Horses communicate primarily through body language. They don't have hands, thumbs or the ability to talk, so a simple gesture can be interpreted in a variety of ways. A horse can stomp his foot for a number of reasons, and it might or might not mean anything of any real importance.
Horses can't use hands to brush flies and other bugs away from their skin. It is completely normal for a horse to stomp his hoof to shake flies off his leg. He also removes flies by swishing his tail against his legs and rubbing his legs with his face. Fly-related stomping can often be significantly reduced by spraying your horse with a good quality fly spray.
Your horse might have learned that stomping is a good way to get your attention. For example, if you go to him and check on him every time he stomps his foot to remove flies, he'll learn that a stomp is a good way to call the human over. Pawing is a slight variation of stomping in which the horse uses one front leg to perform a repetitive digging motion on the ground in front of him. It is considered a vice.
A horse might stomp when he's impatient. This behavior is often seen when a horse has been tied up for a long period of time, or around feeding time. Repeated stomping can quickly turn into pawing, and the horse normally does it to catch your attention and express his impatience. The horse might think that to get him to stop, you'll hurry up and do what he wants.
Horses have been known to stomp or trample small predators such as snakes. They sometimes stomp at one another while trying to establish dominance in the pasture. Your horse could stomp just because something, such as tall grass, is tickling his leg. Stomping combined with other symptoms such as rolling or belly biting can be a sign of discomfort or pain caused by colic. Sometimes horses stomp just because they feel like it, or for reasons that aren't evident or obvious to people.
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