One example which speaks louder than any words is that of the extremely highly-regarded dressage rider, Reiner Klimke. This talented German rider consistently produces well-adjusted horses with outstanding balance and exceptional performance. Yet he says in his book, Basic Training of the Young Horse, "I believe that the experienced trainer of riding horses will not start work with his charge until the growth of the joints, bones and tendons is well advanced". His training programme includes riding only at the end of the third year, and sometimes not until the horse is four. His excellent results do not seem to suffer from giving his horses a late start: indeed, he says, "I am convinced that had I started these horses earlier I would not have been so successful."
Perhaps we can learn from the gentle pace of this expert approach. As Klimke says, "One must have the patience to wait until the horse is physically and mentally ready for the work demanded of it."
More articles about the training of young horses:
Thank you to http://horseracing.about.com/sports/horseracing/ for the horseracing photo