not quite right, we make changes as we go. Zoo nutrition is still a new field, and we're learning every day.

Designing a Diet

When I started working here, the brown bears were not at an ideal weight. I needed to focus on reducing their weight. Part of the problem was that the proportion of nutrients in their diets wasn’t changing seasonally in the way that it would for bears in the wild.

In the spring, when brown bears come out of their dens, they eat a lot of grasses. They might eat the carcass of a calf if they find one, but their diet at that time of year has a lot of plant matter and very little protein.

As the year progresses, the protein content increases, culminating in the salmon runs where brown bears eat as much salmon as they possibly can to fatten up. Later in the fall, they focus on berries, nuts, seeds, grasses and other plants.

To reflect these seasonal changes, I put them on a diet that has changes in the proportion of nutrients—not just the overall volume of food—throughout the year.

Other animals have different seasonal changes in their diets. For hoof stock, we change their diet at the start of the wet season in May to simulate the way that wild grasses would be more lush and full of sugar during that time of year. For primates, we simulate a fruiting season by adding lots of fruit and vegetables to their diet, resulting in a 20 percent increase in calories during spring.

But there are limits. In the wild, bears eat fungus, so we were excited about giving them different mushrooms. But they were just kind of like, "no, no, don't want it." Same with cranberries. Sometimes it's like feeding 3,000 toddlers.

Supplying the Food

We get our fruits and vegetables from the same vendors that supply restaurants and grocery stores. We try to source as locally as we can, using local vendors who themselves source as locally as possible. We use about 5,000 pounds a week. 

We limit the amount of fruits and starches. Domesticated fruits are much higher in simple sugars than, say, a wild fig or a wild apple would be, and animals are too efficient in metabolizing those sugars and often turn them to fat.    

For some of our animals, like the marine mammals, we use whole fish. We acquire seven or eight different kinds, ranging from herring that are about 10 inches long to silversides that are two or three inches. Some species can only be caught once a year, so we have to order a whole year's worth and keep it in cold storage offsite. We go through about 180,000 pounds of fish a year.

We also get insects. Crickets, meal worms, earth worms. We even get whole prey, like mice, rats and rabbits.

And then we also use feeds—specially manufactured nutritionally complete foods, like dog food—usually in the form of extruded pellets or biscuits with added vitamins and minerals. This helps us get the right amino acids, fatty acids and micronutrients to our animals.

There are vitamin and mineral supplements, too. We don't like to hide pills in food when we can avoid it. We prefer to find things that the animals will take readily, so we'll use gummy vitamins or chewable children's vitamins, just like you'd get from the grocery store.

We also have what we call enrichment items. These are things that can make our animals' lives a little more interesting and exciting. For carnivores, this includes things like rawhide bones and pigs' ears.

And, we like to encourage species-specific behaviors. For example, with the echidnas we’ll create foraging opportunities for them. We'll spread food around the habitat—it could be rice, seeds, nuts, raisins or even breakfast cereal that you might have in your own pantry. That way, foraging animals can use some of their awake time to look for food here like they do in the wild.

Accounting for Taste

We have over 350 species here at Brookfield Zoo, with more than 2,500 individual animals. And each animal is an individual. They all have their own taste buds and likes and dislikes. We tailor the diets not just for the species, but for the individuals within the species.

In some species those individuals can be especially picky. We had five binturongs and none of them would eat the same thing. One of them liked peppers, one of them didn't. One of them liked strawberries, one of them didn't.

I know just about every animal's name here at the zoo. To design diets for the animals, I have to know what they prefer and where they are in life. Are they young and active? Are they geriatric? Are they lactating? These things influence their nutritional needs.

And variety is important. If you had to eat the same thing every day, you'd get tired of it fast. So would our animals. We give them as much variety as possible. Today we're preparing watermelon, tomato, white pepper and green leaf for our rhinos, but tomorrow it will be grapes, sweet potatoes and butterhead.

We had a few diabetic monkeys who were being fed the exact same diet every day to minimize blood sugar spikes. But they were bored with it, and psychological health is as important as physical health. I came up with a chart that showed how a wider variety of foods can provide the right level of carbohydrates for them. It was great to hear how excited they were the first time they received  strawberries.

That’s one of the things about this job that’s really satisfying. I'm helping animals live their best lives. And seeing healthy, happy animals can get people more interested and involved in conservation. It’s so great to walk around the zoo and see visitors who are amazed by these animals.

The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.