Chopping Up the Science of Food Presentation

James Brereton is a lecturer at University Centre Sparsholt. He has investigated behaviour and enclosure use for a range of zoo-housed animals. He also sits on the BIAZA native species working group and acts as a typesetter for the EAZA publication JZAR (Journal of Zoo and Aquarium Research).

The Morning Feed Round

Imagine you’re a member of an animal care team. It’s 8:21 in the morning, and you’ve just started your shift at a facility such as a zoo or animal sanctuary. Your animals need to be fed before today’s visitors enter, and you’ve been put on food preparation duty. Staring up at the mountain of fresh apples, mangos and carrots that need to be sliced, you begin to feel like a sous chef in the kitchen of some famous restaurant. Your customers – the animals, are waiting. The bears are grunting like an impatient couple, the monkeys are chittering like unruly kids and the parrots – well, they’re squawking like a bad google review waiting to happen. Looking at the pile of food that needs to be processed, you may well be wondering why it all needs to be chopped, blended or deyolked. Much like the pear you’re currently chopping up, let’s break this question down into manageable chunks.

Animal Behaviour and Welfare

It’s all about the animals, ultimately. You want to make sure they get a diet that is nutritionally suitable, and that also allows them to engage in natural behaviours. That can be a real challenge.

In the wild, for example, your gibbons might be eating over 100 different plant types. In your zoo, you have a grand total of twelve food types. So, to keep your animal’s lives interesting, you give them as much variety as possible. This often means you need to chop the food up into bits – you can’t give a whole pineapple for example. Small amounts of many different fruits and vegetables should allow your animals to have choice and a healthy diet, right?

Not always. For some species, selective feeding comes into play. Many animals are motivated to seek out the highest calorie, lowest fibre food item available, often for the lowest amount of effort. This concept, coined optimal foraging theory, is why we tend to go for pizza instead of salad, and why take-aways that deliver to the door tend to get good business. For our animals, the reality may be that we give them a healthy diet, but they selectively eat the unhealthy parts.

You may also be chopping food to reduce aggression for your animal colonies. In theory, chopped food items can be more easily shared by an entire group.

While this makes logical sense, the evidence on food aggression is more complex. For macaques and coatis, whole food actually reduces aggression. When given large food items, these animals tend to carry their food to a quiet corner where they eat by themselves, without aggression. This compares to the normal scenario, where individuals cannot carry their food away because each food item is too small to be worth the movement. Just don’t drop a couple of food items at a time for a large colony of animals!

The situation is complex, however. For mangabeys, for example, whole fruit is associated with greater food stealing, and salmon spit their food out more often if it is too big! Clearly, there is no one-size-fits-all rule. But there is a need for evidence. Finding out what size of chopped food is useful information – it’s likely that a starling will need a much finer chop than a tapir!

In the wild, animals would not receive their food chopped up into bitesize morsels, so evolution has equipped species with tools for food processing. Fruit-eating birds like hornbills, for example, have been observed bashing unripe fruit against branches to soften the flesh. Rodents possess incisors for chiselling through tough nuts and seeds. Feeding larger, unpeeled food items may give animals a chance to express these natural behaviours.

Nutrition Effects

Believe it or not, fruits and vegetables are still living when they reach your kitchen. Sitting there in the fruit bowl, each fruit is slowly respiring, its nutrient content changing. So, when you chop up the food, it triggers a series of chemical reactions that lead to nutrient breakdown.

Let’s look at this in more detail. First, and most obviously, a chopped fruit begins to desiccate: water molecules evaporate into the environment. This desiccation can be substantial, with some fruits losing more than 70% of their weight over a 12-hour period. For a species that rarely drinks, this could pose a challenge.

Nutritional changes also occur in the food. Vitamin C content, for example, rapidly drops in chopped food. Chopping also results in production of ethylene, a compound that speeds up food ripening. This leads to some foods becoming more acidic, and others becoming more alkaline. Complex carbohydrates like starches break down into simple sugars. Smaller food particle sizes, higher ambient temperatures and longer time periods since chopping result in greater nutrient changes. In a nutshell, food preparation actually alters nutrient content.

Other Considerations

With so many animals to feed first thing in the morning, you may well be tempted to chop up and mix all the food the afternoon before. That way, when you get to work in the morning you can feed your animals straight away. This sounds like an excellent way of prioritizing animal welfare, but it comes with its own challenges.

While nutritional breakdown slows down in cooler temperatures, it doesn’t stop. This means that the food, if prepared at 16:00 the day before, is already about 16 hours into its deterioration cycle by the time it is fed to the animals. This reduces the nutrient value of the foods being fed whilst also giving bacterial communities a chance to increase on the cut surfaces, and potentially reducing palatability. As a result, your animals may give this pre-prepared food the cold shoulder… if they have shoulders.

Going Forward

Back to your kitchen. The mound of fruit is still sitting there un-chopped, while your Head of Section fixes you with a glare that would make even a famous chef tremble. For today, you have a job to get through and animals / customers to feed. But it opens the question: what will the food prep kitchen of tomorrow look like?

For some species, it’s likely to be the same. Chopped food is useful for scatter feeds and enrichment devices. For some species, perhaps the chop could be smaller than before. For other species, perhaps the food will be delivered whole. Not only does this save you time, but it also means the food will stay more nutritious while giving your animals something to do.

Yet these changes won’t happen without evidence. Giving animals a choice of different sizes could allow you to identify preference – and checking food intake is important here too. By trialling different food presentation styles, we can build up a picture of what is best for the animals we care for. They won’t be awarding you any Michelin stars, but they will be benefitting from greater opportunities for natural behaviour!

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