GRASSLAND CROPS AS FEED FOR HORSES

P. Earle

THE HORSE is a product of the grasslands and grass is therefore his natural feed.

Only after he had ventured away from the forest, where he was accustomed to living on the twigs of shrubs and trees, and became adapted to living on the grass of the plains did the horse develop from the dog-sized creature that was his progenitor to the princely animal that he is today.

The small wild horse of Asia and the so-called wild, or feral, horse of our western plains still live entirely on grass. Often they refuse, when captured, to change their dietary habits to include any form of concentrate feeds. Only in the process of domestication has the horse been induced to adapt himself also to diets that may include all kinds of feeds supplied ( according to the fancy of the feeder or the exigencies of circumstances) in the form of grains, seeds, roots, and tubers; animal products such as milk, meat, eggs. and bonemeal; byproducts of the mill, brewery, and distillery; cannery wastes and cull fruits; seaweeds, fish meal, and some fish oils. Even wood pulp and treated sawdust have been tried.

Such feeds have been used to replace varying proportions of the natural grass ration, sometimes because of convenience and availability and sometimes because of economy in utilizing materials that perhaps otherwise would be wasted but oftener because a substitution of other feeds for part of an all-grass ration makes for better development and more efficient use of the horse.

The grassland crops, pasture herb-ages and cured hays, and fodder and straw constitute most of that class of feeds commonly called roughages.

No one feed is as complete a ration for the horse as good pasture grass, or good grass or legume hay of the current season's crop. But rations composed of roughages alone are usually less efficient than rations made up of combinations of roughage feeds and concentrate feeds, especially for horses at work and for the growing young. Nevertheless, the roughage feeds have special functions in the equine ration apart from their value as sources of energy and protein. They are important sources of the vitamins and minerals that are associated with green leaves, and they serve further to satisfy whatever may be the needs of the horse for bulk.

The green leaves of growing pasture plants are rich sources of carotene, which is converted into vitamin A in the animal body. But when green pasture is not available, the ordinary horse ration is often deficient in vitamin A activity because of the use of poor or old hay. In a study of the minimum carotene and vitamin A requirements of the horse, a group of investigators in California produced symptoms of acute vitamin A deficiency, in which the symptoms were night blindness, rough coat, reproductive failure, respiratory difficulties, and, eventually, death.

But one of the more commonly observed symptoms of a subacute vitamin A deficiency occurring spontaneously from the use of carotene-deficient rations is faulty hoof development. Some observers believe that vitamin A deficiency also constitutes one factor in the production of many of the common unsoundnesses of horses, for example, stringhalt, roaring, ring bones, side bones, arthritis, and navicular disease. Others have associated vitamin A deficiency with respiratory infections and with the occurrence of urinary calculi. The poor condition seen frequently in horses kept for long periods on restricted diets has often been attributed to vitamin A deficiency and has been reported to be relieved by injecting or feeding vitamin A in some form.

The minimum daily requirement of the mature horse has been estimated at about 2.0 to 2.4 micrograms of vitamin A or 9 to 14 micrograms of carotene per pound of body weight. Thus, to assure freedom from symptoms of vitamin A deficiency, the daily ration of the 1,000-pound horse should provide at least 15 milligrams of carotene, an amount that can easily be supplied by one-half pound of fresh, young, pasture grass, or by a similar quantity of carrots; by 1 pound of average No. 1 alfalfa hay or 2 pounds of average No. 1 timothy hay; by one-fourth pound of dehydrated alfalfa leaf meal, or by 1 to 3 pounds of silage. Four or five times that allowance should be made for breeding animals. A still more generous allowance is advisable for growing colts.

Animals on pasture depend on the action of the sun's rays on their skin for the manufacture of their own vitamin D because green pasture plants have practically no vitamin D activity, either fresh or as silage. When cut for hay, however, the forage achieves a vitamin D potency during exposure to the sun while curing. Artificially dried hay is high in carotene but quite low in vitamin D. With the exception of the sun-cured hays, the common horse feeds are lacking in this factor.

Information regarding the vitamin D requirements of horses at different ages and the interrelation of this vitamin with the horse's utilization of calcium and phosphorus is badly needed. The sun-cured hays usually supply adequate amounts for the adult animal, but the requirements of the young, growing animal are considerably greater than those of the adult. Unless the young animal has access to ample sunshine, he may be deficient in the vitamin D needed for normal calcification of growing bone. In this case he will probably show some of the manifestations of rickets. Supplementary vitamin D can be supplied in the form of one of the readily available vitamin D concentrates.

The recent investigations concerning the B vitamin requirements of the horse have indicated that riboflavin and possibly pantothenic acid also are required preformed in the horse ration. The investigators have concluded that the riboflavin requirements of the horse are of the same order as those of man; that is, about 20 micrograms daily per pound of body weight. The forage feeds are generally much richer in riboflavin than the grains. In order to provide 20 milligrams (which is the probable daily requirement of a 1,000-pound horse) from oats or barley, 33 pounds of grain would be required but this same amount of the vitamin can be obtained from about 2 1/2 pounds of good sun-cured alfalfa hay or 5 pounds of average timothy hay.

Some research carried out in the Veterinary Research Laboratory of the United States Army has directed attention to an apparent relation between riboflavin deficiency and the occurrence of periodic ophthalmia. The workers reported that daily doses of 40 milligrams per horse prevented the development of the condition although it was not effective as a cure.

Feeds such as the grains and the protein concentrates may be depended upon generally to supply ample phosphorus in the horse ration, but the forages are the important sources of calcium and of many of the so-called trace minerals. The forages, if they are grown on good soil, may also supply adequate phosphorus for the horse, but if they are produced on phosphorus-deficient soil they are usually too low in phosphorus for safe use as the sole source of supply.