Goats, being herbivores, obtain the greatest portion of their sustenance from plant materials which are of low or no nutritional value to man. Through mastication, regurgitation, and rumination of these materials by their teeth, especially the molars, the plant materials are reduced to small particle sizes, thus increasing their relative surface areas and making them easier to be digested. Much of the grinding action of the teeth is the direct result of their surface angles and rotary-like movements of the lower jaw. The combination of lateral and vertical movements is due to the fact that upper and lower jaws are not perfectly matched, but the lower jaw is somewhat smaller than the upper. Food material can therefore be chewed only from one side of the mouth at a time through a lateral grinding action. Such will result in a pattern of wear that causes the teeth to develop points on the outer edges of the lower molars. Only after action of the teeth has reduced plant materials to a finely ground pulp can effective digestion begin. With goats as well as with other ruminants, complete chewing is not done at the actual time of grazing. Later, at the animal’s leisure, the materials are ruminated and re-chewed until the feed particles are small enough to be passed on in the digestive tract.
Throughout the process of mastication, the tongue and cheeks are constantly in motion keeping the feed material moving between the teeth until it has been ground well enough to be formed into a bolus which then can be moved back in the mouth and swallowed. Mastication is basically a voluntary act under the control of brain centers although in practice it appears more like an autonomic process. Mastication is dependent upon sensory stimulation, with the fifth cranial nerve (trigeminal) being mainly responsible. Effector impulses travel the route of this nerve to the elevators of the jaws and along the seventh cranial nerve (facial) to the digastric muscle, and the lip and cheek muscles. Impulses may also travel the 12th cranial nerve (hypoglosseal) to the muscles of the tongue. Teeth are generally classified as being of two types according to their permanence: the temporary milk teeth and the permanent adult teeth.
MILK TEETH – Milk teeth are present either at birth or shortly afterwards and will remain for about a year before replacements with permanent teeth begins. Milk teeth are not as hard as adult teeth since adult teeth are expected to remain and function throughout the life of the animal.
The continual growth of the tooth root, along with other factors, serves to push the crown of the milk teeth up and out of their sockets, through the overlaying segments of the dental sack and gum. The actual time period for the erupting or “cutting” of the teeth, while providing a general indicator of age in the goat, is not the same for all goats. Variances according to breed, climate and nutritional conditions will cause differences in the actual time of teeth eruption among individual goats. This is the reason that goat shows should never split classes among two and four tooth animals as they do not represent differing age classes.
ADULT TEETH – Permanent teeth undergo more progressive development. They press against the tissues of the milk teeth and cause the roots of the milk teeth to break down. This in turn releases the dental pulp from its anchorage in the gum. With tissues loosening and exerted pressure from the rising permanent teeth, the milk teeth are shed from the jaw.
Tissues surrounding the developing teeth undergo a developmental process that differentiate the mesenchymal tissue from the connective tissue which makes up the dental sack. The dental sack, where the teeth roots will be, takes on three important functions. The inner cells differentiate into a layer of cementoblasts at the time of eruption. As the epithelial sheath breaks down and disintegrates in a downward direction, the cementoblast cells deposit cement upon the dentine of the teeth. This deposition occurs from the neck region downward. The surface of the dental sack becomes active in bone production as the calcification process of the jawbone progresses. The tooth becomes surrounded by spongy bone, occupying its own socket. The fibrous sack itself forms a thin membrane which serves to hold the tooth in place by embedding some fibers in the cement and others in the bony wall of the socket.
Teeth can be further classified into three groups according to the way in which they grow: true teeth, constantly growing teeth, and constantly erupting teeth. Of the three, goats have two: true teeth and constantly erupting teeth.
TRUE TEETH – The incisors of the goat are considered to be true teeth in that they possess a crown, a root and a neck, growing to adult size before they begin to gradually wear away.
ERUPTING TEETH – Constantly erupting teeth are found in the goat in the molars. This type of tooth is made up of layered masses, possessing very long roots and no real neck. As the goat ages, these teeth are gradually forced upward to account for wear by the deposition of bone in the jaw below them. In the case of very old animals, such teeth may accordingly be forced out by this rising action.
TOOTH COMPOSITION – True teeth are composed of five parts and four tissues. Constantly erupting teeth have but four parts, as they have no neck. The crown of the tooth is the part which appears above the gum line, while the neck is located at the gum line. It appears as a narrowing that separates the crown from the root. Implanted into the tooth socket of the jaw is the root, which may be either singular, paired or multiple, depending upon what type of tooth it is. The central cavity of the tooth that runs from the base of the root up into the crown is known as the pulp cavity, containing the dental pulp, vessels and nerves. This cavity is large in young animals but over time it becomes infiltrated with dentine and may be completely filled in old goats. The table surface is that part of the tooth that is actually used for grinding or tearing of the food.
Cement is the second hardest tissue and is found as the outermost layer covering the tooth. In true teeth, this yellow to black substance covers the roots only. Enamel, the hardest tissue of the body, is the next layer, covering the dentine of the tooth. Its coloration is about that of ivory. Under the enamel lies the tissue that forms the bulk of most teeth, dentine. This substance, which is hard and yellowish, covers the pulp of the tooth, supporting numerous blood vessels and nerves.
DENTAL DEVELOPMENT – All ruminants including goats lack upper incisors. Instead there is a hard dental pad on the frontal part of the upper jaw which serves in place of teeth. The dental formula for goats is 0033/4033. The formula is derived from the number of teeth the animal has in one half of the upper and lower jaws. The four digit system for each jaw half is beginning in the jaw center with the numbers from left to right reading incisors, canines, premolars and molars, respectively. The numbers to the left of the “/” represent one half of the total teeth of the upper jaw, and the numbers to the right of the “/” one half of the total for the lower jaw.
The mature goat will have therefore, a total of 32 teeth, of which eight are lower incisors and the rest are arranged in four groups of six molars each. The appearance of the two first teeth (milk teeth incisors) occurs at birth to one week of age. The second pair of milk teeth incisors appears at about one to two weeks of age, while the third and fourth milk incisors appear at two to three and three to four weeks of age, respectively.
The pattern for the eruption of permanent incisors, according to the established Dairy Goat guidelines is between one 12 and 18 months of age for the first pair of incisors, 18 months to two years for the second pair, two and a half to three years for the third and three and one half to four years for the fourth set of incisors. In the cashmere goat industry, things are quite different.
Copyright 1994 Capricorn Press. Not to be reproduced without express written consent of Capricorn Press.