Jul 11 2010
Teeth The Cause Of Many Horse Health Problems Part Two
Next the tongue, cheeks, and palate must all function in synchronous harmony. The extremely muscular tongue and cheeks function opposite each other to position the feed bolus between the upper and lower arcades for optimum grinding efficiency. Also, the hard palate is strongly ridged in an alternating pattern to act as an auger, keeping feed moving from front to back. If you have ever seen a horse try and spit something out, you understand how hard it is to override this strong front-to-back mechanism.
Once the properly chewed feed bolus reaches the back of the mouth (the oral pharynx), it is carried out down the esophagus, continuing to the next stage of digestion. If you watch a horse eat, you will see him grinding with his jaws rhythmically moving side to side. Periodically the motion stops. This is generally when he’s swallowing. There is a furrow that runs the length of the horse’s neck near the front. This furrow contains the large jugular vein, the carotid artery, as well as the esophagus. You can actually observe the feed bolus move all the way down the esophagus if you very closely watch the left side of the horse’s neck in the groove during this momentary break in chewing.
Summarizing, the lips select the feed and move it into the mouth. Other soft tissues conduct the feed through the mouth, enabling the grinding teeth to pulverize it, mix it with saliva, and move it to the rear of the mouth for swallowing.
Sounds straightforward, right? On one level it’s simple. But when you begin to examine the many mechanistic elements involved in the process of chewing and preparing stemmed roughage for swallowing, a way more complicated, though no less sophisticated, apparatus emerges.
Specialty Teeth
The next conceptual step is that regarding biomechanics. The horse and other herbivores, due to their extremely different diets, have evolved with specifically adapted teeth plus a very effective chewing pattern to break down the coarse ration. Their teeth are termed hypsodont. That is they have got large crowns, and the majority of each crown remains deeply embedded in the bones of the skull and jaw, erupting a few millimeters every year to replace the same amount as it is worn away on the chewing surface. But horses don’t produce new tooth material. There’s a finite quantity of tooth to last the horse’s lifetime.
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They chew in a roughly elliptical pattern that utilizes crushing forces in a side-to-side motion. There’s also an important, although smaller, forward and backward component to the pattern, but it is much less obvious to the casual observer. If you were to spend a bit of time watching your horse eat his hay or pasture grass you will see that his lower jaw opens then moves toward one side or the other, then simultaneously closes and moves back toward center. Due to this powerfully “sided” movement, horses are only able to chew on one side of their mouth at a time. This last motion, because the jaw closes and moves the lower cheek teeth strongly across the uppers, is very effective at breaking, tearing, and grinding stemmed roughage.
The health of the system–in addition to the type of feed the horse eats–determines the number of grinding strokes needed to produce a feed bolus which is safe and appropriate to swallow. A horse with compromised dentition might take much longer to chew his feed. Fortunately for the horse, the masticatory equipment and also the larger digestive system have a lot of potential for compensation. One part of the system can make up for deficiencies in another.
For instance, new studies have revealed that horses do not necessarily need to grind roughage perfectly so as to get the needed nutrition. The lower digestive tract is apparently capable of extracting nutrients from a variety of chewed particle sizes. There is, obviously, a critical limit to this compensatory capability. The horse must able to chew roughage well enough to swallow the bolus. Extremely coarse stems cannot be safely swallowed, and the horse might “choke” if he tries to swallow poorly chewed feed.
Continued in Part Three…
Referneces
