There are so many things attract us to horses. We love their spirit. We celebrate the speed of race horses and the strength of the draft breeds. We are amazed by the extreme athleticism of sport horses. We love our horses’ willingness to enter into partnership in our activities. Best of all, most seem to be pretty happy just hanging out with us. Besides all these qualities, there are also some anatomical characteristics of horses that are either unique or finely tuned as compared to others in the animal kingdom. This article will focus on some unusual characteristics of the horses head.
Our eyes are on the front of our head. As a result, unless we turn our neck or body we are always looking forward. This is true of all animals that are hunters. Lions, dogs, and cats all have this type of eye arrangement. It gives us great depth perception and focus
Horses’ eyes are set on the side of the head, which is true for all the prey or flight animals. This would include the giraffe, antelope, and rabbit. Having the eyes to the side is the perfect arrangement for the hunted as it gives them almost wrap around vision. They can see a full 350 degrees out of 360 without turning their head. The only limit to their vision is the few feet directly in front of them and the few directly behind. This is pretty important when something is looking to have you for lunch. It is also something for us to remember when we are back by their hip. A horse might seem to be looking straight ahead, but can very accurately throw a foot your way. Horses have color vision, but it is not as refined as ours. For this reason jumps should be painted in bright colors, and for your safety the rails should not be painted in earth tones unless you’d like to wear some (earth, that is). Finally, the night vision of horses is far superior to ours. Go out into their pasture some very dark night when you can’t see a thing. You might well bump into a horse, but they will never bump into you.
Horses also have an exceptionally long soft palate. When your horse has a speculum in its mouth to have its teeth worked on, ask to take a look. You’ll be able to see all the teeth, but not as far back as the pharynx where the swallowing happens. Their elongated palate actually rests on top of the tongue, blocking the back view. When food like dry beet pulp gets stuck part way down the esophagus on the way to the stomach, the horse is “choked.” Horses are continually producing huge amounts of saliva. The saliva in a choked horse gets swallowed, but doesn’t make it to the stomach. It hits the obstruction and as more saliva is produced it backs up, against gravity, all the way back up to the back of the mouth. That long soft palate prevents it from coming out of the mouth, so it continues up and starts to spill out of the nose as froth when it mixes with the air. It’s sort of like Coke coming out of your nose if you have a mouthful and start to laugh. To relieve the choke your veterinarian may have to pass a stomach tube through the nose into the esophagus to alleviate the problem. It can’t be done through the mouth as that long palate would be in the way again.
Another unusual feature of the horses head is the paired “air sacs” called the guttural pouches. About the only other large animal known to have these pouches are rhinos and tapirs. The pouches are just to the side of the large space, called the pharynx, at the back of the mouth. In a 1000 pound horse their capacity is between 2 and 4 cups each. It is thought that their purpose is to equalize different pressures within the head. Running through each pouch is one of the large carotid arteries which supply blood to the brain. Some researchers feel that the air in the pouches cools the blood in those arteries. In this way the air in the pouch acts like a radiator.
Guttural pouches can be trouble. After a horse has the messy upper respiratory disease that we call strangles and has recovered, the strep bacterium that causes it can hide out in the pouches. Some horses will carry the bacteria there for months. This makes them a source of infection for other horses.
The pouches are also an ideal place for molds to grow. One of the places the mold settles on is that large exposed carotid artery. The mold has the potential of eating into and eroding the wall of the artery and causing it to rupture. This is like puncturing a fire hose that is pumping water. The bleeding can be so severe that horses have been known to bleed to death out through the nose. Most nose bleeds have other causes and are not as serious, but it is good to check with your veterinarian who may want to do an endoscopic exam if you have a horse that is dripping blood for an extended period of time.
The next article of this series will focus on a few more characteristics of horses that make them unique in the animal kingdom.
–David A. Jefferson, DVM