One of the oldest of adages in the horse world is, "No feet, no horse." We could add another that is just as appropriate, "No teeth, no horse." The teeth are one of the most important parts of a horse's anatomy, yet they often are neglected. Many horse owners make regular trips to the dentist to have their teeth cleaned, cavities filled, and, in some instances, a tooth extracted. Yet, for many, it is very easy to neglect routine care for their horses' teeth.
Regular routine dental care is the best safeguard against tooth problems. This might involve examining and treating horses with problems every six months.
Actually, a horse uses its teeth more than a human does. Many humans eat three meals a day at spaced intervals. By contrast, horses in the wild and on pasture might spend 10-12 hours per day grazing. The same is true of horses in paddocks or box stalls on free choice hay. They will eat a little at a time, but will be munching often.
Humans have interfered with the horse's normal pattern of existence. Many confined horses are fed a highly charged ration that is consumed in two or three short eating sessions per day. They quickly consume the food and spend the rest of the time in boredom and can develop bad habits, such as wood chewing or stall walking and weaving.
Despite neglect on the part of some, there has been an increase in dental awareness among horse owners in recent years, says Jack Easley, DVM, MS, Diplomate ABVP, of Shelbyville, Ky., a practitioner who devotes a good deal of his time to dental care of equines. Easley also presented a paper on "Equine Dental Development and Anatomy" at the 1996 American Association of Equine Practitioners meeting in Denver, Colo.
Several factors are involved in the demand for more equine dental care today than in the past, according to Easley.
"First, we continue to make more performance demands on younger horses before they have completely developed permanent dentition (one-to four-years-old)," he says. "Second, there is an increased demand for middle-age performance horses for dressage, saddle seat, hunting, and driving (eight- to15-year-olds). Third, horses are being kept in production because of improved reproductive technology, i.e., embryo transfer and semen preservation (14- to 24-year-olds). Fourth, older geriatric horses are being retired to the farm or used for pleasure riding rather than being sent to slaughter. Fifth, feed savings from good dental care become more of a factor as human and equine populations increase globally."
To understand better the need for proper dental care, we first have to understand something about the unique tooth structure of the horse and the way in which it evolved as horses slowly changed from an animal which was only about 26 inches tall to the 1,000-pound horse of today. Obviously, that great increase in size over time has put greater demands on the horse's digestive system and its ability to crop food from growing grasses, plants, and shrubs.
"It has been shown during the evolution of Equus caballus," says Easley, "that, with an increase in size, there is a cube factor in the increase of food required. A doubling of height requires eight times the food intake. The amazing grinding system of the horse's teeth accommodates such an increase in food intake and processing."
As the equine evolved, it developed into a continuously grazing animal.
Easley describes some of the changes that occurred during this evolutionary period:
"Increased speed and stamina evolved with the reduction in number of limb bones...With this increased athletic prowess came other body system modifications that the masticatory system had to accommodate. By continually grazing small quantities of food, the equine evolved an oral cavity that was kept small in relation to the nasal and nasopharyngeal structures, allowing more room for respiratory functions. The hind gut fermentation of forage reduced the bulk in the abdominal cavity and did away with the need for regurgitation and rumination.
"This is advantageous to the survival of the horse from the standpoint of not needing to stay in one place to ruminate. As a result, the horse was always ready to flee from predators. The downside of this adaptation is that forage had to be processed in the mouth on one pass, making proper mastication of forage extremely important.
"Elongation of the head and neck and the modification of skull shape have allowed for pastural grazing with the wide-set orbits keeping a watch for predators."
As the tooth structure of the equine continued to evolve, changes occurred in the way equines masticated food. For one thing, the horse developed a side to side chewing movement with the grass and other food being ground between the upper and lower cheek teeth after having been sheared by the incisors.
The type of incisors and molars developed by the horse are hypsodont. Simply put, this means that the teeth are constantly erupting as the grinding action wears away the crown surface. To further simplify, the tooth can be likened to a piece of chalk. As one writes on the blackboard, the chalk is worn away and, after a time, becomes so short as to be useless. It is much the same with hypsodont teeth. They keep erupting or growing throughout the horse's lifespan. Because they are not continually replenished as to length, the time comes when only stubs remain and the old horse might have difficulty masticating its food.
A four-year-old horse, for example, might have 4 1/2 inches of tooth, while the 20-year-old might have only a half inch.
Because a horse's teeth function appropriately only when they are able to come into direct contact over the entire two opposing surfaces, it becomes immediately apparent that any ridges or points that develop from uneven wear are going to have a detrimental effect on the horse's ability to shear forage and chew it.
Before we get into some of those problems, however, let's take a look at the teeth as they develop from infancy into equine adulthood.
When a foal is born, it normally has no teeth, but that lasts for only a few days. Within the first week of life, the foal will develop four incisors--two in the upper jaw and two in the lower. These are the central incisors. The second, or intermediate, set will erupt within the first couple of weeks, and the final set, the corner incisors, will arrive at about six months of age.
A few weeks after birth, the foal also will erupt three cheek teeth or premolars in each dental arcade (side of jaw), which translates into six uppers and six lowers. Thus, a full set of baby teeth totals 24--six upper and six lower incisors and six upper and six lower premolars.
Eventually, all of these baby (deciduous) teeth will be replaced by permanent teeth.
"There is a lot going on inside a horse's mouth between the time he's six months old with a full set of baby teeth," says Easley, "and when he is four to 4 1/2 years old. By that time, all of the baby teeth have been replaced with permanent teeth, plus there are 12 additional molars."
Because the baby teeth, also referred to as caps, are shed in the order in which they arrive, they provide a definitive yardstick for determining a young horse's age. The central upper and lower incisors are the first to go when the young horse reaches about 2 1/2 years of age; the intermediate incisors will be lost at about 3 1/2, and the corner incisors at about 4 1/2 years of age.
With the premolars, the rate of shedding is about the same-the first set will be shed at about 2 1/2 years of age, the second set at three, and the final premolars at about four years of age.
The baby teeth have short roots and are designed to be pushed clear by the erupting permanent teeth. When all goes well, that is exactly what happens and the horse's lifestyle is not interrupted. However, things don't always go as they should.
Sometimes a baby tooth breaks in half and becomes lodged in the gum. And, sometimes baby teeth become loose, but won't shed, thus trapping the erupting permanent tooth in the jawbone. When that occurs, the horse usually will develop a knot on the lower jawbone as the bone remodels to make way for a tooth that is supposed to be erupting through the gum, but isn't.
Because of these and other potential problems, Easley recommends that a young horse should have its mouth examined every six months. Normally, he says, a baby tooth that doesn't shed is easily removed with forceps. Once the baby tooth is removed, the trapped permanent tooth can erupt and the knot on the lower jaw will disappear as the jawbone once again remodels.
Loose, retained baby teeth can cause a great deal of discomfort for the horse, says Easley. The discomfort often is manifested by irritability on the part of the horse, bad odor from the mouth, and sometimes behavioral problems, such as head tossing and refusing to respond to the bit.
The only solution when a retained baby tooth is the root of a training problem is extraction of the tooth.
Also capable of causing training problems are wolf teeth. They are two short-rooted teeth located adjacent to the first premolar in the upper jaw. Wolf teeth normally erupt when a horse is between 12 and 18 months of age. Easley recommends that they be removed, particularly if the horse is to be used for performance.
"Wolf teeth sit in a precarious position in the mouth," he explains. "Depending on where they are located--on the inside of the cheek teeth or the outside--they can cause difficulty with bitting. A snaffle bit can cause the cheeks to roll back against the wolf teeth in a painful and irritating fashion. The wolf teeth may also be contacted by the bit and loosened because their root structures aren't very long. This will also cause irritation to the horse. Many trainers and owners, when they start bitting a horse, routinely have wolf teeth removed, which is something I recommend. Taking them out simply eliminates a potential complication in training."
Back to the shedding and replacement process.
The permanent teeth that replace the baby teeth are the kind that many humans would love to own when visiting the dentist to have a cavity drilled out and filled. The exposed crown of an adult horse's permanent tooth has neither a central nervous structure, nor a blood supply. Thus, when it is treated, the horse feels no pain.
We already have discussed the fact that a horse's tooth is hypsodont. In humans, the crown of a tooth extends only to the gum line. With the horse, the crown extends nearly four inches into the jawbone. Only about one-fourth inch of a 4 1/2-inch equine tooth is root.
In the beginning, the permanent tooth has a pulp chamber, but by the time the horse is 4 1/2 years old, the chamber has receded and finally has been closed off at the base of the tooth.
"It isn't a dead tooth," says Easley, "but there are no nerves and no blood supply up through the central portion of the tooth. They have receded down into the root and, basically, the root has just closed off."
The adult horse, assuming that it has had wolf teeth removed, has six upper and six lower incisors, six upper and six lower premolars (the most forward set of cheek teeth), and six upper and six lower molars (the cheek teeth at the rear of the mouth), plus two upper and two lower canine teeth just behind the incisors. Females normally have the same complement as males, minus the canine teeth.
Throughout the horse's life, its teeth are pushed upward from the lower jaw and downward from the upper as the surface of the crown within the mouth is worn away.
This wearing away takes place as the horse chews. When the horse chews, its lower jaw, which is somewhat narrower than the upper, moves back and forth laterally, grinding the food as lower teeth come into contact with the uppers. As long as there is full lateral movement or excursion of the jaw, normal teeth will wear off evenly. When there isn't full excursion, they tend to wear unevenly, and that can produce problems.
Many dental problems faced by horses essentially are man-made through genetics. We often breed horses which have dental problems and thus pass those problems on to future generations. If a horse in the wild couldn't crop and chew grass properly, it eventually became weak from starvation and either died or became a victim to a predator.
In a domestic setting, there is no quick death verdict for a horse with bad teeth. Dental problems can be coped with and the horse can perform and reproduce throughout a relatively long life.
In today's world, horses which are born with normal teeth can develop dental problems because of diet and frequency of feeding. When eating hay from a manger, for example, a horse doesn't use its incisors as it does when grazing. Instead, it pulls the hay into its mouth with its lips and grinds it up with the cheek teeth--premolars and molars. As a result, normal cheek teeth will wear down, but there is nothing to wear down the incisors.
Eating grain or processed feed also can cause dental problems for horses, only this time with the cheek teeth involved in a negative way. The difference between a horse's eating grass or hay as opposed to grain or pellets, says Easley, is similar to comparing a human's eating shredded wheat cereal as opposed to peanuts.
When a person is eating shredded wheat, all of the teeth would be engaged in what he describes as a "big wide chew" or full excursion. With peanuts, there would be a "little, tight chew" or limited excursion.
The big, wide chew causes normal upper and lower teeth to grind against each other--surface to surface--and, as a result, to wear down evenly; while the little, tight chew, with limited lateral movement of the lower jaw, often results in uneven wear. The problem is magnified if the horse has abnormal teeth to begin with.
"A horse has to have wide lateral excursion of the jaw to keep the entire surface ground off," explains Easley. "If you limit the lateral excursion, you start getting points or ledges on the inside of the lower teeth and on the outside of the upper teeth. If the ledges are small, it is no major problem. But, remember that the horse has 4 1/2 inches of tooth to erupt. Over time, the points and ledges get larger and larger. As they get larger, excursion of the jaw becomes more limited, and the horse is no longer able to properly masticate its food."
Easley estimates that there are dental problems with approximately 25% of today's equine population. Many of the problems result from malocclusion of the teeth. Simply put, malocclusion occurs when the upper and lower teeth of a horse do not meet properly in the cropping or grinding process. A horse with malocclusion can't properly masticate its food.
Horses with malocclusions can wind up with ledges as much as a quarter-inch in height. When the animal reaches that stage, its ability to masticate food of any kind is severely compromised and secondary problems like colic can arise.
A full excursion of the jaw also is involved in helping a horse keep its teeth clean.
"Horses don't have to brush their teeth like we do," says Easley, "because they normally don't have any tartar buildup as long as they have wide excursion. However, when excursion is limited, they tend to get feed packed between their teeth. Then you start getting gum disease and the loosening of the teeth--gingivitis and periodontal disease. The process starts gradually and, over a period of years if the cycle isn't broken, the horse gets to a point where it no longer properly digests its food because it can't masticate correctly."
It often is at this point that one can observe whole grain and long stems of hay in the fecal matter.
Regular, routine dental care is the best safeguard against tooth problems. This might involve examining and treating horses with problems every six months. At the least, it ought to encompass a routine, annual dental exam. If the examining veterinarian finds points, hooks, or ridges resulting from malocclusion, he or she normally will remove them by floating the teeth--filing down the offending edges with a specially designed rasp-like tool.
A foal, Easley says, should have its mouth examined by a veterinarian as part of a routine postnatal examination.
"At this point," he explains, "you can detect various congenital defects. There are steps that can be taken, such as braces or the use of wires, to correct certain problems when the horse is young. If you wait until the horse is a 1 1/2 years old, the growth spurt is already past and it is too late. One should always remember, however, that these types of problems are hereditary and, if we use such a horse for breeding, we are enlarging the malocclusion gene pool."
The young horse with normal teeth should be given another thorough dental exam when it reaches 12 months of age, Easley believes. If the horse has good occlusion, no treatment should be necessary. However, if there is malocclusion that has resulted in sharp points or ledges, they might have to be removed by floating (filing) the teeth.
The next time a routine dental exam is needed, he says, is when the horse is bitted for the first time, often at 18 months of age. This is the time when wolf teeth are identified and, if they seem to pose a problem, are removed.
This also would be the time when any rough or sharp edges at the front of the first set of premolars would be rounded off. In some horses, this might need to be done every six to 12 months as the teeth continue to erupt and sharp points or edges reappear and cause irritation when contacted by the bit.
Although a majority of the malocclusion problems are with the cheek teeth--premolars and molars--problems also can involve the incisors. If the horse doesn't wear down the incisors, those teeth might prevent the cheek teeth from coming together properly.
Another problem that can involve the incisors is parrot mouth, a condition where the upper incisors overlap the lower. This inherited condition makes it difficult for a horse to crop grass--in the worst cases, parrot mouth makes it impossible for the horse to graze. This means there is nothing to wear down the incisors and they grow unimpeded and have to be filed down on a regular basis.
There is a bit of good news for the horse when its teeth are floated--zit feels no pain. The process would be akin to a human cutting off excess fingernail growth.
The dental problems faced by today's domesticated horses aren't new. Easley says that a 1910 study in England that examined the skulls of a number of horses to determine the state of dental health found that many of the problems that exist today existed then. The difference is that a growing number of today's horse owners tend to be much more cognizant of, and responsive to, their horses' dental needs.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
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