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www.equisearch.com/horses_care/health/dentistry/eqteeth2503/
Judging Horse Age from Teeth
Just how old is that horse? If you think the truth can always be found in his mouth, you may have swallowed an old horse-trader's line.
By Karen Smith
How can you tell if that horse you're examining is in his prime or over the hill? You could try pinching his skin, as Arab horsemen did. You could feel his jawbone, judge the distance between his ribs or look for a hollow above each eye. The body equine reveals its age in many ways: An older horse's skin is less pliable and "drier" than that of a younger horse, his jawbone is thinner and sharper, his ribs are spaced farther apart and his eyes sit deeper in their sockets. But none of these "tests" offers anything approaching the reliability of the one you're most likely to use: aging a horse by the appearance of his front teeth. Only registration papers recording the actual birth year provide a more consistently accurate indicator of a horse's age. Still, that doesn't mean that teeth are always truthful.
The method itself is ancient. Chinese drawings from as early as 700 B.C. show men looking in horses' mouths to determine the animals' ages. Common parlance still makes reference to the custom: Everyone knows it's impolite to "look a gift horse in the mouth." The practice dates back to a 19th-century Australian horse trainer and master of self-promotion, Sydney Galvayne, whose name is still associated with a telltale groove that appears on older horses' teeth. Illustrations of age-related changes in equine incisors based on Galvayne's system continue to appear in veterinary and horse-care texts. Only recently has research revealed that this technique--like any other long-held belief--has its exceptions and limitations.
Within the past four years, studies of age-related dental changes carried out in Britain and Belgium have confirmed what many suspected: Teeth do lie about age. One study demonstrated that even professionals who frequently examine horses' mouths can make honest mistakes in judging age based on the shape, coloration and configuration of the upper and lower incisors. In some cases, the experts were off by as much as seven or eight years. Other studies linked exceptions to the usual rules of dentition with breed and individual variations, or with diet and management practices.
In most horse-related transactions, age matters: A 12-year-old is a better investment as a broodmare than a 20-year-old; a four-year-old with lumpy ankles may have a shorter athletic life than a 10-year-old with similar enlargements; a two-year-old often requires different handling than a three-year-old; a selling price that's right on the mark for a seven-year-old is out of the ballpark for a 17-year-old. When legitimate documentation of a horse's birth date settles the critical question of age once and for all, the condition of his incisors is purely a matter of health care and management. But for the hordes of unregistered or otherwise paperless horses, and for the small number of horses offered or represented fraudulently, dentition remains an indispensable--though somewhat flawed--tool in establishing age. So the next time you find yourself looking a horse in the mouth to determine his age, be cautious before you pronounce him young and robust or elderly and infirm. You could be reading the indicators absolutely accurately--or, like the experts in the studies, you could be fooled by the testimony of the teeth.
Galvayne's legacy
Several British publications in the 19th century, including one as early as 1818, dealt with the subject of aging horses by their teeth. But it wasn't until Sydney Galvayne traveled throughout Europe in the 1880s, making a living by aging horses at sales and selling his secret to others, that the practice gained wide currency.
Galvayne claimed that he could tell the exact age of any horse brought to him. His book, Horse Dentition: Showing How to Tell Exactly the Age of a Horse up to Thirty Years, published in Glasgow around 1885, cites his numerous triumphs in the face of public skepticism. This account of a demonstration at a London riding school is typical:
The next animal was a bay mare. "Thirteen years," said I.
"Correct," said the owner, "but how do you do it?"
"You pay my fee, and you will know all about it," was my reply.
They then produced a gray. "Three years older than the last one," I quietly observed. "Sixteen years old."
"Right again, but how the deuce do you do it?" was the owner's remark.
I replied, "It's quite easy when you know how."
Galvayne's confident explication of age-linked changes in equine dentition and his claim of infallibility for his method caused considerable anxiety among crooked horse dealers. These shady characters soon developed fraudulent means for outwitting buyers who had read Galvayne's treatise. One such deception, called "bishoping" (after a well-known practitioner of the art), involved drilling new cups in aged incisors, then burning or dying these artificial infundibulums to resemble the dark cups found in more youthful mouths. At the other extreme, a too-young horse might have his baby teeth pulled to make him look six months to a year older.
In establishing his reputation, Galvayne had the advantage of dealing with a large population of horses kept under similar environmental and management conditions. The teeth of horses kept stabled and fed the same kinds of feed are apt to wear in consistent patterns. Soon widely accepted in Europe, Galvayne's system went on to become the basis for aging techniques taught in veterinary colleges around the world. His ideas are still found in a standard veterinary reference, The Official Guide to Determining the Age of a Horse, published in 1966 by the American Association of Equine Practitioners. The book is illustrated with photographs of teeth that match Galvayne's descriptions, but because the examples came from slaughterhouse skulls, there is no way of corroborating that the dental configurations are from horses who actually fit the ages specified.
Quantifying the evidence
Though veterinarians and other professionals grumbled over the years that Galvayne's aging formulas didn't seem to apply 100 percent to all horses, anecdotal objections did little to shake the faith most horsemen had in the technique. Then, in 1994, J.P. Walmsley, a British veterinarian, examined the teeth of a number of registered Thoroughbred horses between five and seven years of age and discovered a greater deviation from Galvayne's dental patterns than he had expected. For example, some of the five-year-olds had the teeth of a four-year-old, while others had mouths that would pass for eight.
The following year, six British researchers did another dental study, in which a number of experienced equine practitioners were asked to age horses--all registered and thus of known age--on the basis of their teeth alone. Results showed that with immature horses (age five and under), dental growth patterns differed enough from the expected to cause the experts to err in their estimates by as much as two years and nine months. Mature horses between five and 10 years of age were even more likely to be misjudged: Eight- and 10-year-olds were estimated by some experienced clinicians to be between 13 and 15; one six-year-old was judged by one veterinarian to be 12; two eight-year-olds were pegged at 15 by several veterinarians. Some much older horses, on the other hand, passed for mere youths: A 17-year-old was judged to be nine by one practitioner, and a 15-year-old was aged as seven by another.
One reason for the uncertainty in aging came to light in 1996, when three Belgian researchers examined the teeth of 570 horses representing several different types of horses--Arabians, Belgian draft horses and trotters. All were registered and of known ages, ranging from two to 25 years. The researchers found that the rate of dental wear was markedly different for each of the breeds--slower in Arabs, faster in the draft horses, somewhere in between in the trotters. Tooth composition and enamel hardness, both heritable traits, made the horses "age" at different rates. The study concluded that accurate aging by dentition has to be based on breed-specific guidelines.
The perils of prediction
Jack Easley, DVM, an equine practitioner in Shelbyville, Kentucky, who writes and lectures widely on equine dentistry, agrees that aging horses using Galvayne's formula is, at best, an educated guess and hardly the exact science that we have been led to believe it is.
"Horsemen of all types, veterinarians included, have perpetuated these theories, generation after generation, just because it was the way it was always done and it was what they were taught in school," Easley says. "You can certainly estimate whether the horse is within a certain age range by looking at his teeth, but in general, aging horses by studying their incisors is difficult and inaccurate." He believes that veterinarians and horsemen should take the recent research as an opportunity to reassess established practices.
Breed differences, such as those outlined in the Belgian study, are but one reason for the inaccuracies, Easley says. Individual rates of tooth emergence and wear account for other aging errors. The sequence of dental maturation takes horses from toothlessness at birth to a complete set of 36 full-size permanent teeth by age five--give or take some months. At predictable intervals, starting at day six, 24 temporary "milk" teeth erupt from the gums and are later shed, to be replaced by larger, more durable permanent teeth. (Because only geldings and stallions usually grow canine teeth--also called "tushes"--and both sexes may display the vestigial premolars known as "wolf teeth," the count of permanent teeth ranges between 36 and 42.)
When a horseman pulls back the lips of an immature animal and examines the incisors, he's checking the number of temporary and permanent teeth in the lineup as an indication of the youngster's age. But just as with human children, immature horses produce and shed milk teeth and acquire permanent replacements following roughly, but not precisely, the same schedule. Unlike human teeth, which stop growing once fully emerged, equine permanent teeth continue to erupt throughout the horse's life: As chewing wears away the surface tooth, new tooth material emerges from beneath the gum to replace it.
Easley also believes that the influence of management factors on the wear patterns of horse teeth has been overlooked in standard aging guides. Horses on pasture, for example, are constantly using their incisors to crop off grasses. The abrasiveness of forage varies with the amount of silicates (silica-based minerals) it contains, and grazers' incisors wear faster or slower depending upon forage type and the amount of their grazing. Additionally, horses who live in areas with sandy soil may wear their incisors more rapidly and give the appearance of being older than horses of the same chronological age who live on other soils.
Stall-kept horses, who use their front teeth primarily to pull hay from a net or rack, usually show less wear of the incisors than pastured horses. Feeding from a hayrack rather than from the ground also contributes to a more youthful mouth, Easley says, because the horse does not lower his head and stretch his neck when eating. This means that the normal change of the incisors' profile angle to a more forward slant is slowed.
In horses who suffer from abnormality in the way their teeth come together (malocclusion) or deformities such as overbite ("parrot mouth"), corrective dental care can play havoc with aging techniques by filing away all of the markings associated with age. But if malocclusions, broken teeth or other dental abnormalities are left untended, they produce irregular wear that can also confuse aging: For instance, a horse may give the appearance of being six years old on one side of his mouth and nine on the other. Mineral deficiencies are another cause of abnormal patterns in the teeth and can lead to errors in aging. Finally, horses who crib or run their teeth along stall bars may smooth the normal pattern of their incisors prematurely, making themselves appear older than they really are.
For almost a century, Galvayne's system of matching dental features to specific ages provided experts with a measure of certainty. We now know that this system is more of a guideline than a blueprint. Discovering that the master plan is inaccurate, even by a few degrees, can cause the builder-or the horseman--some unease. But it doesn't mean that the plan must be discarded. After all, it is not really surprising that individual horses grow, shed and replace their teeth on varying schedules, or that tooth wear varies among horses, depending on breed and environment. As long as you make allowances for some dental "dishonesty" when you look to a horse's mouth for an accounting of his years, you'll come away with some useful information. "This is the only way we have of aging horses," says Easley, "and while it may not be a very accurate method, it can still usually tell us if a horse is young, middle-aged or old, and it is still a valid thing to do."
Charting dental change
The permanent teeth of horses are called hypsodont, meaning that they have short roots (about three-quarters of an inch) and long crowns (as much as 41/2 inches in unworn teeth). Contained mostly within the gums at first, the crowns erupt at a rate of about one-eighth inch each year. This is enough to accommodate average wear and allow the upper and lower incisors to maintain contact--despite a lifetime of nipping and chewing--unless the lifetime exceeds 30 years, in which case the horse can actually use up his teeth. Sydney Galvayne based his famous aging system on the effect ordinary wear has in exposing successive levels of incisor material in horses after age five (the age when a horse has all his permanent teeth). The following alterations in appearance are the key indicators of increasing age.
The cement-lined enamel cup (infundibulum) on the biting (occiusal) surface of each incisor wears away in early maturity. The concave cups disappear on the central lower incisors at about age six, on the intermediate incisors at age seven, and on the corner incisors at age eight. Because the cups on the upper incisors are deeper, they take longer to disappear, but they are generally gone by the time a horse is 10 or 11. After the bottom of the back edge of the cup disappears (about age 15), the surface of each incisor is marked by a small, round enamel spot.
Yellow-brown dental stars appear between ages eight and 10, as the upper portion of the tooth is worn away. They are actually the pulp cavity, which has been filled in with secondary dentin as the tooth has matured. These stars" start out as dark lines in the center of the tooth, then change to more star-like ovals at about age 13, and finally become round at about age 15. In elderly horses, the occlusal surface is worn smooth and patternless.
As the horse ages, the shape of the incisors' occlusal surfaces alters from narrow oval to roundish to triangular, eventually becoming longer from front to back than side to side.
The profile of the upper and lower arcades progresses from nearly upright in young horses to a forward slant in the elderly.
Galvayne relied on two other dental features to determine the age of mature horses. One is a hook that is supposed to appear on the outer edge of each upper corner incisor at seven, disappear at age eight and return age 11. The second is the yellow-brown groove called Galvayne's groove, said to appear at the gum line of the upper corner incisor at age 10 and lengthen as the horse ages, spanning the entire tooth by age 20, then leaving the gum line and advancing toward the bottom of the tooth until it wears out by age 30. A 1996 Belgian research study found that hooks apparent in only two of the 15 seven-year-old horses, and in both cases they appeared one side of the mouth only. As for the famous groove, Belgian researchers found no consistency in the size, length or even existence of the trait in horses of the specified ages.
Common dental terms
arcade -- a row of teeth on one side of a horse's jaw.
bars -- the toothless spaces between the incisors and the cheek teeth. canine-the nonchewing teeth seen in males (and sometimes females) at the front of the bars area.
cement -- the comparatively soft material that (1) covers the outside of a tooth, (2) connects the tooth to the jawbone beneath the gum's surface and (3) fills the inside of the incisor cups.
cheek teeth -- taken together, the 12 premolars and 12 molars that are responsible for masticating food in a circular, grinding motion.
crown -- the part of the tooth that emerges above the gums.
cup (infundibulum) -- the dark-brown to black cement-lined "crater" in the biting surface of each permanent incisor tooth that is worn away by the time the horse is eight years old, leaving a flat mark called an enamel spot.
dental star -- the brownish dentin, exposed by wear, that appears between the enamel spot and the front of each permanent incisor, starting with the central incisors about age eight. Initially a straight line across the tooth, the dental star curves with age, and eventually becomes round and dark brown on all incisors.
dentin -- the bonelike material that makes up the greater part of the tooth below the surface layer of enamel. enamel-the calcium-rich substance that forms a thin layer over the incisor teeth and is complexly folded into the horse's molar teeth; the hardest tissue of the body.
enamel spot -- the white enamel tooth cup that is left visible when cement has worn away.
hypsodont -- teeth that have long crowns and short roots, in contrast to the crowned "brachyodont" teeth typical of other grazers, such as cows and deer
hook -- a sharp projection on the surface of a tooth, often caused I uneven wear.
incisors -- front teeth used for cutting rather than grinding, Numbering six on the top and six on the bottom in adult horses, these are further distinguished in the central (first), intermediate (second) and corner (third) upper and lower incisors.
malocclusion -- abnormality in alignment of upper and lower teeth
milk teeth -- deciduous, or baby teeth; young horses have 24.
molars -- the 12 nondeciduous cheek teeth, three at the back of each arcade.
occlusal surface -- the biting of the tooth.
permanent teeth -- the long, large teeth that replace the original milk teeth by the time the horse is five years old
premolars -- the first three cheek teeth in each arcade, located directly behind the bars. They are replaced by permanent premolars between age 21/2 and four
profile -- the slant of the incisors. Profile angle changes from fairly upright in young horses to extremely slanted in old horses
pulp -- the living tissue at the heart of a tooth, including the nerves and the blood vessels. As the pulp recedes over the years, it leaves behind stained dentin, which steadily emerges as the dental star.
EQUUS thanks Jack Easley, DVM, for his help in the preparation of this article. Easley, a 1976 graduate of theTuskegee University School of Veterinary Medicine, with postgraduate work at Oklahoma State University and Kansas State University, specializes in equine reproduction, surgery and dentistry at his practice in central Kentucky. He has published and lectured on equine dentistry and oral disease for more than 20 years, and presented equine dental short courses to both veterinarians and lay groups in the United States, Canada, Europe and Australia.
This article first appeared in the September 1998 issue of EQUUS magazine.
www.equisearch.com/horses_care/health/dentistry/eqteeth2503/
Judging Horse Age from Teeth
Just how old is that horse? If you think the truth can always be found in his mouth, you may have swallowed an old horse-trader's line.
By Karen Smith
How can you tell if that horse you're examining is in his prime or over the hill? You could try pinching his skin, as Arab horsemen did. You could feel his jawbone, judge the distance between his ribs or look for a hollow above each eye. The body equine reveals its age in many ways: An older horse's skin is less pliable and "drier" than that of a younger horse, his jawbone is thinner and sharper, his ribs are spaced farther apart and his eyes sit deeper in their sockets. But none of these "tests" offers anything approaching the reliability of the one you're most likely to use: aging a horse by the appearance of his front teeth. Only registration papers recording the actual birth year provide a more consistently accurate indicator of a horse's age. Still, that doesn't mean that teeth are always truthful.
The method itself is ancient. Chinese drawings from as early as 700 B.C. show men looking in horses' mouths to determine the animals' ages. Common parlance still makes reference to the custom: Everyone knows it's impolite to "look a gift horse in the mouth." The practice dates back to a 19th-century Australian horse trainer and master of self-promotion, Sydney Galvayne, whose name is still associated with a telltale groove that appears on older horses' teeth. Illustrations of age-related changes in equine incisors based on Galvayne's system continue to appear in veterinary and horse-care texts. Only recently has research revealed that this technique--like any other long-held belief--has its exceptions and limitations.
Within the past four years, studies of age-related dental changes carried out in Britain and Belgium have confirmed what many suspected: Teeth do lie about age. One study demonstrated that even professionals who frequently examine horses' mouths can make honest mistakes in judging age based on the shape, coloration and configuration of the upper and lower incisors. In some cases, the experts were off by as much as seven or eight years. Other studies linked exceptions to the usual rules of dentition with breed and individual variations, or with diet and management practices.
In most horse-related transactions, age matters: A 12-year-old is a better investment as a broodmare than a 20-year-old; a four-year-old with lumpy ankles may have a shorter athletic life than a 10-year-old with similar enlargements; a two-year-old often requires different handling than a three-year-old; a selling price that's right on the mark for a seven-year-old is out of the ballpark for a 17-year-old. When legitimate documentation of a horse's birth date settles the critical question of age once and for all, the condition of his incisors is purely a matter of health care and management. But for the hordes of unregistered or otherwise paperless horses, and for the small number of horses offered or represented fraudulently, dentition remains an indispensable--though somewhat flawed--tool in establishing age. So the next time you find yourself looking a horse in the mouth to determine his age, be cautious before you pronounce him young and robust or elderly and infirm. You could be reading the indicators absolutely accurately--or, like the experts in the studies, you could be fooled by the testimony of the teeth.
Galvayne's legacy
Several British publications in the 19th century, including one as early as 1818, dealt with the subject of aging horses by their teeth. But it wasn't until Sydney Galvayne traveled throughout Europe in the 1880s, making a living by aging horses at sales and selling his secret to others, that the practice gained wide currency.
Galvayne claimed that he could tell the exact age of any horse brought to him. His book, Horse Dentition: Showing How to Tell Exactly the Age of a Horse up to Thirty Years, published in Glasgow around 1885, cites his numerous triumphs in the face of public skepticism. This account of a demonstration at a London riding school is typical:
The next animal was a bay mare. "Thirteen years," said I.
"Correct," said the owner, "but how do you do it?"
"You pay my fee, and you will know all about it," was my reply.
They then produced a gray. "Three years older than the last one," I quietly observed. "Sixteen years old."
"Right again, but how the deuce do you do it?" was the owner's remark.
I replied, "It's quite easy when you know how."
Galvayne's confident explication of age-linked changes in equine dentition and his claim of infallibility for his method caused considerable anxiety among crooked horse dealers. These shady characters soon developed fraudulent means for outwitting buyers who had read Galvayne's treatise. One such deception, called "bishoping" (after a well-known practitioner of the art), involved drilling new cups in aged incisors, then burning or dying these artificial infundibulums to resemble the dark cups found in more youthful mouths. At the other extreme, a too-young horse might have his baby teeth pulled to make him look six months to a year older.
In establishing his reputation, Galvayne had the advantage of dealing with a large population of horses kept under similar environmental and management conditions. The teeth of horses kept stabled and fed the same kinds of feed are apt to wear in consistent patterns. Soon widely accepted in Europe, Galvayne's system went on to become the basis for aging techniques taught in veterinary colleges around the world. His ideas are still found in a standard veterinary reference, The Official Guide to Determining the Age of a Horse, published in 1966 by the American Association of Equine Practitioners. The book is illustrated with photographs of teeth that match Galvayne's descriptions, but because the examples came from slaughterhouse skulls, there is no way of corroborating that the dental configurations are from horses who actually fit the ages specified.
Quantifying the evidence
Though veterinarians and other professionals grumbled over the years that Galvayne's aging formulas didn't seem to apply 100 percent to all horses, anecdotal objections did little to shake the faith most horsemen had in the technique. Then, in 1994, J.P. Walmsley, a British veterinarian, examined the teeth of a number of registered Thoroughbred horses between five and seven years of age and discovered a greater deviation from Galvayne's dental patterns than he had expected. For example, some of the five-year-olds had the teeth of a four-year-old, while others had mouths that would pass for eight.
The following year, six British researchers did another dental study, in which a number of experienced equine practitioners were asked to age horses--all registered and thus of known age--on the basis of their teeth alone. Results showed that with immature horses (age five and under), dental growth patterns differed enough from the expected to cause the experts to err in their estimates by as much as two years and nine months. Mature horses between five and 10 years of age were even more likely to be misjudged: Eight- and 10-year-olds were estimated by some experienced clinicians to be between 13 and 15; one six-year-old was judged by one veterinarian to be 12; two eight-year-olds were pegged at 15 by several veterinarians. Some much older horses, on the other hand, passed for mere youths: A 17-year-old was judged to be nine by one practitioner, and a 15-year-old was aged as seven by another.
One reason for the uncertainty in aging came to light in 1996, when three Belgian researchers examined the teeth of 570 horses representing several different types of horses--Arabians, Belgian draft horses and trotters. All were registered and of known ages, ranging from two to 25 years. The researchers found that the rate of dental wear was markedly different for each of the breeds--slower in Arabs, faster in the draft horses, somewhere in between in the trotters. Tooth composition and enamel hardness, both heritable traits, made the horses "age" at different rates. The study concluded that accurate aging by dentition has to be based on breed-specific guidelines.
The perils of prediction
Jack Easley, DVM, an equine practitioner in Shelbyville, Kentucky, who writes and lectures widely on equine dentistry, agrees that aging horses using Galvayne's formula is, at best, an educated guess and hardly the exact science that we have been led to believe it is.
"Horsemen of all types, veterinarians included, have perpetuated these theories, generation after generation, just because it was the way it was always done and it was what they were taught in school," Easley says. "You can certainly estimate whether the horse is within a certain age range by looking at his teeth, but in general, aging horses by studying their incisors is difficult and inaccurate." He believes that veterinarians and horsemen should take the recent research as an opportunity to reassess established practices.
Breed differences, such as those outlined in the Belgian study, are but one reason for the inaccuracies, Easley says. Individual rates of tooth emergence and wear account for other aging errors. The sequence of dental maturation takes horses from toothlessness at birth to a complete set of 36 full-size permanent teeth by age five--give or take some months. At predictable intervals, starting at day six, 24 temporary "milk" teeth erupt from the gums and are later shed, to be replaced by larger, more durable permanent teeth. (Because only geldings and stallions usually grow canine teeth--also called "tushes"--and both sexes may display the vestigial premolars known as "wolf teeth," the count of permanent teeth ranges between 36 and 42.)
When a horseman pulls back the lips of an immature animal and examines the incisors, he's checking the number of temporary and permanent teeth in the lineup as an indication of the youngster's age. But just as with human children, immature horses produce and shed milk teeth and acquire permanent replacements following roughly, but not precisely, the same schedule. Unlike human teeth, which stop growing once fully emerged, equine permanent teeth continue to erupt throughout the horse's life: As chewing wears away the surface tooth, new tooth material emerges from beneath the gum to replace it.
Easley also believes that the influence of management factors on the wear patterns of horse teeth has been overlooked in standard aging guides. Horses on pasture, for example, are constantly using their incisors to crop off grasses. The abrasiveness of forage varies with the amount of silicates (silica-based minerals) it contains, and grazers' incisors wear faster or slower depending upon forage type and the amount of their grazing. Additionally, horses who live in areas with sandy soil may wear their incisors more rapidly and give the appearance of being older than horses of the same chronological age who live on other soils.
Stall-kept horses, who use their front teeth primarily to pull hay from a net or rack, usually show less wear of the incisors than pastured horses. Feeding from a hayrack rather than from the ground also contributes to a more youthful mouth, Easley says, because the horse does not lower his head and stretch his neck when eating. This means that the normal change of the incisors' profile angle to a more forward slant is slowed.
In horses who suffer from abnormality in the way their teeth come together (malocclusion) or deformities such as overbite ("parrot mouth"), corrective dental care can play havoc with aging techniques by filing away all of the markings associated with age. But if malocclusions, broken teeth or other dental abnormalities are left untended, they produce irregular wear that can also confuse aging: For instance, a horse may give the appearance of being six years old on one side of his mouth and nine on the other. Mineral deficiencies are another cause of abnormal patterns in the teeth and can lead to errors in aging. Finally, horses who crib or run their teeth along stall bars may smooth the normal pattern of their incisors prematurely, making themselves appear older than they really are.
For almost a century, Galvayne's system of matching dental features to specific ages provided experts with a measure of certainty. We now know that this system is more of a guideline than a blueprint. Discovering that the master plan is inaccurate, even by a few degrees, can cause the builder-or the horseman--some unease. But it doesn't mean that the plan must be discarded. After all, it is not really surprising that individual horses grow, shed and replace their teeth on varying schedules, or that tooth wear varies among horses, depending on breed and environment. As long as you make allowances for some dental "dishonesty" when you look to a horse's mouth for an accounting of his years, you'll come away with some useful information. "This is the only way we have of aging horses," says Easley, "and while it may not be a very accurate method, it can still usually tell us if a horse is young, middle-aged or old, and it is still a valid thing to do."
Charting dental change
The permanent teeth of horses are called hypsodont, meaning that they have short roots (about three-quarters of an inch) and long crowns (as much as 41/2 inches in unworn teeth). Contained mostly within the gums at first, the crowns erupt at a rate of about one-eighth inch each year. This is enough to accommodate average wear and allow the upper and lower incisors to maintain contact--despite a lifetime of nipping and chewing--unless the lifetime exceeds 30 years, in which case the horse can actually use up his teeth. Sydney Galvayne based his famous aging system on the effect ordinary wear has in exposing successive levels of incisor material in horses after age five (the age when a horse has all his permanent teeth). The following alterations in appearance are the key indicators of increasing age.
The cement-lined enamel cup (infundibulum) on the biting (occiusal) surface of each incisor wears away in early maturity. The concave cups disappear on the central lower incisors at about age six, on the intermediate incisors at age seven, and on the corner incisors at age eight. Because the cups on the upper incisors are deeper, they take longer to disappear, but they are generally gone by the time a horse is 10 or 11. After the bottom of the back edge of the cup disappears (about age 15), the surface of each incisor is marked by a small, round enamel spot.
Yellow-brown dental stars appear between ages eight and 10, as the upper portion of the tooth is worn away. They are actually the pulp cavity, which has been filled in with secondary dentin as the tooth has matured. These stars" start out as dark lines in the center of the tooth, then change to more star-like ovals at about age 13, and finally become round at about age 15. In elderly horses, the occlusal surface is worn smooth and patternless.
As the horse ages, the shape of the incisors' occlusal surfaces alters from narrow oval to roundish to triangular, eventually becoming longer from front to back than side to side.
The profile of the upper and lower arcades progresses from nearly upright in young horses to a forward slant in the elderly.
Galvayne relied on two other dental features to determine the age of mature horses. One is a hook that is supposed to appear on the outer edge of each upper corner incisor at seven, disappear at age eight and return age 11. The second is the yellow-brown groove called Galvayne's groove, said to appear at the gum line of the upper corner incisor at age 10 and lengthen as the horse ages, spanning the entire tooth by age 20, then leaving the gum line and advancing toward the bottom of the tooth until it wears out by age 30. A 1996 Belgian research study found that hooks apparent in only two of the 15 seven-year-old horses, and in both cases they appeared one side of the mouth only. As for the famous groove, Belgian researchers found no consistency in the size, length or even existence of the trait in horses of the specified ages.
Common dental terms
arcade -- a row of teeth on one side of a horse's jaw.
bars -- the toothless spaces between the incisors and the cheek teeth. canine-the nonchewing teeth seen in males (and sometimes females) at the front of the bars area.
cement -- the comparatively soft material that (1) covers the outside of a tooth, (2) connects the tooth to the jawbone beneath the gum's surface and (3) fills the inside of the incisor cups.
cheek teeth -- taken together, the 12 premolars and 12 molars that are responsible for masticating food in a circular, grinding motion.
crown -- the part of the tooth that emerges above the gums.
cup (infundibulum) -- the dark-brown to black cement-lined "crater" in the biting surface of each permanent incisor tooth that is worn away by the time the horse is eight years old, leaving a flat mark called an enamel spot.
dental star -- the brownish dentin, exposed by wear, that appears between the enamel spot and the front of each permanent incisor, starting with the central incisors about age eight. Initially a straight line across the tooth, the dental star curves with age, and eventually becomes round and dark brown on all incisors.
dentin -- the bonelike material that makes up the greater part of the tooth below the surface layer of enamel. enamel-the calcium-rich substance that forms a thin layer over the incisor teeth and is complexly folded into the horse's molar teeth; the hardest tissue of the body.
enamel spot -- the white enamel tooth cup that is left visible when cement has worn away.
hypsodont -- teeth that have long crowns and short roots, in contrast to the crowned "brachyodont" teeth typical of other grazers, such as cows and deer
hook -- a sharp projection on the surface of a tooth, often caused I uneven wear.
incisors -- front teeth used for cutting rather than grinding, Numbering six on the top and six on the bottom in adult horses, these are further distinguished in the central (first), intermediate (second) and corner (third) upper and lower incisors.
malocclusion -- abnormality in alignment of upper and lower teeth
milk teeth -- deciduous, or baby teeth; young horses have 24.
molars -- the 12 nondeciduous cheek teeth, three at the back of each arcade.
occlusal surface -- the biting of the tooth.
permanent teeth -- the long, large teeth that replace the original milk teeth by the time the horse is five years old
premolars -- the first three cheek teeth in each arcade, located directly behind the bars. They are replaced by permanent premolars between age 21/2 and four
profile -- the slant of the incisors. Profile angle changes from fairly upright in young horses to extremely slanted in old horses
pulp -- the living tissue at the heart of a tooth, including the nerves and the blood vessels. As the pulp recedes over the years, it leaves behind stained dentin, which steadily emerges as the dental star.
EQUUS thanks Jack Easley, DVM, for his help in the preparation of this article. Easley, a 1976 graduate of theTuskegee University School of Veterinary Medicine, with postgraduate work at Oklahoma State University and Kansas State University, specializes in equine reproduction, surgery and dentistry at his practice in central Kentucky. He has published and lectured on equine dentistry and oral disease for more than 20 years, and presented equine dental short courses to both veterinarians and lay groups in the United States, Canada, Europe and Australia.
This article first appeared in the September 1998 issue of EQUUS magazine.