A practice in which some horses indulge has the effect of wearing down the incisor teeth, especially towards the outer edge (fig. 129). It is very seldom, however, that any dental disease or derangement arises out of it.
In connection with diseases of the nervous system it is necessary to refer to certain abnormal actions commonly described as nervous habits, which are not usually recognized as diseases, but which, as they are not normal, i.e. are not in accordance with the rule as applied to the actions of healthy animals, must be classified as abnormal.
"Cribbing" or "tic", "wind-sucking", and "weaving" may be taken as examples of diseases which are more or less connected with some ill-defined derangement of the nervous system. Tic or cribbing has been carefully studied in its various forms by Continental veterinarians. Friedrich Berger and Frohne, in their work on the pathology of the domestic animals, allude to the causes of cribbing as being complex and variable in their nature. Idleness is said to be one cause of the acquirement of the habit. Horses, like other creatures, are supposed to invent some kind of pastime when left alone in a stall or box, and the manger, drinking-trough, or piece of chain or rope lends itself to this kind of indulgence, In the case of some animals it seems that no assistance from external objects is necessary, as they succeed in performing the actions of a crib-biter without seizing the manger with their teeth or obtaining any other support. By contracting the muscles of the neck they contrive to keep the head in a fixed position, and can make the peculiar noise which is common to crib-biters.
Among the causes of cribbing heredity is referred to as having considerable influence. Horses it is said become crib-biters and wind-suckers apparently from imitation, although it would seem that a certain amount of nervous excitability is necessary as a predisposing cause, as it may be that only one animal out of a very large number which are exposed to the same temptation acquires the habit.
The habit of cribbing or wind-sucking has somewhat fancifully been attributed to the use of a curry-comb in the act of cleaning, as when the instrument is used with much force it causes a good deal of irritation, which the animal indicates by biting at anything within its reach; and it is supposed that the habit of biting and making spasmodic movements of the lips and other parts at the same time might finally lead to cribbing.
Fig. 179. - Throat-strap for Crib-biting.
Cribbing and so-called wind-sucking induce occasional attacks of colic from the quantity of air which is developed in the stomach, and both are associated with an irritable condition of the mucous membrane of the digestive organs, which we believe to be a cause of these remarkable acts. In a legal point of view cribbing and wind-sucking would amount to unsoundness if that term is construed strictly, and in some parts of the Continent the habit is recognized as sufficient to constitute a breach of warranty. In any case, a horse addicted to crib-biting or wind-sucking, or both, can hardly be said to be as useful for its intended purpose as an animal which is free from such defects. If there were no other objection to be urged, it would be sufficient to point to the well-known fact that the animal loses flesh and becomes thin.
The owner of a crib-biter or wind-sucker is very anxious to find out some means of cure, and various mechanical appliances have been suggested for the purpose. The plan of using movable mangers and troughs, and avoiding all projecting posts on which the animal may place his teeth and get a point of support, has been said to be successful in cases of crib-biting, but it is obviously of no use in the case of a wind-sucker, which does not require such assistance. In most instances of crib-biting and wind-sucking the ordinary throat-strap (fig. 179), which is arranged to be buckled round the throat, acts as a preventive, but to be effectual it must be constantly employed while the animal is in the stable.
The other habit which has been referred to under the term weaving, consists in swaying the head and fore part of the body from side to side like a bear. Although perhaps less objectionable than wind-sucking, it is, nevertheless, a serious fault, since the animal which is addicted to it is constantly using his legs when he should be resting them. Weaving is most commonly seen in horses which are tied to the manger by means of two side-ropes fixed to the head-collar and carried through rings on each end of the manger. At the end of each rope a perforated wooden block is fixed on purpose to prevent the removal of the halter-ropes from the rings.
The habit of weaving may sometimes be corrected by keeping the animal in a loose-box without any head-collar or halter-ropes. This, however, is not always successful, as in some cases the animal continues the lateral movements of the head even when it is left altogether without any means of restraint.
OEDEMA OF CHOROID PLEXUS.