(Note: The text and images are taken from “A Study of Farm Animals,” by Charles S. Plumb, 1924. Click on photos to enlarge.)
“The use of the horse, in spite of the automobile, is very general in both town and country. He is suited to do many things for which the motor is not fitted. He is a more economical producer of power in short hauls than is the motor, and he is as necessary as ever on the hill farms and where small areas are cultivated. According to the 1920 census we had in the United States some 20 million horses and over 5 million mules. These horses had a farm value of $2,000,000,000, and the mules were valued at half a billion dollars, so we may see that the production of the horse in America is a great industry….
The work of the horse and what he can accomplish depends upon his weight, his muscular development, and his endurance. What is knows as horse-power, is the power necessary to raise 33,000 pounds at the rate of one foot a minute against gravity. The real measure of horse-power is based on the unit of a foot-pound, shown in the power manifested in raising a pound one foot. The horse works in different ways, no matter what his type, weight or size….
Feeding standards for the horse have been in use for a long time, and, on the basis of what has already been stated, the necessity for different standards is very apparent. Here weight and work are the two vital factors. The following is the modified Wolff-Lehmann standard for horses, as given by Henry and Morrison (Feeds and Feeding, 1917)

The preparation of the feed for a horse is important. The horse has a comparatively small stomach, and so, as his work increases, concentrates should more or less replace roughage. Food is prepared in several ways. Dry roughage is often chaffed, that is, cut or shredded. Chaffing reduces the work of the horse for the reason that the more the roughage is torn to pieces by mechanical means, the less labor will be required of the horse in breaking it up. Men who care for horses often make hay or straw more palatable by chaffing, then mixing with concentrates, and dampening the mass with a light sprinkling of water. Thus prepared, more roughage is consumed than would be the case otherwise, and the sprinkling reduces the dust, which is injurious to horses. The grinding of grain for horses is unnecessary, unless in the case of old animals with poor teeth. Whole grain is appetizing to the horse, he grinds and breaks it up easily with his teeth, and it digests efficiently as thus fed. Crushing grain may be desirable, and the author has known of city stables where oats were run through a mill and crushed, and as thus fed gave better returns, in the opinion of the management, than were secured from oats fed whole. Cooking of feed has been resorted to by horsemen in the past, more especially in Europe, but this process affects the digestibility of the proteids, so the practice is undesirable. What is known as a bran mash, that is, wetting bran with hot water to make a thick, fairly moist feed, is practiced. If fed at regular periods, as, for example, once a week, it has a cooling, laxative effect. Bran mash is relished by horses, and is popular as an occasional feed. The soaking of feed may sometimes be desirable, especially in spring when feeding very hard, dry corn or barely.

The feeds most desirable for horses vary according to condition of age, work, and locality. Oats in the grain is the favorite food for horses both in America and Europe. There is no likelihood of danger from overeating oats, they are much relished, and from them the horseman looks for greater activity than from most feeds. Dry ear corn is popular in the corn-growing sections, especially in the South and Central West, where hundreds of thousands of horses see no other kind of grain. Experiments at the Ohio station, conducted by Prof. Carmichael, show no important difference in the feeding value of corn and oats, as fed work horses under equal conditions. Barley is fed horses in some parts of America, Europe, and northern Africa, and meets with favor. Wheat and rye are too pasty for satisfactory horse feed. Wheat bran has been fed mixed with oats and corn, and gives good results. Corn meal is too heavy for a horse feed, unless mixed with bran, oats, or chaffed hay, when it will do very well. What is known as chop feed for horses in some sections consists of varying portions of oats and cracked or crushed corn, the percentage of one to the other depending upon the value of each fed in the market. As a rule, two thirds oats and one third corn is a good proportion. Linseed meal is a most excellent feed to be given in small amount once daily, as, for example, a half pound a day. This is a fine appetizer, and tends to make the skin mellow and the hair sleek and glossy. Condition powders or prepared condimental stock foods are not to be recommended. The lindseed meal will largely serve the same purpose and in fact is a popular conditioner.
Of all the dry roughages, timothy hay in the East is a leading favorite. It is usually free from dust and is relished by the horse. Any well cured, sweet grass, however, will usually prove satisfactory horse roughage. Good dry corn stover is excellent horse feed. Alfalfa hay or red clover are rich in protein and lime, and may be fed to advantage when care is used. Dust must be avoided, and the leaves should be free of mildew or mould. A combination of alfalfa or clover with corn makes nearly a balanced ration for the work horse. There is considerable difference of opinion among American horsemen as to the suitability of these feeds for horses, but in France alfalfa has long been extensively fed to horses, while in the western United States it has been shown to be an excellent roughage for horses when well cured. Corn silage may be safely fed to horses in limited amounts, but it is important that it be bright and well cured, free from all mouldy matter; otherwise serious results may occur. Horses do well on pasture, especially of mixed grasses or of some sort of blue grass, of which Kentucky blue is the more common sort.”