The woody-fibre or cellulose contained in varying proportion in different kinds of provender, although possessing in some degree a composition similar to the non-nitrogenous constituents, cannot be considered altogether as aliment. Its function in the animal economy is to stimulate digestion and separate the richer particles of the food. The ash and salines furnish material for renewal of the bodily frame, and assist in the elaboration of secretions.
The amount of food constituents needed to maintain the functions of the body in proper working order, without the animal being required to undergo any extra exertion, has been variously computed; but it is now pretty well ascertained that the essential diet for a horse, in a state of quietude, for twenty four hours, should be made up as follows : -
Being a total of Food, free from water, of
This is calculated to possess potential energy capable of producing force equal to 27,855 foot-tons. And if the weight of the horse is estimated at 1,000 lbs., he would require 87.3 grains for each pound of body weight; or the whole body would require about 1 .80th part of its weight in food every twenty-four hours, the animal undergoing no toil of any kind. A pony weighing 440 lbs. requires forty-six grains of nitrogenous material for each 2 lbs. 3 1/4 oz. of weight.
This essential diet is supposed to be theoretically totally devoid of water, but in reality it would contain from fifteen to twenty per cent. of that fluid; so that, to allow for it, something like 1.87 lbs., or 2.49 lbs., must be added to the 12.472 lbs. just referred to. Such is the subsistence ration, with its heat-forming and energy-producing constituents, which will maintain the vital powers of a horse in a normal condition for a day. The additional food required to enable the body to perform what may be called "external work," in contradistinction to that performed within the body, and which may be designated "vital" or "internal work," must depend upon circumstances, such as the amount and severity of the labour, and the conditions in which it is performed, as season of the year, locality, etc.
The weight of the horse, it may be noted, does not give us F an exact estimate of the amount of food required, as the smaller the animal the larger are his requirements in propor-tion, there being a larger expenditure in the latter than the former, because of the vital activity being greater, owing to the comparatively more extensive surface exposed.
Horses will perform a certain amount of slow work on hay alone, as it is a typical food for herbivorous animals, the substances required by the body existing in it in the best proportions; but to do this a large quantity is needed, as for a moderate-sized horse from 18 lbs. to 20 lbs. of hay are demanded as essential diet (i.e., to perform "internal work") for twenty-four hours.
But, as has been stated, hay alone will not suffice - unless in such quantity that its bulk would prove injurious for heavy work; and by a mixture of foods we can supply a better diet, and one which will meet all requirements. Indeed, it has been asserted that a cheaper and quite as nutritive " essential " diet for a horse than 20 lbs. of hay is one composed of 11 1/4 lbs. of hay and 6 1/2 lbs. of straw.
The amount of "variable" diet for working horses depends upon the degree of labour performed, and the kind of labour; if this be slow and prolonged, there is less waste of energy and of tissue than when it is brief and severe. It has been calculated that the useful work of a horse, which would be represented by 100, with a velocity of two miles per hour, would not be more than 51, with a velocity of 7 1/2 miles, or more than 7, with a speed of 11 1/2 miles an hour. This calculation is sup-ported by the fact that the amount of food necessary for slow work for ten hours will not suffice for more than five hours' exertion at a trot. "With increased speed in work, there is an increased demand for nitrogenous substances; and in a trot or any fast pace it has been shown that for each 7,233 footpounds of energy expended, 15 to 24 grains of albuminoids must be allowed.
In calculating the diet for exertion, it has been estimated that work at a walk requires from 6 3/4 grains to 9 grains of nitrogenous matter for 7,233 foot-pounds of work performed; and that work at a trot or fast-pace demands from 15 3/4 grains to 24 grains for every 7,233 foot-pounds of work.
With regard to the amount of force exerted by horses during labour, which it is important to know in order to judge of the quantity of food required, it may be mentioned that a one-horse engine working for ten hours per day raises 19,799,360 pounds one foot high-this being the calculated amount of energy expended in ten hours if it could be all at once exercised. But this is probably much more than a horse could exert; a very hard day's work would in all likelihood not be more than 16,400,000 foot-pounds, which would be exercised by a horse pulling a load along at a walk for eight hours. Eight hours' slow walking, with a traction force of 100 lbs., is equal to 8,436,571 foot-pounds per diem. Slow farm work is equal to 11,211,000 foot-pounds a day. With regard to fast work, the amount of foot-pounds raised is less, for the effort required is sudden, and the waste of tissue or force is consequently greater. The actual amount of work done is less, for the reason that the animal cannot sustain the effort, and owing to the greater waste incurred more food is needed. A Paris omnibus horse is calculated to expend 4,377,433 foot-pounds per diem; in a mail-cart the amount was found to be 5,786,000.
But it is evident that work both at a trot and walk must vary considerably, depending upon the speed, and also the weight carried or drawn. However, it has been suggested that the following estimate is fairly correct: -
A hard day's work for a horse at a walk would be... ... ... ...
A moderate day's work, ditto
A hard day's work for a horse at a trot of fast pace would be ... ...
A moderate day's work, ditto
The following table shows the amount of food required by a horse under different conditions of labour, the proximate principles of the diet being given: -