Chapter 9 Determining age, height, and weight of horses.
After completing this chapter, you should be able to:
* List the names used for different age groups of horses from birth to 3 years
* Discuss the importance of knowing the age of a horse
* Name four changes in teeth that are indicators of different ages
* Diagram a tooth to show the parts that change during the aging process
* Describe the changes horses' teeth exhibit during their lifetime
* List the temporary and permanent teeth of the horse and their approximate time of eruption
* List four abnormal tooth conditions
* Give four reasons that knowing the height and weight of a horse is important
* Tell how to determine the height of a horse in hands and inches
* Calculate the weight of a horse from the measurements of the heart girth and body length
angle of incidence
IMPORTANCE OF AGE
Young horses are referred to by their age. The young horse is called a foal until it is weaned. A male horse is referred to as a colt until it is 3 years old, and then it is called a stallion. A young female horse is called a filly until it reaches the age of 3, when it is referred to as a mare. Sometimes the term weanling is used for horses that are 6 months to 1 year of age. Horses 1 to 2 years old may be called yearlings, and horses 2 years of age may be called 2-year-olds.
A horse's condition and training are more important than its age. Prime age for a horse is about 7 to 9 years, but this is not necessarily the ideal age. Horses frequently are active into their late 20s if they get proper care.
Buyers can often purchase top-quality older horses at the same price or less than they would pay for younger horses of lesser quality. Although most older horses cannot perform as actively as they did when younger, they may have many years of useful service left.
Buyers should be ready to decide whether they prefer a younger horse or if an older one would do as well. This decision cannot be made until the buyer evaluates the individual horse. Finally, the age of the horse purchased depends on what the buyer can afford and what horses the buyer finds available.
Age is also important for competitive events. For racing or showing events, the foal's birth date is considered to be January 1, regardless of the actual month of birth during the year. So a foal born April 1, 2001, will be 10 years old on January 1, 2011. Individuals who race or show try to have foals born as near to January 1 as possible. This gives the horse the advantage of more growth than those born later in the year.
USING TEETH TO DETERMINE AGE
Of course, the best way to determine the age of a horse is from good records. A record of a horse's birth is required by breed registries. When a record of age does not exist, the teeth furnish the best estimation of the age of a horse.
The art of determining the age of horses by inspection of the teeth is an old one. It can be used with a considerable degree of accuracy in determining the age of young horses. The probability of error increases as age advances and becomes a guess after the horse reaches 10 to 14 years of age. Stabled animals tend to appear younger than they are, whereas those grazing sandy areas, such as range horses, appear relatively older because of wear on the teeth.
Age determination is made by a study of the 12 front teeth, called incisors. The two central pairs both above and below are called centrals (centers), pincers, or nippers. The four teeth adjacent to these two pairs are called intermediates, and the outer four teeth are designated as corners.
Canine teeth or "tusks" may appear midway between the incisors and molars at 4 or 5 years of age in the case of geldings or stallions, but seldom appear in mares. Adult horses have 24 molar teeth (Figure 9-1).
Four key changes in the teeth can be used to estimate the age of horses:
1. Occurrence of permanent teeth
2. Disappearance of cups
3. Angle of incidence
4. Shape of the surface of the teeth
Occurrence of Permanent Teeth
Horses have two sets of teeth, one temporary and one permanent. Temporary teeth may also be called baby or milk teeth. Temporary incisors tend to erupt in pairs at 8 days, 8 weeks, and 8 months of age.
A well-grown 2-year-old may be mistaken for an older horse unless permanent teeth can be accurately identified. Permanent teeth are larger, longer, darker in color, and do not have the well-defined neck joining root and gum that temporary teeth do.
The four center permanent teeth appear (two above and two below) as the animal approaches 3 years of age, the intermediates at 4, and the corners at 5. This constitutes a full mouth.
Disappearance of Cups
In the center of their surfaces, young permanent teeth have deep indentures referred to as cups. Cups are commonly used as reference points in determining age. Those in the upper teeth are deeper than the ones below, so they do not wear evenly with the surface or become smooth at the same rate. In general, the cups become smooth in the lower centers, intermediates, corners, upper centers, intermediates, and corners at 6, 7, 8, 9, 10, and 11 years of age, respectively. A smooth mouth theoretically appears at 11. A few horse owners ignore cups in the upper teeth and consider a 9-year-old horse smooth-mouthed. Although complete accuracy cannot be ensured from studying cups, this method is second in accuracy only to the appearance of permanent teeth in determining age.
[FIGURE 9-1 OMITTED]
As cups disappear, dental stars appear--first as narrow, yellow lines in front of the central enamel ring, then as dark circles near the center of the tooth in advanced age.
Angle of Incidence
The angle formed by the meeting of the upper and lower incisor teeth (profile view) affords an indication of age. This angle of incidence or "contact" changes from approximately 160 to 180 degrees in young horses, to less than a right angle as the incisors appear to slant forward and outward with aging. As the slant increases, the surfaces of the lower corner teeth do not wear clear to the back margin of the uppers, so that a dovetail, notch, or hook is formed on the upper corners at 7 years of age. It may disappear in a year or two, reappear around 12 to 15 years, and disappear again. The condition varies considerably between individuals, but most horses have a well-developed notch at 7.
Shape of the Surface of the Teeth
The teeth change substantially in shape during wear and aging. They appear broad and flat in young horses. They may be twice as wide (side to side) as they are deep (front to rear). This condition reverses itself in horses that reach or pass 20 years. From about 8 to 12 years, the back (inside) surfaces become oval, then triangular at about 15 years. Twenty-year-old teeth may be twice as deep from front to rear as they are wide (Figure 9-2).
[FIGURE 9-2 OMITTED]
STRUCTURE OF THE TOOTH
Being able to estimate the age of a horse by its teeth also requires an understanding of the structure of the tooth and different stages of wear. Figure 9-2 shows the structure of a tooth as viewed longitudinally and in cross section. As the horse ages and the tooth wears, different portions of the tooth become visible.
NUMBER AND TYPE OF TEETH
Table 9-1 summarizes the numbers, types, and appearance of teeth in horses.
Less than Two Weeks
Between birth and 2 weeks of age, the newborn has its first pair of incisors erupt. These are the central incisors. In profile, the mucous membrane of the gums will be a thin cover over the intermediate incisors. The temporary first, second, and third premolar should be present.
Four to Six Weeks
Between 4 and 6 weeks of age, eruption of the second set of incisors, the intermediates, occurs. The central incisors are in contact and coming into wear. The intermediates are not in contact, have no wear, and the cups are deep.
Six to Ten Months
The final set of temporary incisors, the corners, erupts between 6 and 10 months of age. The permanent first premolar (or wolf tooth) erupts. Not all horses have this wolf tooth. The dental surfaces of the centrals and intermediates start to show wear. The cup is shallower in the centrals than the intermediates because they have been in wear longer. The corners are not in contact with each other.
How Old Is Your Horse? This poem helped old-timers remember how to use the teeth to tell the age of a horse. To tell the age of any horse Inspect the lower jaw of course. Two middle nippers you'll behold Before the colt is two weeks old. Before six weeks two more will come; Twelve months the corners cut the gum. At two the middle nippers drop; At three the second pair can't stop. At four years old the side pair shows; At five a full new mouth he grows. Black spots will pass from view At six years from the middle two. The side two pairs at seven years, And eight will find the corners clear. The middle nipper, upper jaw, At nine the black spots will withdraw. At ten years old the sides are light; Eleven finds the corners white. As time goes on the horsemen know The oval teeth three-sided grow. They longer get, project before, 'Til twenty when we know no more! --Anonymous
All the temporary incisors are visible from the front. In profile, the upper and lower corner incisors are not in contact. The dental surfaces of the centrals show considerable wear. The dental star is seen usually in the centrals and intermediates as a dark or yellowish-brown transverse line in the dentin on the labial (the surface of the tooth closest to the gums) side of the infundibulum (the funnel-shaped inside of the tooth). The first molar should be present by 1 year.
The central and intermediate incisors are now quite free from the gum, especially the upper incisors. All pairs of the incisors should be in wear. The dental surface of the lower central incisors is smooth; the intermediates show decided wear; the corners show considerable wear. The dental star is clearly visible in the lower incisors. Eruption of the second molar occurs.
Two and One-Half Years
The first pair of permanent incisors erupt. The upper central incisors have not reached the level of the deciduous intermediates. The lower permanent central incisors have erupted through the gum, but most of the labial surface of the lower incisors is covered by mucous membrane. In profile, the intermediate and corner incisors show distinct necks. The dental surface shows the intermediates worn smooth and the corners with noticeable wear. The second permanent premolar erupts as well.
The first set of permanent incisors, the centrals, are now in wear. They are more solid in appearance, are larger and broader than the temporary teeth, and have vertical ridges and grooves. The dental table of the central incisors has a deep cup, and the borders are sharp. Eruption of the third premolar takes place.
Three and One-Half Years
The second pair of permanent incisors, the intermediates, erupt. The central incisors are well in wear. The intermediates are nearing contact. In profile, the gap between the upper and lower intermediates is visible. The dental surfaces show wear on the centrals. The intermediates are sharp since they have not made contact yet. The temporary corners are nearly smooth.
The first two sets of permanent incisors are now in wear. The jaws have acquired so much width that from the front, the corner temporary incisors are barely visible. Canines start to erupt. These may erupt as early as 31/2 years or as late as 5 years. The dental surfaces of the central incisors show wear, but the cups are deep. The intermediates are in wear, but sharp. The fourth premolar erupts as well as the third molar.
Four and One-Half Years
The last pair of incisors, the corners, erupt. Head on, the central and intermediate incisors are in contact. The permanent corners are visible, but they are not in contact. In profile, the upper and lower canines are erupting and are sharp. The dental surfaces have distinct cups in the centrals and intermediates, while the corners are sharp.
The permanent dentition is complete. All the incisors are in wear. The canines have erupted completely. The dental surfaces of the centrals and intermediates are wide transversely and show wear, but their cups are readily visible and completely encircled by the central enamel.
Dental surfaces of the lower centrals are usually smooth, and the shape is more oval. The central enamel is not as wide as it was at 5 years, and it is closer to the surface of the tooth closest to the tongue surface. The intermediates have distinct cups but otherwise resemble the centrals. The corners show wear. The canines have reached their full length and are in wear.
In profile, the dental surface of the lower corner incisor is narrower than that of the upper. This leads to a notch on the caudal corner of the upper incisor--the 7-year notch or hook. Dental surfaces of the lower central and intermediate incisors are smooth. Cups are no longer present. The lower corners retain their cups.
Lower dental surfaces are smooth, and all cups are gone in lower corners. The dental star appears in the lower central incisors, first as a dark yellow or yellow-brown transverse line in the dentin on the cheek side of the infundibulum of the permanent central incisor. The central and intermediate incisors are oval.
The 7-year hook has usually disappeared by 9 years. The distal end of Galvayne's groove may be visible at the margin of the gum on the upper corner incisors (Figure 9-3). The central incisors are round, while their central enamel is triangular. Their dental star is more distinct and narrower and near the center of the dental surfaces. The intermediate incisors are becoming round, while the corners are oval.
[FIGURE 9-3 OMITTED]
The angle of the teeth is more oblique. The distal end of Galvayne's groove should be visible on the upper corner of the upper incisor. Dental surfaces of the lower central and intermediate incisors are round, while the corner incisors are oval to round. The central enamel is triangular in the central incisors and close to the lingual border. The dental star is more distinct and near the center of the teeth. Galvayne's groove appears at the gum margin of the upper corner incisor at about 10 years of age, extends halfway down the tooth at 15 years, and reaches the table margin at 20. It then recedes and disappears at 30 years of age.
The hook on the upper corner incisor returns (it may not appear until 12 years, and it usually persists to 15 years). The angle of the jaw increases in obliquity. The central enamel of each lower incisor forms a small ring close to the lingual border. Dental stars are narrower transversely and near the center of the dental table.
Dental surfaces of all the lower incisors should be round. The central enamel is small and round, and it is disappearing from the centrals. The dental star is seen as a small yellow spot near the center of the dental surfaces.
Dental surfaces of the lower centrals may appear round or triangular. The central enamel in the lower incisors is small and round and, in many instances, disappearing. Dental stars are near the middle of the dental surfaces. The length of the teeth and the shape of the dental surfaces are the important markers for this age.
Galvayne's groove extends halfway down the labial (the surface of the tooth closest to the gums) surface of the upper corner incisors. The dental surfaces of the lower central incisors appear triangular. The intermediates are round to triangular and all lower incisors show a dark, distinct dental star.
Dental surfaces of the lower incisors are triangular. Dental stars are round and near the center of their respective teeth. Head on, the corner incisors are inclining slightly to the inside. In profile, the angle of the incisors is increasing.
Galvayne's groove extends down the entire length of the labial surface (the surface of the tooth closest to the gums) of the upper corner incisors. The upper corner incisors deviate distinctly toward the median plane. Deviation of the intermediates is not as marked. The dental table of the lower incisors may be compressed transversely and may be worn almost to the gum (Figure 9-4).
Abnormal Tooth Conditions
Several factors influence the wear and appearance of teeth: bite, cribbing, bishoping, and floating.
* Parrot mouth is a result of the upper and lower incisors not meeting because the lower jaw is too short. If it also affects the molars, then sharp points and hooks may form during wear. This condition is rather common and may seriously interfere with grazing (Figure 9-5).
* Monkey mouth is the opposite of parrot mouth and is seldom seen in horses.
* Cribbing is a habit common to stabled horses that damages incisors by chipping or breaking them.
* Bishoping is tampering with cups to make the horse appear younger than it is.
* Floating is filing high spots in molars to facilitate chewing. Molars should be checked regularly by veterinarians as the horse approaches midlife and should be kept floated as needed (Figure 9-6).
[FIGURE 9-4 OMITTED]
[FIGURE 9-5 OMITTED]
Since the molars can become razor sharp, one should avoid placing fingers in the horse's mouth.
OTHER INDICATORS OF AGE
The features of older horses are a little like those of older people. The sides of the face become more depressed, the poll more prominent, and the hollows above the eyes deeper. The backbone becomes more prominent and starts to sag, and the joints appear more angular. Around the temples, eyes, nostrils, and elsewhere, white hair appears.
Typical measurements such as height, weight, and girth are influenced by age. These measurements are also affected by breed, type, sex, and nutrition.
Height can influence price. Ponies are often cheaper because their use is limited. Horses are measured in hands. A hand is equal to 4 inches. With the horse on level ground, the point of measurement is the distance from the highest point of the withers to the ground. So, a horse measuring 60 inches is a 15-hand horse.
Height changes as a foal grows. Figure 9-7 shows how the height of Thoroughbred foals changes as they age.
[FIGURE 9-6 OMITTED]
[FIGURE 9-7 OMITTED]
Breed, type, and age determine the weight of a horse. Figure 9-8 graphically demonstrates how rapidly a horse increases in body weight as it matures. Knowing the weight of a horse is important for determining:
* Amount of feed needed
* Adequacy of a feeding program
* Potential health problems
* Optimal training and competing
* Maximal breeding efficiency
* Proper amount of medication
A University of Florida study found 88 percent of visual guesses on horses' weight resulted in underestimates. The best way is to use a truck scale: Weigh the trailer and horse together and then weigh the trailer unloaded. Weight tapes give only rough estimates. For those who cannot use the truck scale method, researchers developed the following formula, using heart girth and body length.
[FIGURE 9-8 OMITTED]
Measure the heart girth just behind the elbow, taking the reading right after the horse exhales. Measure body length from the point of the shoulder to the point of the buttocks in a straight line. Avoid using a cloth measuring tape because it may stretch. A metal carpenter's tape is accurate, but it is noisy and can spook a horse. A plastic-coated tape works best. If one is not available, use cord or string that has no stretch, and mark the spot with a pen. Then measure the cord with a carpenter's tape or yardstick.
Take the two measurements and multiply the heart girth (in inches) times itself. Then multiply that number by the body length in inches. Divide the total by 330 for the approximate weight in pounds.
For example, if the horse measures 75 inches around the heart girth, and body length is 64 inches:
heart girth x heart girth x body length/330 = body weight
75 x 75 x 64/330 = 1,091 pounds
For light horse foals from 1 to 6 weeks of age, a more accurate weight can be calculated using the following formula:
heart girth in inches - 25.1/0.07 = body weight 0.07
A heart girth measurement is the circumference of the chest just behind the elbow. Heart girth gives some idea as to the space available for the heart and lungs.
Heart girth also can be used alone to estimate body weight. Some tapes are sold that give a direct reading of girth to weight. If this type of tape is not available, an ordinary measuring tape can be used and the girth converted to body weight using Table 9-2.
Age, height, and weight are important when considering a horse for competition or for personal use. For horses of a known age, the terms colt, filly, weanling, yearling, and 2-year-old can be used until maturity. When accurate records are not available, age-related, specific changes in the teeth provide an accurate estimate of age.
The height of a horse relates to its use and value. Height can easily be measured. When scales are not available, the weight of a horse can be estimated from the girth measurement and a standardized table or from the girth and body length measurements and a standardized formula. Body weight is used for several management decisions.
Success in any career requires knowledge. Test your knowledge of this chapter by answering these questions or solving these problems.
True or False
1. A young female horse less than 3 years old is called a colt.
2. Horses have two sets of teeth.
3. The 12 front teeth of a horse are all called incisors.
4. Dental stars are the same as premolars.
5. A horse's girth can be used to estimate its weight.
6. List four reasons for needing to know the weight of a horse.
7. If the girth of a horse is 64 inches, about how much does it weigh?
8. If the girth of a horse is 70 inches and its body length is 62 inches, how much
does it weigh?
9. If a horse is 64 inches from the highest point of its withers to the ground, how many hands tall is it?
10. What term is used to describe tampering with the tooth cups to make the horse appear younger?
11. What is the opposite of monkey mouth?
12. -- is filing off the high spots in molars to improve chewing.
13. When do horses get their temporary and permanent centrals?
14. When do horses get their third permanent molar?
15. Discuss four key changes in teeth that are used to estimate the age of a horse.
16. Define these terms: foal, colt, stallion, mare, filly, weanling, and yearling.
17. Describe the importance of knowing the age of a horse.
18. What creates the dental star, and when does it first appear?
19. Where is Galvayne's groove, and when does it first appear?
20. Describe the changes in height and body weight as a foal grows.
1. Diagram the upper and lower jaw of a horse with a full complement of permanent teeth.
2. Compare the estimated body weight of a group of horses using the girth measurement method and the girth-body length formula.
3. Obtain an animal tooth and cut it in half lengthwise. Identify the parts of the tooth.
4. Sometimes the body weight of horses is given in kilograms and the height is given in centimeters. Develop a table of converted values for the following body weights given in kilograms: 80, 150, 220, 450, 500, and 550. Do the same for the following heights given in centimeters: 108, 126, 132, 139, 146, and 151. In this table, convert the weight to pounds and the height to inches and hands.
5. Using different colors of modeling clay, make a model of a tooth that shows what happens as the surface of the tooth wears away.
6. Using the information in Table 9-2, create your own tape for measuring girth that gives a direct reading of a horse's weight.
7. Obtain a horse skull and describe how it can be used to estimate age.
American Youth Horse Council. (2004). Horse industry handbook: A guide to equine care and management. Lexington, KY: Author.
Evans, J. W. (2000). Horses: A guide to selection, care, and enjoyment (3rd ed.). New York: Owl Books. Griffin, J. M., & Gore, T. (1989). Horse owner's veterinary handbook (2nd ed.). New York: Howell Book House.
Kainer, R. A., & McCracken, T. O. (1998). Horse anatomy: A coloring atlas (2nd ed.). Loveland, CO: Alpine Publications.
Lewis, L. D. (1996). Feeding and care of the horse (2nd ed.). Media, PA: Williams & Wilkins.
Price, S. D. (1998). The whole horse catalog. New York: Fireside. Internet
Internet sites represent a vast resource of information, but remember that the URLs (uniform resource locator) for World Wide Web sites can change without notice. Using one of the search engines on the Internet such as Yahoo!, Google, or About.com, find more information by searching for these words or phrases:
horse birth date
Table A-18 in the appendix also provides a listing of some useful Internet sites that can serve as a starting point for further exploration.
TABLE 9-1 Horse Teeth and the Approximate Age at Eruption Type Tooth Age Temporary 1st incisors (or Birth or first (Milk or centrals) week Deciduous) 2nd incisors (or 4 to 6 weeks intermediates) 3rd incisors (or 6 to 10 corners) months Canine (or bridle) 1st premolar Birth to first 2 weeks for 2nd premolar all premolars 3rd premolar Permanent 1st incisors (or 2.5 years centrals) 2nd incisors (or 3.5 years intermediates) 3rd incisors (or 4.5 years corners) Canine (or 4 to 5 years bridle) 1st premolar (or 5 to 6 wolf tooth) months 2nd premolar 2.5 years 3rd premolar 3 years 4th premolar 4 years 1st molar 9 to 12 months 2nd molar 2 years 3rd molar 3.5 to 4 years TABLE 9-2 Estimating a Horse's Weight from the Girth Measurement Girth Weight (Inches) (Pounds) (1) 32 100 40 200 45 275 50 375 55 500 60 650 62 720 64 790 66 860 68 930 70 1,000 72 1,070 74 1,140 76 1,210 78 1,290 80 1,370 (1) For pregnant mares, multiply the value by 1.02, 1.06, 1.11, or 1.17 for their weight at 8, 9, 10, and 11 months of pregnancy, respectively.
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|Publication:||Equine Science, 3rd ed.|
|Date:||Jan 1, 2008|
|Previous Article:||Chapter 8 Selecting and judging horses.|
|Next Article:||Chapter 10 Genetics.|