Continuation of an article by ©2005 By Deb Bennett, Ph.D.:
What Does it Mean to “Start” a Young Horse?
Let us now turn to the second discussion, which is what I mean by “starting” and the whole history of that. Many people today – at least in our privileged country – do not realize how hard you can actually work a mature horse – which is very, very hard. But before you can do that without significantly damaging the animal, you have to wait for him to mature, which means – waiting until he is four to six years old before asking him to carry you on his back.
What bad will happen if you put him to work as a riding horse before that? Two important things – and probably not what you’re thinking of. What is very unlikely to happen is that you’ll damage the growth plates in his legs. At the worst, there may be some crushing of the cartilages, but the number of cases of deformed limbs due to early use is tiny. The cutting-horse futurity people, who are big into riding horses as young as a year and a half, will tell you this and they are quite correct. Want to damage legs? There’s a much better way – just overfeed your livestock (you ought to be able to see a young horse’s ribs – not skeletal, but see ‘em – until he’s two).
Structural damage to the horse’s back from early riding is somewhat easier to produce than structural damage to his legs. There are some bloodlines (in Standardbreds, Arabians, and American Saddlebreds) that are known to inherit weak deep intervertebral ligament sheathing; these animals are especially prone to the early, sudden onset of “saddle back’” However, individuals belonging to these bloodlines are by no means the only ones who may have their back “slip” and that’s because, as mentioned above, the stress of weight bearing on the back passes parallel to its growth plates as well as parallel to the intervertebral joints. However, despite the fact that I have provided a photo of one such case for this posting, I want to add that the frequency of slipped backs in horses under 6 years old is also very low.
©2005 By Deb Bennett, Ph.D.
TIMING AND RATE OF SKELETAL MATURATION IN HORSES,
All Horses of All Breeds Mature Skeletally at the Same Rate
There is no such thing as an ‘early maturing’ or ‘slow maturing’ breed of horse. Let me repeat that: no horse on earth, of any breed, at any time, is or has ever been mature before the age of six (plus or minus six months). So, for example, the Quarter Horse is not an “early maturing” breed – and neither is the Arabian a “slow maturing” breed. As far as their skeletons go, they are the same. This information comes, I know, as a shock to many people who think starting their colt or filly under saddle at age two is what they ought to be doing. This begs discussion of (1) what I mean by “mature” and (2) what I mean by “starting”.
When is a Horse Skeletally Mature?
Just about everybody has heard of the horse’s “growth plates”, and commonly when I ask them, people tell me that the “growth plates” are somewhere around the horse’s knees (actually the ones people mean are located at the bottom of the radius-ulna bone just above the knee). This is what gives rise to the saying that, before riding the horse, it’s best to wait “until his knees close” (i.e., until the growth plates convert from cartilage to bone, fusing the epiphysis or bone-end to the diaphysis or bone-shaft). What people often don’t realize is that there is a “growth plate” on either end of every bone behind the skull, and in the case of some bones (like the pelvis, which has many “corners”) there are multiple growth plates.
So do you then have to wait until all these growth plates convert to bone? No. But the longer you wait, the safer you’ll be. Owners and trainers need to realize there’s a definite, easy-to-remember schedule of fusion – and then make their decision as to when to ride the horse based on that rather than on the external appearance of the horse. For there are some breeds of horse – the Quarter Horse is the premier among these – which have been bred in such a manner as to look mature long before they actually are mature. This puts these horses in jeopardy from people who are either ignorant of the closure schedule, or more interested in their own schedule (for futurities or other competition) than they are in the welfare of the animal.
It’s a little hard to see, but this diagram shows how the skeleton of a horse matures.