In the horse these maladies are only second in importance to those of the respiratory organs, while in ruminants they are equally frequent and important. The varying susceptibility of the digestive organs to disease in different families and the special proclivity of different parts of these organs may be, in great part, explained by the great variation in the food, by the relative extent of the gastro-intestinal surface, and by the amount of work devolving on the respective viscera.
In carnivora the entire gastro-intestinal surface is little more than half the area of the skin, for their rich animal food does not require a prolonged retention and an elaborate series of intricate processes to insure digestion and absorption. This system of organs is accordingly less liable to disorder in carnivora than in herbivora and omnivora. Add to this that the carnivorous stomach is very capacious relatively to the intestine, that the digestion of the great bulk of the food (nitrogenous elements) is nearly completed in this viscus, and that the contents of this organ are easily and completely discharged by vomiting whenever they prove irritating, and we have ample explanation of the comparative immunity of these animals from digestive disorders.
The herbivora stand at the opposite extreme, the gastro-intestinal surface being over double the area of the skin in the horse, and nearly three times that extent in the ox. The hard, fibrous and comparatively innutritious vegetable food of these animals necessitates its prolonged retention in the alimentary canal in order to the completion of digestion and the absorption of the nutritive constituents. Hence the great liability of the herbivora to diseases of the digestive organs.
Omnivora occupy a place intermediate between these two classes, as regards both the nature of the food and the extent of surface of the alimentary canal, and they are in similar ratio little liable to digestive disorders. They have besides in common with carnivora a great facility in the rejection of irritant matters by vomiting, and in thus protecting themselves against gastric and intestinal disorders.
A fair idea of the area of the intestinal surface may be given by stating the length of the canal relatively to that of the body:—in the dog : : 6 : 1, in the rabbit : : 10 : 1, in the ass and mule : : 11 : 1, in the horse : : 12 : 1, in swine : : 14 : 1, in the ox :: 20 : 1, and in the sheep : : 27 : 1. The calibre of the intestine varies however and with it the capacity. Thus in the relatively shorter intestine of the horse, the capacity is much greater in ratio with the size of the animal than is the relatively much longer intestine of the pig. The ox’s intestine though twice the length of that of the horse has little more than half the capacity.
Among herbivora the monogastric (horse, ass, mule), and polygastric (ruminants) animals manifest varying pathological susceptibility according to the relative development of the different digestive viscera and the habitual character of their food. The horse and other large solipeds have small stomachs (16 qts.) and capacious intestines (196 qts.). Digestion is restricted in the stomach and largely carried on in the spacious bowels. The small stomach requires to be frequently replenished in moderate amount, but, if this is secured, its liability to disease is slight while that of the intestines is very considerable. In the ox the stomachs have a total capacity of 252 qts., while that of the intestines averages 103 qts. In this animal the capacious and hard working stomach is a frequent seat of disorder, while the comparatively small intestines are to a large extent exempt. The small stomach of the horse is easily overloaded and disordered or paralyzed by an unusually full feed of grain when hungry, or one of some specially appetizing fodder, and the case is serious, as relief can rarely be obtained by vomiting. For the same reason fermentation of the gastric contents with evolution of gas and tympany usually proves fatal to the horse since relief by eructation is too often impossible. Cattle are fitted to live in damp localities where the cloven foot prevents sinking and getting bogged, and where they may draw in with the tongue a full mouthful of coarse herbage which they swallow with little mastication or admixture with saliva. This lodges in the first two stomachs, and if, from any cause, rumination is impaired, or suspended, it finds itself in conditions especially favorable to fermentation. The food too, as in the case of frosted roots, wet clover or partially ripened grain, etc., is often charged with ferments (bacteria) in a state of great vital activity, and hence the frequent tympanies of the ox. The ruminant is no less liable than the soliped to overload the stomach, and though the return of food from the first two stomachs to the mouth is a normal process, this is promptly arrested by the supervention of paresis in the overloaded and overdistended organs. This overdistension further tensely stretches and closes the lips of the œsophagean opening. The rapid swallowing of the food, with only one or two strokes of the teeth for each morsel, renders the large ruminant more liable to take in poisons, pins, nails and other injurious bodies, especially when hunger and the blunting of the sense of smell have been brought on by traveling on dusty roads. Again the large ruminants, and especially cows are wont to while away the tedious hours by chewing and unwittingly swallowing pieces of leather, cloth, bones, iron, etc. Once more the third stomach in which the food is compressed and triturated between the multiple folds, is normally comparatively dry, and is liable under dry, fibrous, heating or stimulating aliment, or in case of fever, to dry up in part or in whole, and to derange the whole process of digestion.
All herbivora are liable to disease from unwholesome fodder and the resulting affection may prove epizootic in connection with unfavorable seasons, or more local, from faulty cultivation.
The symptoms vary so much in connection with the seat and nature of the disease that it would be impolitic to attempt to generalize them.
DISEASES OF THE MOUTH.
Relative susceptibility to disease of the mouth: Food; irritants; bits; ropes; speculum; sharp metallic bodies; micro-organisms; functional; nervous.