A healthy diet is of tremendous importance to both humans and animals. Nutritionists and other specialists are gaining increasingly more knowledge about nutrition and its effects on our bodies. The past few decades were marked by a growing understanding among the scientific community that an animal’s diet should not only provide for its nutritional needs, but should also stimulate its natural behaviour. This has prompted the animal kitchen of Antwerp ZOO and Planckendael ZOO to systematically adjust the diets of various animals, in close consultation with the zoo vet and behavioural experts.

FOOD TAILORED TO EVERY SPECIES

When putting together a new diet for a given animal, thought is given to not only its physical health; the animal’s behaviour and emotional well-being are also taken into consideration. Adjustments to an animal’s diet are always carefully considered:

• What does the animal eat in its natural habitat?
• How does its digestive system work?
• What do related animal species eat?
• What were the animals fed at other zoos?

At Antwerp ZOO and Planckendael ZOO, they rely on the expertise of Roxanna van Riemsdijk, animal kitchen coordinator and nutritionist. She puts together well-balanced, healthy and nutritional menus. ‘A good menu should contain just the right amount of proteins, fats, carbohydrates, fibres, vitamins and minerals. If necessary, we systematically adjust this menu to suit the animals,’ she explains. The problem, however, is that the nutritional value of the food eaten by an animal in its natural habitat may differ from the same item available in north-western Europe. ‘The sugar content of a tropical fruit grown in the wild is quite different from that of the same fruit grown around here,’ adds Van Riemsdijk. 

IN THE WORDS OF A NUTRITIONIST: MAINTAINING A GOOD BALANCE BETWEEN NUTRIENTS AND NATURE

In the animal kitchen of Antwerp ZOO and Planckendael ZOO, adjustments are made to specific animals’ diets. These are always made gradually, in consultation with scientist Sara Depauw of Odisee University of Applied Sciences and the relevant zookeepers. Roxanna van Riemsdijk explains: ‘Zookeepers are generally the first to notice the effects of a new diet. Involving them in this process is of crucial importance to obtaining an accurate assessment.’ 

‘Putting together a diet that optimally supports the needs of every animal species is a profession onto itself.’ 

One of the most radical changes in this respect concerns the vegetable diet of the chimpanzees at Antwerp ZOO. Their daily portion of fruit has now been replaced primarily by vegetables, because these contain less sugar. They are still given some fruit every day, but this has been restricted to no more than two pieces per animal. Every day, the primates are given three to four different kinds of vegetables. They get endives, leeks and beets on Monday, and bok choy, broccoli, tomatoes and carrots on Tuesday, for example. Only one type of vegetable is given at each feeding. The pattern is repeated every seven days, resulting in a weekly rotating diet.

Not only is the zoo experimenting with the diet of its primates; browsers such as bongos, giraffes, muntjaks and dikdiks are also being subjected to adapted feed management. In 2021, an entirely new diet was introduced, with completely new products. Today, the zoo is also looking into the animals’ foraging habits (the way they look for food in the wild): animals are given multiple portions during the day, for which slow feeders are used. These foraging spots encourage the animals to feed themselves naturally, just as they would in the wild. Van Riemsdijk explains: ‘This is particularly interesting for ruminants that eat leaves or hay all day long.’ The days of giving animals a big breakfast, which is then eaten too quickly, are long gone. 

Changes in diet are made in conjunction with careful observation of the animals’ behaviour. ‘It’s quite a balancing act, actually,’ says van Riemsdijk. ‘When we adjust an animal’s diet, this always starts with a period of habituation. Whether this concerns primates, giraffes or bongos: we always run tests to see what they do or don’t like to eat. We also take aspects such as portion sizes, feeding times and feeding methods into account. Putting together a diet that optimally supports the needs of every animal species is a profession onto itself.’ 

Whenever changes are made to an animal’s diet, detailed data is collected about the animal concerned. Antwerp ZOO’s dedicated research centre, the Antwerp ZOO Centre for Research and Conservation (CRC), collaborates with students from Belgium’s Odisee University of Applied Sciences. They observe animals’ behaviour, conduct manure tests and perform body condition scores (BSC). Weight is also an important indicator of animal health. Professional scales, tailored to the size of specific animals, are of crucial importance to accurate weight measurements. Keeping systematic records of all types of animal data is paramount in retaining insight into and control over animal health.

IMPACT ON ANIMAL WELL-BEING: MORE THAN NUTRITION ALONE 

Nutrition-related health problems are the main reason for adjustments to animals’ diets. The results achieved among various species show that optimising an animal’s diet contributes to its well-being. Behaviour is a key indicator of animal well-being: zoo animals should exhibit the same behaviour they would in the wild. Regular observations of an animal’s behaviour allow objective records to be made of an animal’s degree of well-being. 

Demonstrable results among the browser population have shown that these animals have become more energetic and exhibit natural foraging behaviour. There is a distinct decline in stereotypical behaviour. Moreover, the switch to a new diet resulted in firmer stools. 

Judging by the initial results, the primates have become calmer and less nervous. Their activity level has increased, they spend more time fleaing one another and demonstrate less aggression towards each other. Thanks to their new diet, the animals can be given larger portions of vegetables to compensate for the fruit they were fed previously, which was rich in sugar. Larger portions also contribute to a reduction in aggression within the group. The animals now spend more time eating, just as they would in the wild.

Future research will teach us if the old adage ‘you are what you eat’ also applies to animals. 

FUTURE RESEARCH: IMPACT ON GUT MICROBIOME

The next phase of the study will examine the impact of the changes in diet on the animals’ gut microbiome (the micro-organisms living in the animals’ digestive tracts). As intestinal bacteria are closely related to nutrition, they can influence behaviour and, though hormone secretion, impact the brain and well-being of an animal. Scientist Nicky Staes, who is involved in this study, will be examining if this really is the case. Staes is a post-doctoral researcher at the Antwerp ZOO Centre for Research and Conservation (CRC) and Antwerp University. ‘All the samples we need have now been taken, and we have conducted behavioural observations. We can now focus on the next phase of our research: analysing the microbiome in the Antwerp University laboratory,’ concludes Staes. She expects the research results to be published in spring of 2024. ‘The research is not limited to the results obtained from the bonobos at Planckendael ZOO. It is a large-scale study in which the gut microbiome of the entire community of bonobos kept at European zoos is being scrutinised,’ explains Staes. In short: future research will teach us if the old adage ‘you are what you eat’ also applies to animals. Want to know more? Read the Science Blog 'Slim bonobos have slim parents'.