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The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.

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There’s a popular quote in the horse world that goes something like, "A horse was designed by a committee." Never has a quote been more accurate.

Horses are structurally built to not survive and how they managed to evolve for millions of years and still be here today is a fascinating mystery to me. But I’m glad they’re still here. They are awfully pretty to look at and downright fun to ride.

A horse’s anatomy simply does not make sense. Most of their digestion of dietary roughage occurs in the hindgut, way after the absorption of nutrients occurs in the stomach. The angle at which their esophagus enters the stomach is so extreme that horses cannot physically vomit. Their large colon has a hairpin turn called the pelvic flexure, which is so tight that it is a frequent location for blockages. And lastly, there are horse feet. Do I really need to say anything more? They don’t say "no hoof, no horse" for nothing.

Actually, the equine hoof is an engineering marvel. The average horse weighs about one thousand pounds and has a hoof with a diameter of approximately six to eight inches. Now, if I were good at physics, I could calculate for you the amount of force that is exerted on each hoof, but my skills in physics are embarrassing at best (E=mc what?). Therefore, I will sum it up in non-physics terms: There’s a lot of force on those small hooves.

I often feel that people don’t understand exactly how a horse’s hoof is connected to its leg. Obviously, there is a bone in there, but how is it situated? The answer lies in very cool structures called laminae.

Let’s take a step back for a minute.

From the outside, you have the hoof, a somewhat rigid structure that bears the horse’s weight. On the inside, you have a pyramid-shaped bone, which is called the third phalanx (P3) in anatomical terms, but it also goes by the names coffin bone and pedal (pronounced "pee-dal") bone. This bone is suspended inside the hoof capsule by these laminae, which are delicate interdigitating tissues that act like Velcro to connect P3 to the inside of the hoof.

 horse hoof, hoof anatomy, laminitis, lameness in horse, horse founder

Cool, right? These laminae are highly vascular and extremely sensitive to what’s going on with the rest of the horse’s body. As you may guess, laminitis, the scourge of horse feet, is an inflammation of these very laminae. Laminitis is extremely painful and, unfortunately, can be deadly.

The common name for laminitis is founder. Any large animal vet sees a lot of founder cases during the spring due to the rapid growth of lush grass. It’s often weird to think how eating grass can affect a horse’s hooves, but here’s how: Rich spring grass is full of complex sugars. When a horse is grazing on this grass and its digestive system is not used to it (like in the spring after the horse has been living on hay all winter), this new diet is a shock to the horse’s metabolism. The laminae, due to their intricate blood supply, are extremely sensitive to changes in metabolism and begin to become inflamed and die. This causes a disruption in the support structure of P3 and as a result, the bone begins to detach from the hoof wall and physically rotate or sink downwards. This is extremely painful, as you may imagine. Once there is movement of P3 (diagnosed by hoof radiographs), there’s no treatment (since you can’t put the hoof back where it is supposed to be), so your only goal is to make the horse as comfortable as you can until its feet grow out and repair themselves. There are some special ways to trim the hooves, along with specialized boots and support devices to put on the hooves in the interim.

Sadly, sometimes movement of P3 is so severe that it is impossible to repair the damage. Occasionally, the bone actually penetrates through the bottom of the hoof. This is serious stuff.  Remember the racehorse Barbaro, winner of the Kentucky Derby in 2006? He was euthanized as a result of laminitis. It should be no surprise that the "f-word" in equine medicine is founder.

On a positive note (if there is one when dealing with founder), I’ve had many cases where I dreaded looking at the radiographs, thinking the rotation of P3 would be horrendous, and it wasn’t.  Also, I have yet to euthanize a horse due to laminitis. Although the recovery period may take months, so far my patients have survived thanks to some luck and the hard work and patience of their owners.

So cheer up, dear horse lovers! Even though we weren’t consulted when the horse-designing committee was in session, we have learned to deal with their mistakes. And at least they got the aesthetic appeal of the horse correct.

Dr. Anna O’Brien

Image: ninocka / via Shutterstock

Comments  3

Leave Comment
  • Wow!
    03/30/2012 07:31am

    Absolutely fascinating!

    It's hard to comprehend that eating grass in the springtime can cause such problems.

    It's also a little hard to comprehend how horses can run so swiftly.

    Thank you for a great post, Dr. O'Brien.

  • I also say Wow!
    03/30/2012 05:26pm

    Fantastically interesting, Dr. O'Brien!

    When I was young, like many girls, I was "horse crazy."

    I never did get to own a horse, but still love them and am fascinated by information of all sorts about them.

    So, how does a horse owner go about transitioning their animal to grass to avoid this problem, I wonder.

    Thanks for your great posts about large animal medicine!

  • Founder Article
    03/31/2012 03:11pm

    Not sure of where to post this, but I did not receive this article in my email. Please update. Thank you.

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