PART I PRINCIPLES OF FEEDING FARM ANIMALS

CHAPTER I

THE COMPOSITION OF FEEDING STUFFS The feeding stuffs used for the nutrition of farm animals are, as a general rule, of vegetable origin. They are either farm crops grown especially for this purpose, or are by-products from manufacturing processes in which farm crops furnish the raw materials. It will be well, therefore, to examine into the composition of plants at the outset, in order that the discussions given in the following pages relative to the feeding of farm animals and problems connected therewith may be clearly understood.

Chemical Elements.--Plants are composed of an immense number of different compounds; some of these are present in large proportions, others in only small amounts. When these compounds are separated into their ultimate constituents we find that they contain a relatively small number of substances which, according to our present knowledge, cannot be further subdivided. These substances are known as elements. About a dozen of the elements are absolutely necessary to plant life, and no plant can grow in the absence of one or more of them. These so-called essential elements

are:

Carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium, iron, fluorin, and iodin.

A few other elements may not be essential to plant growth, but are always present in plants. These are:

Sodium, chlorin, silicon, and manganese.

The first group of elements, in fact the first six of them, make up the bulk of all plant materials; over 95 per cent of the weight of most plants and feeding stuffs is composed of these few elements. But the other essential elements, although present in small amounts, are equally important, since plants cannot grow to maturity if any of them be lacking in the soil or not available to the plant.

Groups of Components in Feeds.The elements given in the preceding paragraph are present in plants in chemical combinations with each other, forming in some cases very complex substances whose exact composition has not yet been ascertained. For our present purpose they may, however, be conveniently considered as belonging to a few groups of substances which can be readily determined by chemists. These groups of components are separated in the customary chemical analysis of feeding stuffs, and the percentage quantities present in each are ascertained. For the purposes of chemical analysis and for our discussions we may thus consider plant materials composed of,

I. Water.

II. Dry substance. The dry substance of plants is of either (1) mineral or (2) socalled organic origin. The former components are known as mineral matter or ash; while the organic matter is composed of the following groups of substances: Protein, fat, nitrogen-free extract, and fiber. The last two belong to a group of substances known as carbohydrates.

The schedule given below will help to make clear these various groups of plant components:

Plants contain

Composed of the elements I. Water..

Oxygen, hydrogen.

(Potassium, sodium, calcium, II, Dry substance: 1. Mineral matter (ash).

magnesium, sulfur, chlorin, iron, phosphorus,

silicon, etc.

Carbon, oxygen, hydrogen, 2. Protein.....

nitrogen, sulfur (and

sometimes phosphorus). 3. Fat... 4. Nitrogen-free extract Carbon, oxygen, hydrogen. 5. Fiber.

COMPOSITION OF PLANTS Water is found in all plants and plant materials, ranging in amount from 5 per cent to 95 per cent in extreme cases. Some factory by-products which have been artificially dried contain less than 10 per cent, in some cases as low as 5 per cent of water. Hay and dry coarse feeds generally contain from 10 to 20 per cent, while corn fodder (stover) and some kinds of hay, as alfalfa, will occasionally contain as much as 30 per cent of water when imperfectly cured or exposed to damp or rainy weather. The cereals and most concentrated feeds contain about 12 per cent water; green forage contains from 70 to 90 per cent; silage 60 to 80 per cent; root crops, beet pulp, and wet brewers' grains, 80 to 90 per cent; in case of turnips and some vegetables, as pumpkins, the water content may reach even 93 to 95 per cent (Fig. 1).

A knowledge of the amount of water in a feeding stuff is important, both because its value for the nutrition of farm animals is largely dependent thereon and because its keeping quality is affected thereby. A high water content renders plant materials liable to decomposition through the growth of bacteria and molds.

Water is the vehicle by which nutrients in both plants and animals are transported from one part to another. Plants absorb it from the soil through their roots, and with it take up mineral matter held in solution in the soil water. The quantity of water

thus taken up by plants is very large, and this is partly retained in the cells and the sap of the plants, and partly again evaporated through the leaves. For every pound of dry substance in the plant it has been found that about 400 pounds of water are required, on the average, the exact figure varying from below 300 to over 1000 pounds, according to the character of the soil and the crop.

Dry Substance. The components of the dry substance of plants considered in the following pages are: Mineral matter or ash, protein, fat, nitrogen-free extract, and fiber.

Mineral matter in plants is derived from the soil through the root system. This is the portion of the plant which remains as ashes after combustion. It is composed of the elements already given and, in addition, of many elements that happen to be present

in the soil where the plant grew. The elements found in the mineral matter are present in one or two forms: Either in inorganic form, as sulfates, phosphates, nitrates, chlorides, or silicates, combined with bases, like potassium, sodium, calcium, magnesium, and iron; or in organic form, as constituents of organic compounds. Especially in the case of seeds of plants the ash materials are present largely in the latter form.

Ordinary feeding stuffs contain, as a rule, only relatively small amounts of mineral matter, viz.: Less than 5 per cent, except in the case of some factory by-products and dry forage, in which the ash content may go even above 10 per cent. Leafy plants contain

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 ALFALFA HAY COTTON-SEED MEAL CLOVER HAY WHEAT BRAN LINSEED MEAL DRIED BEET PULP TIMOTHY HAY DRIED BREWERS' GRAINSI OATS CORN GLUTEN FEED POTATOES

FIG. 2.-Mineral matter in a ton of common feeds, in pounds. relatively large percentages of ash, like all parts of plants in which a considerable evaporation of water takes place. On the other hand, by-products in manufacturing processes where the raw materials are treated with large quantities of water, as gluten feed, brewers' grains, beet pulp, etc., have comparatively low ash contents (Fig. 2).

Protein is a general name for nitrogenous organic compounds of a very complex chemical structure. They contain carbon, oxygen, hydrogen, and nitrogen, with a small percentage of sulfur and, in some cases, phosphorus. The name protein was given to these substances by Mulder, a German chemist, and means the first or the most important. This term is justified from a physiological point of view, inasmuch as protein is absolutely essential to animal life, for the formation of muscle, body fluids and other nitrogenous body substances, as well as for the continued exercise of vital functions.

The protein substances are characterized by the fact that all contain the element nitrogen, which is not found in the other groups

16)

of organic plant substances. It was formerly believed that all proteins contain about 16 per cent nitrogen, and, since this element can be readily determined by the chemist, the content of protein in a substance was obtained by multiplying the nitrogen content by 10, or 6.25. Later investigations showed that the different protein substances vary considerably in chemical composition, and that the percentage of nitrogen they contain may range from 15 to over 19 per cent. Hence, the factor 6.25 is often not correct, but it is generally applied, since our knowledge of the composition of pure proteins from different sources is still incomplete. We shall, therefore, continue the use of the factor 6.25 in this book until chemists have agreed on specific factors to be used in the case of plant materials and feeding stuffs of different origin.

Besides nitrogen, proteins contain between 50 and 55 per cent of carbon, 6 to 7 per cent hydrogen, 20 to 24 per cent oxygen, 0.3 to 2.3 per cent sulfur; the phosphorus content of the proteins in which this element is present ranges between 0.4 and 0.9 per cent. The average composition of protein substances may be given as follows: Carbon, 53 per cent.

Nitrogen, 16 per cent.
Hydrogen, 7 per cent.

Sulfur, 2 per cent. Oxygen, 22 per cent. The proteins form a most important group of nutrients, since they furnish the materials for building up body tissues and fluids; other nutrients cannot take their place for this purpose. We shall see, however, that protein may also serve other purposes than to furnish material for tissue building when necessary, viz.: To supply energy that may be used for maintaining body heat, for performing work, or for storage as body fat.

Classification of Proteins.—Protein substances are generally classified as (1) simple, (2) conjugated, and (3) derived proteins.