Question:

Why does my usually well-behaved horse suddenly buck or rear for apparently no reason?

Answer:  (A great answer from Temple Grandin, Colorado State University)

This may be caused by an old fear memory being triggered. Often the problem occurs when the horse transitions from one gait to another. When the horse was first trained, too many new things may have been forced onto the horse too quickly. This may have caused him to get very frightened. This is especially a problem in more hot-blooded horses. Memories in animals are sensory based and they would be stored in the brain like pictures, audiotapes or specific tactile touch feelings. When a horse changes gait, a saddle feels different. The weird feeling of cantering with the saddle for the first time may have frightened the horse. A horse with a calm disposition can be more quickly introduced to new things than an animal with a flighty, excitable disposition. Fear memories are very specific. I observed a horse that was afraid of black cowboy hats and white hats had no effect. The horse’s fear was due to being abused by a man wearing a black cowboy hat. If the object the horse fears can be removed, bucking and rearing my stop. It may also be possible to calm the horse down by talking to him. I have observed that a horse or cow will often calm down when it hears the voice of a person it trusts. The bucking problem that occurs when the horse changes gaits can sometimes be prevented by substituting a completely different saddle or pad that will feel different. Tack that feels different may not trigger the old fear memory. If a horse has been abused with a bit, try a hackamore. A bit with a completely different design may also work. The worst thing a person can do is to punish fear-based behavior. Punishing fear just makes it worse.