Capillary refill time (CRT) is a quick and easy test that provides a rough assessment of a horse’s blood pressure and circulatory health. Normally it takes 1-2 seconds for blood flow to return to the gums after they are blanched by pressure with a thumb.
If it takes longer than this, a horse may be suffering from low blood pressure due to shock, dehydration, poor heart function or other problems.
Halter your horse and move it to an area with good consistent light. Stand on the left side of the horse. Wear latex gloves. Place your left hand index, middle, and ring fingers on top of the horse's muzzle, using feel to keep contact with your horse.
Use your thumb to lift the lip. Use your right thumb to apply pressure to the gums (blanching), just above an upper incisor tooth. This causes blood to temporarily leave the area, and the gums turn white. Now count the number of seconds for the color to return to pink. This is the CRT. Repeat this several times and average between them for the time.
Tips for safety & Success
Ensure that lighting is consistent. Check both left and right sides of the upper gums because you may notice a significant difference between them. Ensure that nothing else is compressing the membranes you are examining, because this will interfere with blood flow and affect your findings.
Be careful not to put excessive pressure on your horse's muzzle or block their nostrils while performing this skill. This will cause them to resist.
There is a rare but potentially fatal possibility for you to contract rabies from a horse infected with this disease if their saliva comes into contact with a wound on your skin. Due to this, it is recommended that you ALWAYS wear latex gloves when examining your horse's mouth.