Immediately. Once your horse learns to buck and if it is effective at him getting his way, he may develop it as a strategy for showing his displeasure at being ridden or controlled. An isolated incident with no clear reason for bucking is nothing to worry about, but your horse may develop into a problem animal if bucking produces a desired response from you, his rider. If he doesn’t have to carry you after he bucks, he learns to buck when you want to ride him.
A horse can be reacting to negative reinforcement from his owner or trainer and bucks. He might be associating riding with pain or discomfort and use bucking to show his fear of it, long after the pain has subsided. Once your horse has used bucking to avoid being ridden, it could become a learned behavior that you must stop. Thinking about ways to solve this problem in a positive manner will go a long way toward stopping the bucking and strengthening your relationship with your horse.
The BuckBuster anti-buck bridle was built for just this purpose. To quickly stop the behavior by teaching the horse through positive reinforcement. Once a horse lowers his head to prepare to buck, the halter puts pressure on him, which is uncomfortable – but not harmful. When his head is up, he/she is immediately rewarded by the halter loosening the pressure. This is the time to praise him for not bucking. When his head is up and it can’t be done.