Examining Form to Function
Hind-end conformation can affect horse health and performance.
December 11, 2013
From The American Quarter Horse Journal.
When a horse’s bone structure differs from the ideal, it’s called a structural deviation. Although a conformation fault is not inherently problematic, it can cause major issues if unsoundness, lameness or other health concerns develop as a result.
Jim Heird is the Executive Professor and Coordinator at Texas A&M University’s Equine Program. He along with Don Topliff, Ph.D., and AQHA Professional Horseman Jeffrey Pait, are responsible for instructing fellow AQHA judges on conformation evaluation. Here they explain the common structural deviations in hind limbs.
“We sometimes forget that so much of what we ask our Quarter Horses to do are athletic maneuvers that require a horse to be supple in the hindquarters and hock and be able to work under themselves,” Jim says.
“Because the horse carries 60 percent of his weight on his front end, there is not as much concussive force on the hind end as there is on the front.
“But what you do have is more stress on the joints as the horse sits or turns, as with a reining or a cutting horse. The strain in the hock, fetlock and stifle are tremendous as the horse applies torque and tension on those joints.”
Remember, very few horses meet the ideal in every way. Some deviations are more acceptable than others.
Sometimes a slight deviation might improve performance in a particular event, but too much deviation increases the likelihood of lameness.
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“You want to try to assess if a deviation is severe enough that it could cause a soundness problem down the road,” Don says.
“Being structurally incorrect does not guarantee a horse won’t be sound,” he adds. “But the vast majority of unsound horses are structurally incorrect.”
From The Rear
Imagine a vertical line dropping from the point of the buttocks (or pin bone) to the ground. In the ideal hind limb (seen from the rear) the line should go down through the center of the hock, cannon bone, fetlock and pastern and into the ground.
“You want the forces of concussion and strain on the joint to be evenly distributed across the hock,” Don says.
“If a horse is not straight through the hock, and its lower limb is not aligned with the upper limb, then the line of force through the hock will change direction. That focuses the strain on one side of the joint. That’s a predisposition to unsoundness.”
A horse that is “in at the hocks and out at the ground,” or “cow-hocked,” is the most common hind limb deviations, Don says.
In the cow-hocked horse, as the ideal line drops down, more of the hock joint will lie to the inside of the line.
“In that horse, the concussion is focused on the inside of the joint,” Don says. “Depending on how much he is cow-hocked, the horse will potentially get sore in their hocks or end up with a bony change in the hock that might create unsoundness.”
In a bowlegged horse, more of the hock joint lies to the outside of the ideal line. The strain on the hock is focused on the outside of the joint.
“They will move wide behind,” Don says. “They swing wide and then back to the center. It takes the leg away from the center line of the horse, so he loses power.”
From The Side
Imagine a vertical line dropping down from the point of the buttocks (or pin bone) down to the ground. In the ideal hind limb (seen from the side) it should touch the point of the hock, run along the back of the cannon bone, touch the back of the fetlock and then to the ground.
The cannon bone is parallel to the ideal line and perpendicular to the ground. To see many hind limb deviations from the side, look for how the ideal line relates to the position of the cannon bone.
“In a sickle-hocked horse, the cannon bone will slant forward of the ideal line and won’t be parallel to it,” Don says.
There is too much angle to the hock, putting undue strain on the ligaments along the back of the joint.
“Any time you have a horse that’s excessively sickle-hocked, that’s a predisposition to unsoundness,” Don says. “We see a lot of curbs in those horses.”
If a horse is camped-out behind, the cannon bone is perpendicular to the ground; but, as the ideal line comes down it runs in front of the back of the hock and cannon bone.
“Some horses stand naturally with their cannons and hocks far back behind them,” Don says. Those horses are truly camped-out behind.
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“If you take the sickle-hocked horse and stretch him out to where his cannon bone is perpendicular to the ground, the hocks will be back behind him,” he says. “It’s just a matter of how he’s standing.”
A post-legged horse can be deceiving. The ideal line might follow down the leg properly, but there is too little angle in the hock and stifle. The hind limb can also be so straight that, as the ideal line drops down from the point of the buttocks, the hock and cannon bone are in front of the line.
“The post-legged horse is the hardest to see,” Don says. “You can drop that ideal line down, and it’ll look like it goes in the right place. But that doesn’t mean there’s not a problem in the stifle joint because the angle is excessively straight.”
The straighter those angles, the less ability the horse has to flex and move off its hocks.
“We look at the hock and say they’re straight in the hock, but it starts in the next angle up. The horse is actually too straight in the stifle joint between the femur and the tibia and fibula,” he says.
“It’s similar to the horse that’s straight in the shoulder. The hock has lost the ability to absorb concussion, and the horse will be short-strided.
“I’d say we’ve not been hard enough on post-legged horses,” Don says. “But I think we’ve come a long way toward getting some angle back in the hock, particularly in the halter horses.
“In performance horses, it’s the other way around. We have not been hard enough on sickle-hocked horses.”