Had an osteology lecture this morning that included (among a plethora of other things) a radiograph (xray) of a young dog that had a injury to his *radial distal physis that caused the distal growth plate to close early.....while the ulna growth plates continued to remain open and elongate the ulna normally.
So, the ulna is continuing to grow and elongate.....and the radius doesn't.
What do you think happened?
It did awful things to the elbow joint. The ulna was growing longer and pushing the elbow joint away from the radius/elbow connection and gaps where forming in the elbow joint where there should be no gaps! It was obviously deformed, looked painful, and it was not hard to imagine the loss of function in this young dog.
As horse people (and dog people) we hear about growth plates all the time. I guess I had some vague notion that asking too much from a young animal could result in arthritis and other problems "down the road". I didn't realize the SIGNIFICANT and IMMEDIATE impact that damage to the growth plates can have on your young dog/puppy right now. There's definitely degrees of injury, growth plate closure isn't always the result, and it isn't always catastrophic....but my point is, if you damage that growth plate by overworking your young horse or dog - it isn't someone else's problem down the road, or that the animal will be more "creaky" upon retirement, or shorten their performance career by a bit - you could be killing that career before it even starts.
Seeing is believing. I'm not able to post slides from school because of copywrite limitations, however, here's an image from University of Pennisylvania's website that I found through google - in this case the bones are bending, and not necessarily destroying the elbow joint like the example I saw in lecture - but you get the idea.
For the horse people - Don't give your young horses a job that has a chance of damaging the growth plates. How to define young? Have a frank conversation with your vet. Do a lot of personal research. When in doubt, wait a year. Being damn sure those plates have closed before starting work will more than repay the year you loss, in the years you will gain during their career.
For the dog people - even in a medium sized dog the plates may not close until 18 months or so. The "1 year" designation is completely arbitrary. If you are planning on doing agility, it is especially tempting to start jumping them too early - and you may think that if you have a medium sized dog you are safe to do so at a year or even a bit earlier. You will be better served observing what the large-breed people do, and waiting. There are plenty of ways to teach jumping problem solving without jumping height. It doesn't matter how "mature" you think your dog is - there is no harm in waiting. Work on your handling skills and jump bumps and problem solving skills - your dog will naturally transition to full-height jumps easily if you've laid the ground work. And, just like in the horses, waiting will pay time dividends that will more than pay for waiting that extra 6-7 months.
* These are your vet terms of the day. The radius is the weight bearing bone in the forearm, the physis is the growth plate, distal meaning the growth plate at the end of the radius closest to the paw. The ulna is that second bone of the forearm that runs parellel to the radius - it's a skinnier bone that provides support (and "other stuff" I haven't learned yet, I'm sure)