Stress Levels Measured in Horses’ Saliva

Cortisol, a known indicator of stress, is usually measured by taking a sample of a horse’s blood and determining the amount of cortisol present. Obtaining a blood sample is invasive, somewhat painful for the horse, and difficult to accomplish if the horse is nervous and won’t stand still for the procedure. Scientists in Belgium theorized that measuring cortisol in a horse’s saliva might allow a comparably accurate figure. Produced in the adrenal glands and secreted into the bloodstream when a horse is exposed to stress, cortisol diffuses into the salivary glands, but it was not known whether levels detected in saliva would correspond to levels found in blood. In the experiment, researchers administered ACTH to horses to trigger the release of cortisol. They collected blood by intravenous catheter and saliva by using a cotton swab. When cortisol analysis was performed by radioimmunoassay, levels in blood and saliva were strongly correlated. Collection of saliva, being quick and painless, might be a preferred method of taking a sample for cortisol analysis while offering the same accuracy as a blood sample.