Forage for Livestock

PLUS AND MINUS: AN OVER-ALL VIEW

N. R. Ellis, L. A. Moore, M. A. Hein

ALL CLASSES of domestic animals are alike in that they eat forage in some form. They differ, though, in the extent of their use of grass and such crops. Dog foods may contain small amounts of alfalfa leaf meal; poultry diets include forage meals to supply vitamins, minerals, and proteins, and increasing emphasis is placed on pasturage for poultry flocks; swine consume much more herbage; and horses, goats, sheep, and dairy and beef cattle sometimes get all their feed from forage.

This difference rests on differences in their digestive systems and ability to handle the bulky forages, which have a relatively high content of celluloses, lignins, and other carbohydrate materials that are not readily attacked by the enzymes of the digestive tract. Micro-organisms in the digestive tracts Of cattle, sheep, goats, and horses secrete enzymes that can break down celluloses, but the lignins seem to be left relatively untouched.

Also, quite apart from the matter of bulkiness, the cell walls in the plants resist digestion, and so affect the ability of swine and poultry, for example, to make full use of the proteins, fats, minerals, and even the vitamin factors within the cells. In other words, horses, cattle, and sheep have special advantages in utilization of forages not shared by single-stomach animals such as swine.

The first need of animal life is for heat and energy, and the central chemical element is carbon. Carbon occurs in starches, sugars, and other carbohydrates, fats and oils, proteins, and even in plant pigments and the vitamin compounds. Depending on the animal's digestive capacity, the forages are therefore prime sources of energy by which to maintain life, grow, secrete milk, perform work, and reproduce.

Protein is next. Growing animals, which are building their muscular structure, need more protein than mature, resting animals. Likewise the growth of wool, the formation of milk, and the development of the fetus call for a relatively high intake of protein. These varying requirements for protein (which cut across the varying percentages of proteins in forages) produce a situation in which the animal may sometimes fail to eat sufficient forage to obtain enough protein to meet the requirements. In such a case retardation must result, whether it be production of wool or of the muscle structure.

Proteins are complex substances that are built up from amino acids. The twenty-odd amino acids are the channels through which food protein passes in the body in the transformation to the proteins formed by the animal and built into muscular framework, milk, eggs, wool, hair. About 10 of the amino acids known to science are essential to man, and probably to poultry and swine. Apparently the micro-organisms that grow in the rumen of cattle and sheep can build up these essential amino acids to the benefit of the host. Accordingly, the amino-acid make-up or quality of the protein in forages is not highly important to cattle and sheep. Poultry and swine, although quality of protein is important to them, do not subsist on forage to such an extent as to make the matter of much importance.

The mineral elements generally considered essential to animal life include calcium, phosphorus, magnesium, sodium, chlorine, iodine, iron, copper, manganese, sulfur, zinc, potassium, and cobalt. The actual needs of the several classes of farm animals for a number of the elements have not been demonstrated for a certainty, however, because of their occurrence in animal tissues and in feeds in very small amounts.

The content of the more common minerals in the body can be illustrated by data on steers. Expressed as percentages of the fat-free body, the approximate figures are: Calcium, 1.33; phosphorus, 0.74; potassium, 0.19; sodium, 0.16; sulfur, 0.15; chlorine, 0.11; magnesium, 0.41; iron, 0.013.

From the standpoint of forages and their supply of these eight mineral elements, the principal concern in animal feeding is in calcium, phosphorus, sodium, and chlorine. Skeletal growth depends largely on an adequate supply of calcium and phosphorus. Sodium and chlorine, which together form common salt, are constituent parts of body tissues and fluids. Iron, cobalt, and copper are generally associated because of their roles in blood formation. Iodine is needed in the normal functioning of the thyroid gland. Other than the needs of poultry for manganese, little is known about the functions and requirements for manganese and zinc in other livestock. On the other hand, too much of certain substances selenium and fluorine, for instance, can have harmful effects.

Even greater extremes exist in the requirements of different classes of animals for particular vitamins. Problems also arise from the differences in the disappearance of the vitamins in successive stages of ripening of the forage and in the ways the harvested crop is preserved and stored.

Only two vitamins, A and D, are known to be required by cattle, sheep, and goats. For horses, it appears that riboflavin and pantothenic acid need to be added to the list. For swine, thiamine, nicotinic acid, pyridoxine, and choline are certainly needed. The list for poultry must also include biotin, vitamin E, and vitamin K. These differences, as they concern the so-called vitamin-B-complex factors, are related largely or entirely to the activities of the micro-organisms in the digestive tracts of animals.

General Feeding Values

It follows from the long history of the reliance of different livestock on grassland crops for their food supply that forages in general must supply these necessary feed nutrients. In the unraveling of the details about individual items, it has become evident that the exceptions to this generalization account for much of the failure to obtain best performance in our livestock. In many parts of the world in many ages, people have learned to avoid troubles with their flocks by moving them from one area to another. Restrictions of feed supplies in one way or another have brought about conditions conducive to many of the nutritional deficiencies that confront us today. In the main, grassland crops do supply those nutrients that animals require within the limits, of course, to which different kinds of livestock are naturally adapted to utilize forage.

The energy supply on which life so heavily depends can be obtained readily enough from forages, providing a few conditions are met. These include an adequate supply, reasonable palatability and digestibility, and adequate quality. A cow that has to search over 40 acres of range for a few pounds of grass may not be able to obtain the needed energy to maintain weight. Likewise, consumption of 30 pounds of dry forage of low digestibility may not support life so well as 15 pounds of a highly digestible forage.

This difference in feeding value is determined markedly by seasonal and climatic factors. Furthermore, it is often more accentuated on ranges than in pastures. The growth of most range grasses in the South, for example, revives early in the spring, and the plants grow and mature comparatively rapidly. The peak in their feeding value is passed even by the beginning of summer. In the drier sections of the West, somewhat similar conditions exist with slower rates of growth and later maturity in the northern zones. Thus a wide difference in feeding value may exist on a given range at different times of the year.

On the average, cattle and sheep can digest and assimilate approximately 60 pounds of feed nutrients for every 100 pounds of dry matter in forages. In other words, 100 pounds of dry matter yield about 60 pounds of total digestible nutrients.

Some variations from this figure are of interest. For example, young plant growth generally yields more than older, more mature growth. Pasturage generally yields 3 or 4 pounds above the 60-pound average; hays and silages yield 2 or 3 pounds less. The approximate equality of hays and silages and the near 10-percent superiority of tender green material in total digestible nutrients is borne out, in the usual case, in actual production of livestock and livestock products.

A 600-pound steer that gains an average of 1.4 pounds daily needs about 8.5 pounds of total digestible nutrients. In terms of timothy hay with a dry-matter content of 90 percent, this is 16.3 pounds. On pasture, the steer must eat nearly 67 pounds when the dry matter is as low as 20 percent.

That is not to say, however, that wide differences in available energy or total digestible nutrients do not occur within classes of forages, whether pasture, silage, or hay. The studies of E. W. Crampton and others in eastern Canada give evidence that the digestibility of the dry matter of pasture herbage may drop from a high value of 80 percent in the early spring to 60 percent and less in midsummer. Significant changes occur in chemical composition, of course.

But Dr. Crampton's work, which discloses the lack of positive and high correlations between the data on composition and digestibility, shows that we cannot trust ordinary data on chemical composition as indices of digestibility and ( still more important) of feeding value. From the practical, economic standpoint, the results emphasize the great need for further studies to find some constituent that can be determined chemically and that can give more reliable information on the digestibility of forages.

These studies on composition and feeding values suggest, however, that increasing the ratio of leaves to stems may be associated fairly well with increasing the digestibility. Possibly not enough attention has been given to the usefulness of forages with a maximum leaf content. We have realized for some time that leafy hays were much more valuable than those with a high content of stems. Much of this advantage has been attributed to the content of protein, minerals, and vitamins. Typical figures on the digestible nutrients of alfalfa leaves (dry-matter basis) may reach or surpass 65 percent and for alfalfa stems may fall to 46 percent or less. It thus appears that available energy may be the more important factor in many instances.

It has been estimated that forages supply approximately 60 percent of the protein consumed by livestock. Of that amount, pasturage and range supplies about two thirds; hays, silages, and other harvested forages supply the other third. The other 40 percent of protein consumed is obtained from the concentrate feeds.