Saliva vs. Blood for Measuring Equine Stress Levels

What do a horse's stress level and his saliva have in common? Belgian scientists have found testing the former can measure the latter, and they said this saliva assay could become the test of choice for measuring horses' stress.

"Cortisol levels are often measured in horses to assess stress induced by transport, competition, training, and stereotypies," explained Marie Peeters, MSc, a PhD candidate at the Faculty of Veterinary Medicine in Liege, Belgium. Measuring equine stress levels is also an important part of some equine welfare studies.

Previous research revealed that cortisol, also called "the stress hormone," is released from the adrenal glands near the kidneys into the bloodstream. The hormone then diffuses into the salivary glands; therefore, Peeters and her colleagues suspected they could obtain constant, measurable information regarding cortisol levels in the blood by testing saliva.

To determine whether salivary cortisol levels were comparable to blood cortisol levels, the team collected samples of both body fluid types from five horses before and after stimulating the release of cortisol with a drug called adrenocorticotrophic hormone (ACTH).

Researchers collected blood samples using an intravenous catheter, whereas they collected saliva samples with cotton swabs.

The researchers noted a strong correlation between blood and salivary cortisol levels and that the test kit (a radioimmunoassay) reliably measured cortisol levels in both fluids.

So, why saliva? Pulling blood for evaluation is invasive and sometimes difficult to achieve with a nervous or fractious horse, not to mention more costly.

"In contrast, saliva-sampling is a noninvasive, painless, and stress-free method of measuring cortisol levels in horses," noted Peeters.

She concluded, "Measuring salivary cortisol concentrations is a more welfare-friendly method than blood sampling, and only the free, or biologically active, fraction of cortisol is measured. This will be a good method of measuring stress in horses in future studies instead of measuring blood cortisol levels."

The study, "Comparison between blood serum and salivary cortisol concentrations in horses using an adrenocorticotrophic hormone challenge," is scheduled to be published in an upcoming edition of the Equine Veterinary Journal. The abstract is currently available online.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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