The first part of any lameness exam is figuring out which leg is lame. This sounds obvious, but it is this first step that seems to throw so many people, even very experienced riders.
Let’s say that your horse goes lame because he stepped on a nail. There will be no question which leg hurts. The horse will bear almost no weight on the leg while standing. When an animal has an early arthritis, it’s not so easy. At first there might be some reluctance to work. Eventually it will become more and more apparent that he is a little off. He might stand solidly on all four and be sound at a walk, but trotting he will show a lameness. It is at this point that people get confused as to which leg is the sore one.
If this has happened to you, you aren’t alone. More often than not, when I am asked to look at a lame horse, the owner has pin pointed the wrong leg. At the beginning of our equine lameness course in vet school we were shown films of 10 lame horses and were asked to write down the off leg in each film. I got 5 wrong. Actually, as I didn’t have a system I think my correct answers were all guesses. If you don’t have a system for evaluating lame horses, it is mostly guess work. All you know is that that you see a blur of four moving legs and that the horse isn’t moving correctly.
To be sure that I could explain the system I put a small stone in the heel of my right shoe so that when I walked it would hurt. Then I asked my wife, Bonnie, who has no real horse experience, to tell me which leg was being favored as I walked. She could only tell that I was limping, but didn’t know which leg. Then I asked the key question: “When I walk, which foot is hitting the ground harder?” She could see that. In fact she could hear it I shifted the stone to the other foot and asked the question again. Again, she was able to tell. I explained that if one leg is taking most of the weight, then the other one is taking less, and is the sore one. She got that, and then was able to tell which leg was sore. Try this with a friend. Again, the foot that doesn’t hurt will hit the ground hardest. The good leg takes the shock. So, if the right one is coming down harder then the left one is the sore one.
Believe it or not, that’s all there is to it. If you get that concept, you are ready for lame horses. It’s actually easier on horses because the head and neck of a horse weigh so much, and horses use this in favoring the lame leg. When a sound horse trots, the head stays on an even line. When he is sore the head comes down when the good leg hits the ground and goes up when the lame leg hits the ground. In other words, the good leg is taking the weight of the head and neck. Watch for the head coming down. When it does, you know that the sound leg is hitting the ground, and the other leg is the sore one. This is called a head nod.
Don’t let the fact that a horse has four legs confuse you. When you watch a horse go, first watch only the front end. If one of those feet is hitting the ground harder (the head nod), the horse is lame up front. Now watch the hind end. If one of those two feet is hitting the ground harder, you have a hind end lameness. For sure, there are refinements that come with time and experience, but if you start with these basics, and always ask which leg is taking the weight, most of the time you will know that the opposite leg is the sore one.
–David A. Jefferson, DVM