So far nothing has been said about determining the age of horses. A discussion of this subject has been purposely deferred until the limbs, and particularly the feet, have been examined. If these indicate that, in general, the bony structure is softish and of open texture, then it may be concluded that the teeth are of the same general character. The teeth of horses which have bones of somewhat open structure are likely to indicate that they are slightly older than they really are; while the teeth of horses whose bones, as indicated by legs and hoofs, are of fine and close texture may indicate them to be younger than they really are. All this applies to horses which have passed their eighth year, there being certain characteristics and changes in the teeth up to about the eighth year by which the age within a few months may be accurately determined. After the horse has passed the eighth year, it is sometimes difficult, to determine his true age by the teeth. Experts may come within a year or two of it until the horse becomes quite aged, when he may be said to be sixteen past or eighteen past, and the like; but how much past may not certainly be known from the appearance of his teeth. The texture of the bone, the breeding, the kind of food the horse has eaten, and other conditions, have more or less influence on the teeth; therefore in the old horse the teeth serve to indicate age only in a general way.
The horse when full-grown has forty teeth incisors 6/6, canines (incipient in the females), 2/2, molars 6/6, 6/6=20/20=40. As the incisor teeth only are usually inspected when the age of the horse is to be determined, they alone will be discussed here. The colt is provided, before the end of the first year, with twelve temporary incisor or milk-teeth. The difference in size of the jaw-bone of the foal and the horse makes a change from milk to permanent teeth necessary.
Usually from one to two weeks after the foal is born, two center nippers in each jaw are plainly visible and appear as shown in Fig. 59. It will be noticed that these teeth are long from right to left and have well-defined cups, or "maiks," and that they show little or no wear. These characteristics should be noted carefully, for all temporary and permanent teeth when new have pronounced distinguishing marks. If the age of the colt and horse is to be determined with any degree of accuracy, not only the number but the shape, character and various changes, as the teeth progress in age, should be most carefully noted.
At from four to six weeks of age, by reason of use the first pairs of nippers will have been worn down level, that is, the inside of the teeth will show level with the outside. The outside edges of new teeth are always more forward than the inside edges. It should also be noted that these new teeth are fully twice as long laterally as they are thick. In Fig. 60 are shown the lower nippers when the colt is from four to six weeks of age. The central pair of nippers shows wear and the lateral pair is through, but the inside and the posterior corners are not fully up and show clearly that they have not been in wear. The permanent teeth show the same characteristics when new; that is, the inside and the posterior corners do not come up nor come in wear as soon as do the outside and the anterior corners. Note that the cups, or marks, in the central pair are not quite so deep nor so long as they were when coming into wear, as shown in Fig. 59.
When the colt reaches eight to ten months of age, the teeth will appear as shown in Fig. 61. The corner nippers are up but not fully in wear on the inside and the posterior corners. The posterior corners of the last pair of nippers, both in the colt and horse, come up and get in wear more slowly than do the posterior corners of lateral nippers. Note, too, the changes which have taken place in the cups and in the shape of both the central and the lateral nippers.
It would be well, before proceeding further, to turn to Figs. 74 and 78 and notice how the wear from year to year results in a change of the form of the tooth and, in time, in obliterating the cups, or marks.
Note also the difference in the shape of the root of the permanent tooth, Fig. 74, and the temporary tooth , Fig. 62. The root of the latter is much smaller and shorter than the former. It also has a distinct neck, which, however, is not easily discovered at first, as the gums partially cover the neck. As the milk-tooth approaches three years of age, its roots are absorbed rapidly and the neck is easily discovered. By the time the permanent tooth is ready to appear, the root of the temporary tooth is nearly absorbed and little remains besides that portion which is above the neck. The temporary teeth not only have a distinct neck but are smaller, smoother and lighter colored than the permanent teeth. These differences may assist the beginner in distinguishing the two kinds of teeth and in determining age.
Fig. 62. A temporary, or milk tooth.
At the full age of one year, the marks in the central nippers will be much shorter and fainter than they were at first. The lateral nippers will show wear, the marks will be longer and more pronounced than in the central nippers, but they will be shorter and less indented than in the younger corner teeth. All of the nippers will be up and the corner ones will be worn level; that is, their posterior corners will be fully up but not worn quite as much as shown in Fig. 63. It requires some care to determine accurately the age of the colt when it has passed its first year and up to the time the central nippers are replaced by permanent ones. It may be said, however, that the teeth show wear and have something of the appearance of a six-year-old mouch in miniature; but, with careful inspec-tion, many minor differences can be observed. The teeth are shorter, that is, show less above the gums, are smaller than those of the six-year-old animal and have a distinct neck. They are lighter colored than are those of the horse of six years of age. If the teeth of the two-year-old colt (Fig. 63) be compared with those of the one nearly a year old (Fig. 61), it is seen that the cups, "marks," of the central nippers of the two-year-old have nearly or quite disappeared, although a little discoloration usually remains in the center of the teeth. There is still a slight mark in the laterals, and the marks in the corner nippers are fairly deep.