To use a pair of hoof testers, Chris Gregory first watches the horse go, so he can determine which foot he thinks is lame. Once he's done that, he picks up the sound foot.
"Going over the sound foot with the hoof testers first is a good way to determine if the horse will react to any pressure from the hoof testers, or only when the pressure is in the right (wrong) spot," says the owner of the Heartland Horseshoeing School in Lamar, Mo.
"Some horses are very stoic and won’t react visibly to pain, even when they are sore. Others are jut the opposite and will act badly throughout the testing process. Determining the reaction of the horse on the sound foot helps me discover what type of horse I’m dealing with."
Bear in mind that this is a living animal you are working on. If you were to put one of your fingers in a pair of pliers, you could squeeze softly enough that your finger wouldn’t hurt, or hard enough to cause pain for your perfectly sound finger. You can do the same thing to a horse with hoof testers.
Gregory's advice: Begin on one heel. Squeeze lightly, perhaps with enough force to wring out a wet sponge, then move forward about an inch and squeeze again. Continue around the foot, advancing 1 inch at a time, until you reach the opposite heel.
From that point, squeeze with one jaw at one side of the frog, and the other on the opposite side at the widest part of the foot. Do the same to the opposite side of the foot and frog. You can also squeeze across the heels.
Each of these positions is designed to elicit a response of pain from an injured foot. On the sound foot, there shouldn’t be any response in the normal horse. So, when the horse does react, you know that you have hit a sore spot on the foot you’re actually testing.