It may be said that they are much deeper in the corner teeth when the colt is but a little past two years than they are when the colt approaches three years of age.
When the colt reaches the age of about two years, nine months, the roots of the central nippers are usually nearly absorbed and the permanent central nippers, if not already in evidence, will soon make their appearance.
When the colt is shedding teeth its mouth should be watched and, if the milk-teeth have not disappeared when the permanent ones have pushed through, they should be removed, as they only serve to irritate the gums and to prevent the animal from consuming the usual amount of feed. A little extra feed and care should be given the colt while it is substituting permanent for temporary nippers.
At about two years and nine months to two years and eleven months the center permanent nippers will appear, and at full three years of age the outer portion of the teeth and sometimes the inner also will be up and in wear. (Fig. 64.) These teeth are larger every way than were those which were supplanted. The lateral temporary nippers have changed shape and have lost all or nearly all their cups. The slight black indentations can hardly be called cups. The cups in the corner teeth are greatly reduced. If the colt be a male, small tusks are likely to be present or in process of coming through the skin of the jaw.
At about three years, nine months, the permanent lateral nippers appear. At four years of age they are fully up and in wear on the outside and sometimes on the inside. (Fig. 65.) The central nippers show a year's wear, and the cups are not so deep as they were when the colt was three years of age. The cups, or marks, have nearly or quite disappeared from the corner (milk) teeth, often nothing but a slight dark indentation being left. The tusks have enlarged, but are still sharp at their points and flattish on the inside. A side view of a four-year-old mouth is shown in Fig. 66. The crowns of the two temporary, or milk-teeth, one upper and one lower, come together closely over their entire surface, while the two permanent teeth do not yet meet at their posterior corners.
When the colt reaches the age of four years and nine months, the corner nippers make their appearance. When he reaches the full age of five years, the outer anterior portions of these teeth meet. (See side view of a five-year-old mouth, Fig. 68.) About one year of wear must take place before the corner teeth are worn level throughout their entire surfaces, the corner teeth when worn off level are one of the distinguishing marks of a six-year-old horse. At five years the central nippers have had two years' wear, and one more will virtually destroy the cups. They are also changing slightly in shape; they have become rounder on the inside and slightly shorter in their longest dimensions. The lateral nippers have also changed. They have been in use nearly one year. In about two years more the cups will have nearly disappeared. The corner teeth are longish from front to rear, and do not show change of form or indications of rounding up on the inside as do the older central nippers. The cups are deep and fresh, the corners are deficient, and in every way they show unmistakably that they are young teeth which have been subjected to little wear. The tusks have enlarged, but are not yet blunt, and prominently rounded on the inside, as they will be when the horse approaches his "teens." The permanent teeth are roughish, that is, have slight corrugations, while the temporary teeth are smooth on the outer surfaces.
Fig. 66. Side view of the teeth of a four-year-old horse.
Fig. 68. Side view of the teeth of a five-year-old horse.
The colt at five has a "full" mouth, and, with it, his name is changed to that of "horse." The female is no longer called a filley, but a mare, and the "entire" horse a stallion.
Sometimes horses have shelly teeth, in which case the inside of the corner teeth may not be up and in wear, in fact may never come up, and always have the appearance of a corner tooth that is not fully up. At rare intervals horses have what is known as "hawk-bill" mouths, that is, the upper incisors extend over the under ones; in which case it is difficult to determine the age after the horse has reached his sixth year. However, in horses, malformed teeth are rare.
Fig. 69 shows the teeth of the lower jaw when the horse reaches his sixth year. The marks, or cups, have disappeared, or nearly so, from the front nippers, have become shallower and smaller in the laterals, and the corner teeth are up on the inside and posterior corners..
No notches will yet be found in the upper corner incisors. The corner teeth are somewhat smaller than the laterals or the front teeth.
At six years of age, the wearing surfaces of these corner teeth come together throughout their entire length. The central teeth have made marked changes in shape, - they are becoming quite roundish on the inside, and the laterals are also somewhat modified, while the corner teeth are but slightly changed in general contour. During the year from five to six, the tusks have become slightly larger, rounder and blunter. If the horse's lips be parted, and the mouth viewed from the front, the teeth, especially the central ones, will appear darker colored and longer than they did a year or two years previous, due to shrinking or receding of the gums. Compare Figs. 64, 65, 67.
Fig. 70. Side view of the teeth of a six-year-old horse.