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)