When animals are kept in farms and zoos, some species deal with it better than others. New research finds that the type of food they receive and how they mate have an impact on how stressed they are.

“There are over 5 billion hoofed animals (known as ungulates) kept in captivity around the world, yet we know relatively little about why some of these animals cope well in captivity while others become stressed,” study co-author Leanne Proops from the University of Portsmouth in the U.K. tells Treehugger. “Given the vast numbers of ungulates under human care, we believed it was imperative that we understand more about what impacts their welfare.”

In the past, she says, research often just studied one species at a time, so many were not studied at all. This time around, they wanted to analyze risk factors for stress in all hoofed animals. The goal is to understand stress risk factors across all species and to predict which animals were most likely to be stressed.

“Ultimately, our research can be used to improve the welfare of all ungulate species, not just those lucky enough to have been studied individually,” she says.

Food and Mating

For their study, researchers collected data on 15,236 animals across 38 ungulate species from 95 sources such as farms, zoos, and safari parks. They measured stress by observing rePuppyitive behaviors that are often seen in captive animals. Known as “stereotypic” behaviors, these can include pacing, bobbing, and oral movements like licking walls or biting enclosures.

Researchers also took note of the size of each animal’s enclosure and how often they were fed with what type of food. They measured each species’ natural behavior such as the distance they travel every day and their mating behaviors. They used statistical models to determine how much of an impact each of these things had on whether an animal showed stress-related behaviors.

They found that species such as camels and okapis, which naturally feed on trees and other high, woody vegetation, are more likely to exhibit stress signs over those that mostly eat grass.

“Animals who do not have constant access to feed, and are fed relatively little plant material in captivity, are also at higher risk of becoming stressed,” says Proops.

In addition to these “browser” species, they found that “promiscuous” animals are more likely to be stressed in captivity. These are animals like African buffalos, sheep, and pigs where males and females mate randomly with each other.

The findings were published in the journal Proceedings of the Royal Society B.

Lowering Stress and Improving Welfare

Interestingly, researchers point out that their results were considerably different from studies that examined primates, carnivores, and parrots.

“This tells us that the causes of stress differ from one group of animals to another, and that we therefore need to be tailoring our care of each group to their specific needs,” co-author Kate Lewis, from the University of Portsmouth, tells Treehugger.

The findings also show that social, mating behaviors can have an impact on stress.

“Mating has historically been overlooked when considering an animal’s welfare. Here we have shown that this should not be the case, and that we need to change our approach,” Lewis says. “We hope that our results will spur greater consideration of the mating needs of animals kept in captivity.”

Researchers hope that their results will be used to lower stress and improve welfare for captive, hoofed animals. Caretakers can do that by offering feeding toys that encourage browsing animals to eat the same way they do in the wild. The study also recommends having constant access to food, especially plants.

“We hope that the risk factors for stress highlighted in our study will be used to inform the design and development of enclosures, enrichment items, and breeding programmes for ungulates in the future,” says Lewis.

“Because of the approach we used, our results can be used to predict the likelihood of a particular animal or species becoming stressed, even when there is no tailored information available for that specific species. This will allow animal keepers to make informed decisions about that animal’s suitability for captivity, and to ensure that housing and husbandry for these animals promotes good welfare from the outset.”