I get a lot of horse training questions about stopping a horse from kicking. The kicking habits of these horses range from horse kicking at virtually anyone to kicking at only husbands. It's a daunting problem that lots of people have no idea how to cure. That being so, I want to share some insight to horses kicking.
First I want to relate some causes of horses starting in habit of kicking. Because a horse kicks is no reason to think he is naturally bad or unmanageable. I don't think there is a horse alive that is "naturally" vicious. In fact, they're made that way due to bad management or ignorant handlers.
Admittedly, there are some horses that inherit characteristics of their ancestors. But one should never start to break a horse without first taking into consideration nature, disposition, and understanding of a horse.
For instance, there are some horses that are naturally predisposed to have a "not so good" disposition. There are certain physical characteristics you can spot on a horse that indicate what his disposition is like.
Jesse Beery, a famous horse trainer from 1800's, was brilliant at deciphering a horse's disposition. He even wrote extensively about how to do it. You can read about it at http://www.horsetrainingandtips.com/Jesse_Beery_etips.htm.
Anyway, now we can handle horse according to its disposition. We can get it very nearly equal with a good dispositioned horse. All difference in world is due to management and training of colt. A horse with a "not so good' disposition will require more patience and thorough work.
All animals in nature have a self defense of some sort. A horse's self defense is kicking. After all, if you work with a horse that gets badly excited by some cause (such as ropes or chains coming in contact with his legs and those parts of his body aren't broken) his first inclination is to kick it out of way.