Why is it that some horses with relatively straight hocks can exhibit great hock flexion at the trot? What might be the compensating factors in conformation that would allow that ability?
They exhibit more flexion because their hocks have a greater range of movement, due to the more open angle of the hocks.
However, a horse with straighter hocks is not always a better mover in the dressage sense – what is “good flexion” to a jumper is very different than to a dressage rider.
Open hocks (another word for straight hocks) seen in jumpers and some dressage horses, often means the horse’s hocks have a more open (or bigger) angle - good for jumping and folding limbs over fences. Those extra few degrees can make a big difference in stride, locomotion, and jumping.
This open hock is usually accompanied by a shorter, more angled femur as well – which will make the limb then have a steeper degree of articulation.
While good for jumping, it is not always good for long term soundness. Some horses in the top of the sport with this conformation really struggle to stay sound, but are brilliant athletes. Straighter hocks cause more stress on the stifles and suspensories, and also can impact the SI and pasterns.
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Beowulf, thank you–that’s very helpful.
The hock doesn’t exist by itself, so it’s really hard to point to the hock angle as a cause of more flexion. A given sickle-hocked horse (more closed angle than correct) might have more flexion than a straighter hocked horse, if that’s what his genetics dictates. For example, an ASB with sickle hocks is likely to have a lot more flexion than a horse bred for Hunters, and for sure a lot more flexion than a sickle horse bred for HUS or WP.
You have to look at the fibula (gaskin) length and angle to the femur, femur length and angle to the pelvis, and length and angle of the pelvis (short-hipped, long/deep, steep(er) croup or flat(er). And then the unseen genetics.
The straighter hocks can flex in a greater range of motion because of where they start (more open), but there’s nothing inherent about them that makes them flex more.
