Horse teeth
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Horses' teeth are often used to estimate the animal's age, hence the sayings "long in the tooth" and "Don't look a gift horse in the mouth".
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[edit] Types of teeth
At five years of age a horse has between 36 and 44 teeth. All horses have
- Twelve premolars and twelve molars commonly known as cheek teeth or jaw teeth.
- Twelve incisors, or front teeth.
Additionally, a horse may have:
- Between 4 and 5 canine teeth (tushes, tusks) between the molars and incisors. Generally all male horses have four canines. However, few female horses (less than 28%) have canines, and those that do usually have only one or two, which many times are only partially erupted.
- Between zero to four wolf teeth, which are vestigial premolars and not canines as the name may suggest. About 13-32% of all horses also are born with wolf teeth, with most of those having only one or two. They are equally common in male and female horses and much more likely to be on the upper jaw. If present these can cause problems in the bitting of the horse as they can interfere with the horse's bit contact, and may also make it difficult to rasp the second premolar. Therefore, wolf teeth are commonly removed.
[edit] Tooth growth
A horse's incisors, premolars, and molars continuously grow throughout the animal's life, to provide new material as the grinding surface is worn down from eating. A young adult will have teeth which are 4.5-5 inches long. Only about 1/4" will have erupted at this point, with the majority remaining in the dental socket. The rest of the tooth will slowly emerge from the jaw, erupting about 1/8" each year, as the horse ages.
Canines do not continue to erupt throughout the horse's life. Therefore, they may become sharp since they have nothing to rub against, and should be filed down until dull.
[edit] The teeth and the bit
Contrary to popular belief, the bit of a bridle is not held between the horse's teeth, but lies in the "interdental space." This space lacks teeth, providing an area for the bit to rest without forcing the jaws open, and occurs between the cheek teeth and the incisors (or canines, should the horse have them).
However, if the bridle is adjusted so that the bit rests too low, or (more commonly) too high, it may push against the teeth and cause discomfort.
Sometimes, a "bit seat" is filed in the first cheek tooth. A veterinarian rounds the surface, so that, when the bit is pulled, the flesh of the cheek is not pushed into the sharp edge of the tooth. Although this practice is disputed, and most agree that an extreme bit seat can indeed be harmful, many veterinarians believe it makes riding more comfortable for the horse.
[edit] Estimating age using the teeth
It is possible to age a horse using signs of the tooth eruption and wear. However, this is not an exact science, and become increasingly difficult after the horse is "aged." Horses are individuals, and two horses of the same age may have difference wear patterns.
[edit] Estimating age using tooth eruption
There are 24 deciduous teeth (also known as milk, temporary, or baby teeth). These come out in pairs, and are pushed out later by the permanent teeth. The number of permanent teeth may vary, depending on if the horse has wolf teeth or canines. Most mares have 36, and most male horses have 40.
| Type of tooth | Number | Deciduous | Permanent |
|---|---|---|---|
| Incisor | First (central) | birth to 8 days | 2.5 yrs |
| Incisor | Second (intermediate) | 4.5-6 weeks | 3.5-4 yrs |
| Incisor | Third (corner) | 6-9 months | 4.5-5 yrs |
| Canine | Absent | 3.5-5 yrs, some around 6 yrs (if ever) | |
| Premolar | First (wolf) | Absent | 6 months to 3 years (if ever) |
| Premolar | Second | birth to 2 weeks | 2-3 yrs |
| Premolar | Third | birth to 2 weeks | 2.5-3 yrs |
| Premolar | Fourth | birth to 2 weeks | 3-4 yrs |
| Molar | First | Absent | 9-12 months |
| Molar | Second | Absent | 2 yrs |
| Molar | Third | Absent | 3-4 yrs |
By age five, all permanent teeth have usually erupted. The horse is then said to have a "full" mouth.
However, individual horses will vary, and some breeds and types of horses are known to have differing eruption timelines. These include:
- Shetland ponies: The middle and corner incisor (both deciduous and permanent) usually erupt later than the average horse.
- Draft horses and miniature horses: the permanent middle and corner incisors usually erupt later than average.
[edit] Estimating age using wear patterns
After eight years, indeed good authorities say after five years, the age of a horse can only be conjectured. Dishonest dealers sometimes "bishop" the teeth of old horses, that is scoop them out, to imitate the mark: but this can be known by the absence of the white edge of enamel which always surrounds the real mark, by the shape of the teeth, and other marks of age about the animal. The wear of teeth may also be affected by diet, natural abnormalities, and cribbing.
- Cups: are hollow and rectangular or oval in shape, appearing on the tables of the permanent incisors, that wear away over time. In general, cups are worn away on the lower central inscisors by age 6, the lower intermediates by age 7, and corners at age 8. The cups of the upper central incisors are worn away by 9 years of age, the upper intermediate incisors by 10, and the corners by 11. When all the cups are gone, the horse is referred to as "smooth mouthed."
- Pulp mark/Dental star: After some wear has occurred on the teeth, the central pulp cavity is exposed, and the tooth is marked by a "dental star" or "pulp mark." These begin as a dark line in front of the dental cup, which grows in size and becomes more oval in shape as the cups are worn away. Dental stars are usually first visible at age 6, on the animal's lower central incisors, and very visible by age 8. They appear on the lower intermediates by age 9, and on the other incisors between the ages of 10-12 years.
- Hook/Notch: A hook appears on the upper corner incisor around age 7, and disappears by age 8. It reappears around age 13, again disappearing about 1 year later.
- Galvayne's Groove: The Galvayne's groove occurs on the upper corner incisor, producing a vertical line, and is helpful in approximating the age of older horses. It generally first appears at age 10, reaches half-way down the tooth by age 15, is completely down the tooth at age 20. It then begins to disappear, usually half-way gone by age 25, and completely gone by age 30.
- Lower jaw shape: Older horses may appear to have a lean, shallow lower jaw, as the roots of the teeth have begun to disappear. Younger horses may seem to have a lumpy jaw, due to the presence of permanent teeth within the jaw.
- Angle and Shape of the incisors: As the horse ages, the angle of the incisors generally becomes more acute, slanting forward. The incisors gradually change their form as the horse ages, becoming round, oval, and then triangular.
[edit] Dental problems
Like humans, horses can develop a variety dental problems, some which may be very serious and require surgery. It is therefore important that horse owners have a veterinarian check their animals' teeth regularily, to head off any potential issues, and examine the teeth should the horse exhibit any signs of dental problems. Abnormal teeth not only affect the horse's comfort while chewing, but also commonly manifest themselves as disobediences while the animal is ridden.
[edit] Problems due to wear patterns
Many dental problems in horses are related to the fact that their teeth grow continuously throughout their life. Horses are evolved to graze nearly continuously, often on rough forage in semi-arid climates. Their teeth are designed to wear against the tooth above or below as the horse chews, thus preventing excess growth.
There are many times when tooth wear is not even, and the horse may develop sharp edges on their teeth that reduce chewing efficiency of the teeth, interfere with jaw motion, and in extreme cases can cut the tongue or cheek, making eating and riding painful.
In the wild, natural foodstuffs may have allowed teeth to wear more evenly. Because many modern horses often graze on lusher, softer forage than their ancestors, and are also frequently fed grain or other concentrated feed, it is possible some natural wear may be reduced in the domestic horse. On the other hand, this same uneven wear in the wild may have at times contributed to a shorter lifespan. Modern wild horses live an estimated 20 years at most, while a domesticated horse, depending on breed and management, quite often lives 25 to 30 years. Thus, because domesticated animals also live longer, they may simply have more time to develop dental issues that their wild forebears never faced.[citation needed]
Hooks, or sharp points on a tooth, usually develop on the outside of teeth in the upper jaw, the inside of teeth in the lower jaw. They also commonly occur on the front of the first upper premolar, or last lower molar.
A step mouth occurs when one cheek tooth grows longer than the others in that jaw. This is usually due to the fact that the tooth opposing that particular one, located in the opposite jaw, was missing or broken, and therefore could not wear down its opponent.
A wave mouth occurs when at least two of the cheek teeth are higher than the others, so that, when viewed from the side, the grinding surfaces produce a wave-like pattern rather than a straight line. This can make chewing very difficult for the horse.
A shear mouth occurs when the grinding surfaces of the cheek teeth are severely sloped on each individual tooth (so the inner side of the teeth are much higher or lower than the outer side of the teeth). This may result in an angle at 60-75 degrees, opposed to the normal 15 degree angle seen on most horses. Again, the chewing motion is severely affected.
[edit] Bite problems
Horses may also experience an overbite/brachygnathism (parrot mouth), or an underbite/prognathism (sow mouth, monkey mouth). These may affect how the incisors wear. In severe cases, the horse's ability to graze may be affected.
The curvature of the incisors may also vary from the normal, straight bite. The curvature may be dorsal (upper incisors grow faster than lower), or ventral (lower incisors grow faster than upper). These curvatures may be the result of a chewing pattern, or due to retained deciduous teeth. The curvature may also be diagonal, stemming from a wear pattern of or pain in the cheek teeth (rather than the incisors), which causes the horse to chew in one direction over the other.
[edit] Other dental problems
Other common problems include abcessed, loose, infected, or cracked teeth, retained decisuous teeth, and plaque build up. Wolf teeth may also cause problems, and are many times removed, as are retained caps.
[edit] Signs of possible dental problems
- Reluctance to eat, does not finish food, or eats slowly
- Dull coat, weight loss, and loss of condition
- Quidding (horse drops partially chewed food while chewing), or chewing with the mouth open
- Turning of head to the side while chewing
- Excessive salivation while eating, blood in saliva
- Foul smell from mouth or nose
- Draining of abcess from the jaw
- Discharge from one nostril
- Undigested feed in manure
- Colic
- Excessive salivation
- Facial swelling
Additionally, many problems under saddle can be tooth-related, such as:
- head tossing
- difficulty in picking up the canter or in performing flying changes
- tilting of the head while riding or difficulty in bending
- refusal to collect
- bucking
- difficulty in getting the horse "on-the-bit" (especially if the horse tends to go behind the bit)
- gaping the mouth
For many performance-related problems, it is often best to check the teeth to rule out that factor.
[edit] Prevention of dental problems
To help prevent dental problems, it is recommended to get a horse's teeth checked by a veterinarian every 6 months. However, regular checks may be needed more often for individuals, especially if the horse is very young or very old. Additionally, the horse's teeth should be checked if it is having major performance problems or showing any of the above symptoms of a dental problem.
Many horses require floating (or rasping) of teeth once every 12 months, although this, too, is variable and dependant on the individual horse. Floating involves a veterinarian wearing down the surface of the teeth, usually to remove sharp points or to balance out the mouth. However, the veterinarian must be careful not to take off too much of the surface, or there will not be enough roughened area on the tooth to allow it to properly tear apart food. Additionally, too much work on a tooth can cause thermal damage (which could lead to having to extract the tooth), or expose the sensitive interior tooth.
[edit] Material to be Merged from Horse article
An adult female horse usually has 36-38 teeth. An adult male horse usually has 40-42 teeth. By the time a horse has reached the age of five they are considered to have a full mouth (all of their permanent teeth are present).
All adult horses have 12 permanent incisors, six are attached to the maxillary bone and the remaining six are attached to the mandible. The four incisors that are in the center are called the central incisors. The four incisors that are next to the central incisors are called intermediate or lateral incisors. The four incisors that are located on the ends of the incisors are the corner incisors. All male horses have four canines. The canines (tushes) are located directly behind the incisors. Occasionally a mare will show underdeveloped canines but it is uncommon. All horses have have 12 molars that are located at the back of the maxillary bone and the mandible. Horses also have 12 pre-molars which are located in front of the molars. Occasionally horses will have two extra small teeth that are located on the upper jaw in front of the premolars. These two teeth are called wolf teeth. Wolf teeth are actually the first pre-molars so most horses only have the 2nd, 3rd, and 4th premolars. Wolf teeth are usually removed because they interfere with the bit.
Most foals are born without teeth. The teeth appear at different intervals of the horses life. Incisors and pre-molars appear first as deciduous (baby) teeth that later shed and grow in as permanent. Molars and canines only appear as permanent.
Deciduous teeth Central incisors: Birth to two weeks of age Intermediate incisors: 4-6 weeks of age Corner incisors: 6-9 months of age 2nd pre-molars: About two weeks of age 3rd pre-molars: About two weeks of age 4th pre-molars: About two weeks of age Permanent Teeth Central incisors: 2 1/2 years of age Intermediate incisors: 3 1/2 years of age Corner incisors: 4 1/2 years of age 1st pre-molars(wolf teeth): 5-6 months 2nd pre-molars: 2 1/2 years 3rd pre-molars: 3 years 4th pre-molars: 4 years 1st molars: 9-12 months 2nd molars: 2 years 3rd molars: 3 1/2-4 years
Horses have indentions on the bottom of their incisors called cups that are the result of wear on their teeth. Age can be judged by looking at the size of the cups, the smaller the cups the older the horse. Eventually all the cups will disappear. This generally occurs when the horse is at the age of 12 years. The cups are replaced by dental stars. Occasionally the cups are retained, when this is happens the cup is now called a cap.
Another method of telling the age of a horse is by looking at galvayne's groove. Galvayne's groove is a line that appears a on the corner incisors of the maxillary bone when the horse reaches the age of 10 years. By the time the horse has reached 15 years the line has extended to the middle of the tooth. At the age of 20 years the line is at the bottom of the tooth. At the age of 25 years the line is once again half way up the tooth and disappears completely when the horse reaches the age of 30.
Age can also be determined by the shape of the teeth. A younger horse will have smaller teeth in a triangular shape. Older horses have long rectangular teeth. Older horses also have darker teeth. The angle at which the bottom and top incisors meet is also a good indication of age. The smaller the angle the older the horse.
[edit] References
- The Household Cyclopedia of General Information, published in 1881.
- Illustrated Atlas of Clinical Equine Anatomy and Common Disorders of the Horse, Vol. II. Riegel, Ronald J., and Susan E. Hakola. Equistar Publications, Limited. Copyright 1999.
- Equus. "Healthy Teeth, Healthy Horse." November 2006, pp 31-39.
