Читать книгу Cattle and Their Diseases - Robert Jennings - Страница 19

It is of the utmost importance to be able to judge of the age of a cow. Few farmers wish to purchase a cow for the dairy after she has passed her prime, which will ordinarily be at the age of nine or ten years, varying, of course, according to care, feeding, &c., in the earlier part of her life.

The common method of forming an estimate of the age of cattle is by an examination of the horn. At three years old, as a general rule, the horns are perfectly smooth; after this, a ring appears near the nob, and annually afterward a new one is formed, so that, by adding two years to the first ring, the age is calculated. This is a very uncertain mode of judging. The rings are distinct only in the cow; and it is well known that if a heifer goes to bull when she is two years old, or a little before or after that time, a change takes place in the horn and the first ring appears; so that a real three-year-old would carry the mark of a four-year-old.

TEETH AT BIRTH.

SECOND WEEK.

The rings on the horns of a bull are either not seen until five, or they cannot be traced at all; while in the ox they do not appear till he is five years old, and then are often very indistinct. In addition to this, it is by no means an uncommon practice to file the horns, so as to make them smooth, and to give the animal the appearance of being much younger than it really is. This is, therefore, an exceedingly fallacious guide, and cannot be relied upon by any one with the degree of confidence desired.

The surest indication of the age in cattle, as in the horse, is given by the teeth.

The calf, at birth, will usually have two incisor or front teeth—in some cases just appearing through the gums; in others, fully set, varying as the cow falls short of, or exceeds, her regular time of calving. If she overruns several days, the teeth will have set and attained considerable size, as appears in the cut representing teeth at birth. During the second week, a tooth will usually be added on each side, and the mouth will generally appear as in the next cut; and before the end of the third week, the animal will generally have six incisor teeth, as denoted in the cut representing teeth at the third week; and in a week from that time the full number of incisors will have appeared, as seen in the next cut.

THREE WEEKS.

MONTH.

FIVE TO EIGHT MONTHS.

TEN MONTHS.

TWELVE MONTHS.

FIFTEEN MONTHS.

These teeth are temporary, and are often called milk-teeth. Their edge is very sharp; and as the animal begins to live upon more solid food, this edge becomes worn, showing the bony part of the tooth beneath, and indicates with considerable precision the length of time they have been used. The centre, or oldest teeth show the marks of age first, and often become somewhat worn before the corner teeth appear. At eight weeks, the four inner teeth are nearly as sharp as before. They appear worn not so much on the outer edge or line of the tooth, as inside this line; but, after this, the edge begins gradually to lose its sharpness, and to present a more flattened surface; while the next outer teeth wear down like the four central ones; and at three months this wearing off is very apparent, till at four months all the incisor teeth appear worn, but the inner ones the most. Now the teeth begin slowly to diminish in size by a kind of contraction, as well as wearing down, and the distance apart becomes more and more apparent.

From the fifth to the eighth month, the inner teeth will usually appear as in the cut of the teeth at that time; and at ten months, this change shows more clearly, as represented in the next cut; and the spaces between them begin to show very plainly, till at a year old they ordinarily present the appearance of the following cut; and at the age of fifteen months, that shown in the next, where the corner teeth are not more than half the original size, and the centre ones still smaller.

EIGHTEEN MONTHS.

TWO YEARS PAST.

The permanent teeth are now rapidly growing, and preparing to take the place of the milk-teeth, which are gradually absorbed till they disappear, or are pushed out to give place to the two permanent central incisors, which at a year and a half will generally present the appearance indicated in the cut, which shows the internal structure of the lower jaw at this time, with the cells of the teeth, the two central ones protruding into the mouth, the next two pushing up, but not quite grown to the surface, with the third pair just perceptible. These changes require time; and at two years past the jaw will usually appear as in the cut, where four of the permanent central incisors are seen. After this, the other milk-teeth decrease rapidly, but are slow to disappear; and at three years old, the third pair of permanent teeth are but formed, as represented in the cut; and at four years the last pair of incisors will be up, as in the cut of that age; but the outside ones are not yet fully grown, and the beast can hardly be said to be full-mouthed till the age of five years. But before this age, or at the age of four years, the two inner pairs of permanent teeth are beginning to wear at the edges, as shown in the cut; while at five years old the whole set becomes somewhat worn down at the top, and on the two centre ones a darker line appears in the middle, along a line of harder bone, as appears in the appropriate cut.

THREE YEARS PAST.

FOUR YEARS PAST.

FIVE YEARS PAST.

TEN YEARS PAST.

Now will come a year or two, and sometimes three, when the teeth do not so clearly indicate the exact age, and the judgment must be guided by the extent to which the dark middle lines are worn. This will depend somewhat upon the exposure and feeding of the animal; but at seven years these lines extend over all the teeth. At eight years, another change begins, which cannot be mistaken. A kind of absorption begins with the two central incisors—slow at first, but perceptible—and these two teeth become smaller than the rest, while the dark lines are worn into one in all but the corner teeth, till, at ten years, four of the central incisors have become smaller in size, with a smaller and fainter mark, as indicated in the proper cut. At eleven, the six inner teeth are smaller than the corner ones; and at twelve, all become smaller than they were, while the dark lines are nearly gone, except in the corner teeth, and the inner edge is worn to the gum.