The common perception of equine dentistry is that horse’s teeth need to be filed so that they can eat hay, grass and grains efficiently and to remove sharp hooks and ridges. While all of this is most certainly true, much more lies in the balance of the horse’s jaw.
Mastication – chewing, that is – not only pulverizes the food into particle sizes needed for proper digestion, the action in combination with the correct level of pressure in the mouth is the major signal to the body to produce saliva. Saliva is the second step of digestion, the one following ingestion/chewing and preceding breakdown by acids in the stomach for release of calories and nutrients. Many vitamins and minerals are better absorbed in the esophagus pre-acidification and the proper amount and pH of the saliva is key to releasing these from the feedstuff. Saliva is furthermore of paramount importance in keeping the digestive tract lubricated. There is no horse owner that does not have a healthy respect, bordering on fear, of colic.
The most common cause of fatal colic in horses is an impaction. The food or foreign body becomes “stuck” in the intestinal tract and adheres to the wall of the gut, causing tissues to die and/or total blockage. Dehydration is a known villain, leaving the horse’s digestive system ripe for this failure. The link that is often missing is that the gut needs to remain lubricated by saliva, not simply fluids travelling by osmotic balance. Of course, Horse Maintenance 101 tells us to keep that water available at all times, monitored and doled out in portions to a hot or sweaty horse. This is the most important health consideration there is; however, proper digestive utilization of this water depends on long term salivary health.
Older horses losing teeth and suffering compromised jaw motion often require creative methods of hydration to keep them going, e.g. soaking feeds to pre-wet them and sometimes even IV support. Competition horses can also become quite prone to impaction if their jaw motion is compromised during competition, such as having the mouth tied shut with a flash or tight noseband. Dental balancing of the motion of the mouth, from the incisors (front teeth) through the back of the jaw is necessary to help the horse maintain their perfect chewing motion, thus stimulating all of the salivary glands equally, with none receiving too little pressure as not to produce, or too much as to become inflamed and the ducts close and become painful. Overproduction of saliva is possible by excess pressure of even as little as one tooth, which can also cause dehydration and lead to colic.
The next major cause of colic with dental implication is gas colic. The function of the digestive system is dependent on a delicate balance of very harsh acids that must stay where they are needed, and muscles to move the food slowly, ever onward as well as super porous, delicate stomach lining to allow all of the nutrition available from the food to pass into the bloodstream and be used. The saliva, as mentioned above, provides much-needed lubrication to this process. It also starts digesting the food matter with a cocktail of enzymes, as well as premixing the food to a pH that will aid in breakdown by the acids of the stomach. If the enzymes are not present in the saliva, due to less than healthy salivary output or a pH that will not support them, the stomach is presented with unprepared food. This would be similar to food that is unchewed as well. Please note at this time that in an herbivore that is unable to regurgitate (throw up) their food this is a very serious problem; far more serious than say a cat or dog now chewing properly, as their digestive make up is much more elastic and forgiving. The stomach may have enough acid to cope with the unprepared food somewhat and it will do its best to extract from the food what it can, but peristalsis marches ever forward, carrying the food out of the acid chamber into the intestine. If the stomach was struggling with unprepared food, often the partially digested food will cause discomfort as it heads into the very delicate tissue of the small intestine. This causes symptoms visible to most horse owners of pain and distress. Internally the horse is experiencing gas and may also be having breakdown on a cellular level, causing the wall of the lining of the stomach to ulcer. While there are admittedly many causes of ulcers in horses, stress being high on the list, pH imbalance in the gut is a very common one. Gas in the intestine can lead to such pain and distress that it is often thought to cause the horse to roll violently and create a torsion, or “twist” colic.
While there are times that we cannot achieve balance in the mouth to sustain ideal saliva, as in older or injured horses, it is one of the basic necessities we are meeting by performing a comprehensive routine dentistry. The mouth is the gateway to digestion and its importance is not all in the mechanics of chewing. For therapies to aid in the digestive process for older or compromised horses, please see our article, complete with feed and probiotic recommendations, The Aged and/or Compromised Horse.