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Tuesday, 01 March 2011 16:28

“DOC – WHAT IS THE DIFFERENCE BETWEEN A ‘CURB’ ON A HORSE AND A ‘CURBY HORSE?’

Written by  A.J. Neumann, DVM
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That’s a very simple question which is often asked of me when I am teaching about problems that can arise in the hock of the horse. It is very easy to illustrate a curb or a curby hock on the live horse but it becomes a problem to set it all down in writing. With some misgivings, I’ll give it a try.

First of all, we have to know where the hock is located on the horse. You would be surprised how many people call me about a lame horse and I find in talking with them they do not know what the hock is. Suffice it to say that the hock is located on the rear leg of the horse. It is that structure with the point of bone on it about halfway up the rear leg of the animal.

The hock is made up of a number of bones and is known as the “tarsus.” The tarsus, for practical purposes, rests on the metatarsus, or the long lower leg bone which ends at the fetlock or ankle. This joint is therefore known as the “tarsal-metatarsal joint.” I find that a lot of pathology can occur in the area of this joint. It is interesting to note that cattle, deer, elk, sheep, pigs and a host of other animals have the same anatomic makeup in their rear legs as that of the horse.

Anyone who has hunted or butchered these animals is aware that the lower rear leg can easily be severed with just a knife at this joint. The rear quarters, or the whole carcass, can then be suspended by the hocks just as the butcher does with the hind quarters of beef.

The large tendon at the rear of the lower leg passes over the tarsal-metatarsal joint. There is also a ligament in this exact area named the “plantar ligament” which, along with other ligaments, aids in tying this joint together.

The curb, when found on the horse, occurs in the area of the joint on the very rear of the leg. It is an inflammation of the plantar ligament which causes an enlargement of the posterior surfaces of the limb exactly over the tarsal-metatarsal joint.

A curb can occur in the normal, formed hock, but is much more prevalent in the sickle hocks or “tied in” hocks often known as a “cow hocks.” These hocks become quite susceptible to strain of the plantar ligament when the horse is jumping or engaged in heavy pulling. Any severe strain on these hocks may cause the formation of a curb.

A curb can only be seen clearly from the side of the leg. It will be a prominent swelling at the junction of the tarsal and metatarsal bones. The swelling will decrease in size above and below this point. If the curb has developed suddenly, there will be a lot of inflammation present and the animal can be severely lame.

When the horse with a curb is resting, the foot is held with the heel off the ground and when walking the weight is born on the toe.

If the stricken horse has hocks of good conformation, the condition can be easily treated. However, in those cases with hocks of poor conformation, the curb may not respond to therapy and lameness may be chronically present.

The curb is always an unsoundness as well as a blemish!

Now that I have described to you the condition known as a “curb,” let us have a look at the “curby” horse.

A very good hock should be long, clean and flat. What does this mean?

The whole hock structure should be relatively long and not short and thick. It should be clean. This word “clean” when applied to the hock, means the structure should be hair, skin and bone. There should be no evidence of fluid under the skin or tissues of any kind other than bone. The ideal hock is not “filled” with fluid or “meaty” to the touch.

Horsemen use the term “flat” to describe the hock which is smooth on the inside and outside. It is free of “bony knots” and bone projections. If a hock has the latter aspects it is often known as a “rough hock.”

The very good hock, then, will be long, clean and flat; not filled, meaty or coarse or short. It will not be sickle-shaped, “camped” in or “bowed out.”

If you run your hands down the inside and outside surfaces of the horse’s hock you will reach a point where your fingers have left the tarsal bones and have reached the metatarsal bone. At that point the tips of your fingers are exactly on the tarsal-metatarsal joint, which we previously described in writing about the curb.
Any old farmer, hunter or butcher knows this trick, as it is one way to determine the location of the tarsal-metatarsal joint. This joint must be opened to sever the lower leg from the rest of the carcass.

As the hand descends on the outside of the hock the fingers slide down on what feels like a ridge of bone. When one reaches the end of this ridge, the fingers should be on the joint and they should be 1 to 1-½ inches from the inside edge of the big flexor tendon which runs through the back of the rear leg.

The perpendicular edge of bone, on the outside of the horse’s hock, has been called by horsemen, over eons of time, the “curb bone.” This horseman’s term has no reference to the term or condition known as
a “curb.”

As your hand journeys down the outside or lateral portion of the hock your fingers should reach the bottom of the bony ridge on the tarsal-metatarsal joint and be about 1-½ inches from the big tendon on an 1,800 lb. drafter. If the bony ridge continues up to or over the tendon, this condition is known as a “curby hock” and the animal is called a “curby horse.”

“So what?” some say. Well, a curby horse is unsound and, apparently, the condition is inherited.

Why is the curby horse undesirable? The answer is simple. As the bone grows over the big deep and superficial flexor tendons, it will prevent the animal from raising its rear leg. This will result in loss of power, locomotion and action.

I was asked one time to look at a big Percheron gelding whose problem was that it couldn’t trot. The examination revealed the hock bone had almost completely grown over the flexor tendons on both legs. Although he could walk, it was extremely difficult for him to trot.

The cases of curby horses are on the rise. The condition seems to be inherited and I firmly believe some judges are lax in spotting it. I also suspect there are many horsemen who don’t know the first thing about a curby horse.

An animal with curby hocks, or one with curbs, has absolutely no place in one’s breeding stock. Pay close attention to the hocks of those animals which you intend to buy as well as those you may be asked to judge in the show ring.

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