Historically veterinarians have used blood tests to check a horse's stress levels. While the most common test is measurement of the cortisol level in the blood, a saliva sample may also be used, as salivary cortisol levels have been shown to be an index of blood cortisol levels.
An elevated cortisol level requires additional testing to determine if the cause is related to a physical problem, hormone imbalance, or to stress or other factors.
In March, Belgium scientists announced that using a saliva assay (test) is as reliable as a blood test. Because of the ease in testing, authorities are saying that the saliva test may well become the test of choice for testing stress in horses.