Water, whether drunk by the horse or whether it forms a constituent of his food, is evidently necessary for the repair of broken-down tissue, and for maintaining the blood and other fluids of the body in a properly diluted condition, especially when we consider that water forms about three-quarters of the entire weight of the adult horse, and that a large quantity of water is given off by the lungs, skin, and kidneys. The presence of an unduly high proportion of water in fodder, injuriously hastens the passage of the food through the stomach and intestines, checks the secretion of saliva, and impedes digestion by diluting the digestive juices, thus hindering their action on the nutritive matter. If the total proportion of water be too small, the dung will probably be passed out too slowly, and the formation and absorption of deleterious matters by the intestines will be promoted. When requirements of work demand that a horse shall eat a large quantity of corn, the consumption of which will fully tax his digestive powers, it is necessary that the corn shall be given in the state in which it can be most easily digested, namely, dry. Hence, if we see fit to increase the proportion of water in the food, we can give "green meat" at a time when it will not interfere with the digestion of the corn, say, an hour before or two hours after feeding on corn.

For practical purposes we may call a food watery when it contains more than 25 per cent. of water (see tables on pp. 62 and 63); and dry, when the percentage is equal to or less than 25. A good ordinary working diet will contain about 25 per cent. of water, as we may see from the following calculation: -

A high diet, the dryness of which should not, I think, be often exceeded, would be : -

If carrots are withheld, a bran mash, which is generally allowed once or twice a week, would add to the water in the food. The addition of water confers laxative properties on the bran, which, when given dry, has not this effect.

A full diet containing an undue proportion of water would diminish the power of breathing by increasing the volume of the stomach and intestines. We may here note that the interior of the body is divided by the diaphragm (midriff) into two cavities : the thoracic cavity (chest), and the abdominal cavity (abdomen); the former containing the lungs and heart; and the latter, the stomach, intestines, liver, spleen, bladder, and other organs. The front portion of the stomach and intestines lies against the rear surface of the diaphragm, which is a cone-shaped muscle that has its apex pointing forwards, and its base attached to the spine and to the ends of the ribs. The act of inspiration (taking air into the lungs) is effected by muscles which increase the size of the thoracic cavity. By diminishing the pressure of air in that cavity, these muscles cause air to pass from outside, through the nostrils, windpipe and bronchial tubes, and to enter the air-cells of the lungs, which then become inflated. Speaking generally, the muscles in question may be divided into two sets, namely, those which by contracting enlarge the size of the chest by drawing the ribs forward (thoracic breathing), and the diaphragm, which by contracting performs a similar office by pushing the contents of the abdomen in a backward direction (abdominal breathing). Expiration (expulsion of air from the lungs) takes place by the two sets of muscles ceasing to contract and thus allowing the ribs to fall back into their previous position, while the diaphragm and its contents move forward into the chest. As the action of breathing depends on the ability possessed by the chest of increasing its internal capacity during inspiration, it follows that the greater the bulk of the stomach and intestines, the more will the power of breathing be restricted by the impediment offered to the contraction of the diaphragm. As the full action of the diaphragm is demanded during health only when the power of breathing is considerably taxed (forced breathing), this question of undue bulk of the stomach and intestines as affecting breathing, is essentially one of work. In pleurisy, the breathing is chiefly abdominal, because any movement of the ribs will cause pain to the inflamed membrane which lines the ribs.

As almost all the nitrogen of the broken-up nitrogenous matters of the body is contained in the urine; we can, by making an analysis of that fluid, find out the disintegrating effect which work has on these substances. Contrary to what we might have expected, such an analysis shows that a horse, under ordinary healthy conditions, excretes as much, or nearly as much, nitrogen along with his urine during rest, as he does when in fairly strong work. The expenditure is increased to some extent during severe and continued labour, and in a marked manner during extreme starvation. Work has a far greater effect in reducing the bodily fat than in breaking up nitrogenous tissue, the larger portion of which consists of muscle (the lean of meat). Besides, no advantage is obtained, from a working point of view, by increasing beyond a narrow limit the quantity of nitrogenous matter in the food. On the other hand, the amount of starch, sugar, and fat which the animal can eat with benefit, is proportionate to the severity of his work. Although horses cannot, like carnivora, digest a comparatively large quantity of fat, fat is a necessary constituent of their food, and cannot be wholly replaced by starch, sugar, or nitrogenous matter without injury to the animal's health. The large percentage of fat in oats and maize undoubtedly enhances the value of these grains as foods for horses.

When animals are deprived of food for a long period, there is an abnormally large expenditure of bodily fat, which has to furnish as far as it can, the actual energy required for the work of the body and for the maintenance of internal heat; but the variation in the excretion of nitrogen in the urine is trifling, until the store of fat has been practically exhausted, and then a rapid waste of nitrogenous tissue ensues up to the time of death. It therefore appears that the chief feeding value of nitrogenous matter in the food is to build up tissue; and that of starch, sugar, and fat, to furnish energy to the body. This conclusion as to the building up of tissue being the principal office of nitrogenous food, is supported by the experiments made by Sanborn and Henry on growing pigs; for those which were fed on food rich in nitrogen had larger muscles and stronger bones than those fed on food rich in carbo-hydrates, but poor in nitrogen. These deductions are amply borne out by the results of practical experience; for we all know that a horse cannot undergo severe and prolonged exertion successfully, unless he has been fed for some time previously on a highly nitrogenous diet, or, to use a stable expression, has had plenty of corn "put into him." We also know that old horses which have been at grass and without corn for some months, take a long time to regain their former working condition; and that the best way to prevent them, when at grass, from losing muscular strength and staying power, is to feed them on a fair amount of corn. Supposing that a hard-working animal has his muscles fully developed, he will manifestly be in greater need of food which is rich in energy-producing material, than of a diet rich in nitrogen; especially when we take into consideration the comparative permanency of nitrogenous tissue. This statement would, I think, lead us to the conclusion that highly nitrogenous foods, such as beans and peas, are more useful for horses which are low in muscle, whether they are at work or idle, than for hard-worked muscular animals.