To provide animals with the best welfare possible, we need to know what they’re feeling. Whether we’re talking about the companion animals that share our homes, animals in research laboratories or zoos, animals on farms, or even wildlife, having some reliable way to measure how stressed an animal is is crucial to understanding how best to respond and provide for their welfare needs. A quick look at the Faunalytics library shows that it’s a major topic, and one that we’ve covered quite extensively.

Measuring blood, salival, fecal, or urinary cortisol have all been used extensively as standards for measuring stress levels of different animals. However, those different measures “present only a retrospective timespan of a few minutes up to one or two days,” so understanding long-term stress becomes challenging. A newer approach has been to use hair cortisol, which can help in the evaluation of chronic or repeated stress. This is great news, because chronic stress “may cause higher biological costs of coping with the stressor, diverting resources away from other biological functions such as immune competence, reproduction or growth.”

In this review researchers gathered together available research to assess the applicability of hair cortisol tests to measure chronic stress in both wild and domesticated animals, and is the first review that “outlines the various fields of application of hair cortisol analysis focused on animal species.” Though many of the studies they review look at companion animals, they also look at farmed animals, zoo animals, wildlife and beyond.

The review finds that, for companion animals, solitary housing of dogs decreased hair cortisol concentrations (HCCs) compared with dogs in multi-dog households, but increased HCC compared with paired housing. Meanwhile, there was a positive correlation between HCC and the length of time dogs were regularly left alone, indicating a higher stress level caused by solitary housing. The review also found that competition dogs had higher HCC than companion and professional working dogs.

Of course, the review is not without some caveats. Through their analysis, the authors find there are certain “best practices” that can help to make measurements more accurate and reliable. Among them, using samples from animals of the same group, sex, and age, as well as sampling hairs from the same body region and color is preferable. As with other methods of stress measurement, researchers should also do their best to avoid contamination and be mindful of the time delay between cortisol incorporation and the sampling of hair.

For companion animal (and other) advocates, the study shows that using hair cortisol is a promising and powerful tool that “offers many considerable benefits for use in animals, especially due to the easy and minimally invasive sampling procedure and the representation of longer time periods in one sample.” Though most advocates likely won’t have the tools at their disposal to make these measurements themselves, their knowledge of the procedure may help them to advocate for its use where necessary. Finally, since the study is, as of press time, an open access article, animal advocates can peruse the findings themselves, which give quite a comprehensive picture of some of the ways that hair cortisol has been used to assess stress in companion animals, farmed animals, wildlife, and more.