Skeletal Maturation

“What we know about the rate of skeletal maturity is that the growth plates in the equine body slowly fuse between one-and-a-half and six years—across the board. There is no truth to the myth that some breeds of horses mature faster than others. All horses reach skeletal maturity at about five-and-a-half to six years of age. This really shouldn’t surprise us as we know that horses continue to erupt molars until they are five. Why shouldn’t the timing for completion of growth be at about the same?

What may not be common knowledge is that it’s not the legs that are the slowest maturing part of the body. The growth plates of the knees mature (or close) at about two years for the small bones and three years for the distal radius and ulna. The very last growth plates to fuse are in the equine vertebrae. All 32 of them! The last of those are the ones in the base of the neck.
The reason this is relevant to our young horses that we plan to ride well into their advanced years is that the process of riding our young horses can contribute to not only excessive wear and tear on their young joints (the hocks also don’t fuse until three-and-a-half years) but strain to their back and neck as well (fig. 1).

The process of teaching a horse to be ridden at a very young age teaches the horse to protect himself from back pain. To do this, the horse braces his back and drops his shoulders and hollows out so that he can help take the weight off his vertebral column. It’s a minor thing at first and one that every young horse being started under saddle goes through to a certain degree until his back muscles get better 
at carrying weight. But if you persist in riding a young horse whose vertebral column is not able to bear that weight—even with muscular conditioning—you create a habit caused by pain that becomes deeply ingrained and prevents the horse from properly learning to round up and use his body.

The next step in training a young horse after getting on his back (especially in many of today’s “natural horsemanship” methods) is the one-rein stop. This is accomplished by repetitively pulling the horse’s head over to your foot and limbering up the neck until it is quite soft and “rubbery.” Isn’t this putting added stresses on the last vertebrae to fuse in the horse’s entire body?

Pain here causes stiffness in the bridle that makes the horse flex by turning his head at the atlas rather than flexing his entire vertebral column. With vertical flexion, he then learns to brace his withers, and instead of flexing along his entire column, will flex at the third vertebra to protect the rest of the cervical vertebrae. All of this might look like a broke young horse to the uninitiated, but in truth it is a horse with reflexes built on pain. These horses can never move in a true collected frame.

Does this mean that we shouldn’t start our horses until they are fully skeletally mature? This, for me, is a hard question to answer.
Paired with the data of skeletal maturity is the data that exists on mental maturity. Horses can and do learn to learn. One of the great things that have been bred into the Quarter Horse performance horses is their ability to calmly and easily learn what is expected of them. They are almost “born broke.” This is because they have been selected for train-ability, which is really the capacity to learn. (Whether this makes them the smartest breed of horse or just the most train able is a discussion for another time!) For most folks that work with young horses and start colts, the ones that have had an introduction to good handling and training as yearlings are much easier to start as two- or three-year-olds. This ability to retain a lesson and understand what is being taught is a learned behavior. The younger they learn this, the easier they seem to be to train and quicker they come to trust human handlers.
Therefore, I believe the answer lies in moderation, as with most things. I think you must take into consideration your youngster and your training program. I am 100 percent not in favor of futurities that demand a horse be put into rigorous training as a two-year-old. I am also not in favor of any practice that deems it common and prudent to inject a young horse’s joints to maintain joint health or cover up lameness and keep him working. But, that’s just me. I have many colleagues happily performing these procedures and building their retirement accounts much faster than I am.

I don’t think you necessarily need to completely stay off your horse until he is four. I think you can teach a young horse some valuable lessons, expose him to important stimuli and situations, and in general, build his confidence and ability to learn as a young horse.

I don’t feel that lack of skeletal maturity means no work or riding at all, but I think it means conscientious riding and training to preserve not only your horse’s mind but his physical ability to be able to be 
a good sound partner throughout his entire life. I want to be riding my horses well into their second decade and possibly longer. There
 is nothing sadder to me than a six-year-old that is too lame to be ridden in the show pen anymore because he was ridden too hard as a youngster.  Too much work too soon. We need to be smarter than this for our horses. Increasing the usable upper-age limits of our horses through smart training will go miles to decreasing the numbers of unwanted or crippled horses out there”.

Jenni Grimmett DVM
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