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pentosans are widely distributed in plants, and make up a considerable proportion of the nitrogen-free extract of many plants. Hay from grasses contains about 20 per cent of pentosans; gluten feed, 17 per cent; dried brewers' grains and wheat bran, 24 per cent; clover, 10 per cent; cereal straw, 22 per cent; oil meal and dried distillers' grains, 13 per cent.

The best known substances of this group are araban, found in beet pulp, cherrygum, etc., and xylan or wood gum, found in wood and straw.

The pectin bodies occur especially in unripe fruits; these substances are responsible for the jellying of fruit juices, which depends upon pectin taking up water during the boiling of the fruit,

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Fig. 4.–Fiber in plant materials, in per cent. gelatinous substances being formed known as pectoses or pectic acids. The mucilaginous substances of flaxseed and seeds or roots of some other plants belong to this group; these substances do not, however, possess the importance that is attached to the preceding three groups of compounds, starch, sugar and pentosans.

Fiber called crude fiber or woody fiber by some authors) makes up the cell walls of the plants and is largely composed of cellulose. So-called incrusting substances (lignin and cutin) are always present, especially in tough, woody plant materials, like husk, hulls, seed-coats, overripe hay and straw, which contain considerable proportions of these substances in the fiber. Fiber is more resistant to the action of solvents and digestive fluids than other groups of plant materials. It is attacked by bacteria and possibly by special ferments in the intestinal tract of herbivorous animals. By this decomposition marsh gas and other gases are formed, and also organic acids, like acetic and butyric acids. Since straw is very high in fiber, and ruminants, like steers, sheep, and goats, can subsist for a long time on coarse straw only, we are justified in concluding that this substance possesses a certain nutritive value, although authorities differ as to how much value shall be ascribed to the digestible portion of cellulose.

Plants increase in their contents of fiber toward maturity as the stems become coarse and tough; hence their digestibility decreases during the latter stages of plant growth (p. 58). The following approximate amounts of fiber are found in different classes of feeding stuffs :

Buckwheat hulls, buckwheat straw, and flax shives, 45 per cent; straw of cereals, 40 per cent; hay from different grasses or legumes, 20 to 35 per cent; cereals, 0.2 per cent (hulled rice) to 10.8 per cent (oats); roots and tubers, 0.4 to 2.2 per cent; concentrated feeds, 0.9 to 30 per cent, generally, however, less than 20 per cent (Fig. ).

A high fiber content indicates that a feed is of relatively low value for stock feeding, and vice versa. The figures for this component, with those for protein and fat, are, therefore, of the greatest assistance to feed buyers in judging the value of manufactured and other feeds.

Chemical Analyses of Feeding Stuffs.—The following components are determined by the chemist in the ordinary analysis of feeding stuffs: Water (often called moisture), protein, fat, fiber, and ash; the difference between 100 and the sum of percentages of these various components obtained in the analysis is known as nitrogen-free extract (starch, sugar, pentosans, organic acids, etc.).

Methods of Chemical Analysis.-—The outline of the common method adopted in chemical laboratories in the analysis of feeding stuffs given below will be of value to den by enabling them to better understand data and discussions relating to the chemical composition of feeding stuffs (Fig. 5).

a. Moisture (water) is determined by heating a small portion (generally 2 grams)? of the carefully.sampled and finely-divided feeding stuff in a steam-bath or water oven at 100° C. for two to five hours, till it no longer loses weight. After cooling in a desiccator, it is weighed carefully on a chemical balance and the percentage loss calculated on the original weight is taken to represent moisture. Volatile organic substances sometimes present in minute amounts in plant materials would also be included in this loss. In the case of some feeding stuffs containing fats that take up oxygen, as corn, flaxseed, and other oil-bearing seeds, the material must be heated in a current of hydrogen or other inert gas, so as to prevent oxidation and a resulting increase in weight during the drying, which would give too low a moisture content.

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b. Fat.—The residue from the preceding determination is extracted with anhydrous sulfuric ether in a suitable apparatus for a considerable period of time, generally 16 hours, till the fat has been completely dissolved. The ether is distilled off and the residue dried at 100 ° C. and weighed. As previously stated, the ether extract, in the case of roughage and some other feeds, contains considerable impurities, as chlorophyl, wax, and resins.

c. Protein is obtained by multiplying the total nitrogen by 6.25 (see p. 9), the nitrogen being determined by the Kjeldahl method, so called after the inventor, a Danish chemist. In this method a small portion of the feed (generally 1 gram) is heated with 20 c.c. sulfuric acid till the organic matter has been completely decomposed and the nitrogen has been changed into ammonium sulfate. This is dissolved in distilled water,

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Fig. 5.- View of a chemical laboratory for analysis of feeding stuffs and other agricultural

products. (Wisconsin Station.)

and 50 c.c. of a concentrated soda solution are added, the flask being connected with a distillation apparatus and heat applied. A certain quantity of standard hydrochloric acid solution, more than sufficient to neutralize the ammonia obtained in the oxidation of the protein, has been previously added in the receiving flask, and the distillation is now continued till all ammonia has been distilled over. The excess of acid in the receiving flask is then accurately titrated back (neutralized), and from the volume of acid used the amount of nitrogen in the sample is obtained. This is calculated in percentage of the amount of sample weighed out, and by multiplying by 6.25 the percentage of protein contained in the sample is obtained.

d. Fiber is determined in the residue from the fat extraction by boiling first with 200 c.c. of a 1.25 per cent sulfuric acid solution and then with 200 c.c. of a soda solution of the same strength. After filtering, drying, and weighing, the residue is ignited, and the loss in weight, calculated on the amount of the sample originally weighed out, shows the percentage of fiber in the feed. This method, which is known as the Weende method gives pure cellulose or woody fiber, with some impurities like pentosans, incrusting substances (lignin, cutin), and certain insoluble proteins. The method does not give very satisfactory results, and is only used for want of some better method of arriving at the amount of fiber present in feeding stuffs.

e. Ash or mineral matter is obtained by igniting at a low red heat 2 grams of the sample and weighing the residue after cooling in a desiccator. The crude ash thus obtained generally contains some free carbon, as well as carbonates and sulfates formed by oxidation of organic components of plant materials. It is sometimes purified by treatment with distilled water, and the amount thus found is given as pure ash.

f. Nitrogen-free extract is obtained by subtracting the sum of the percentages of the preceding components from 100. it includes chiefly starch, sugar, pentosans, and organic acids (p. 13). The amounts of the first three components are also sometimes determined separately by wellknown methods of analysis that are of interest mainly to chemists.

The example given below will show the customary form of reporting analyses of feeding stuffs.

Chemical Analysis of Timothy Hay

Moisture
Crude protein
Fat
Fiber
Nitrogen-free extract
Ash

Per cent
13.2
5.9
2.5
29.0
45.0
4.4

100.0 QUESTIONS 1. Name the elements essential to plant growth; also some others that

are always present in plants. 2. What are the groups of plant components determined in ordinary chemical

analyses ? 3. Give the main characteristics of each one of these components. 4. What is protein, nitrogen-free extract, carbohydrates ? 5. State the difference in the chemical composition of these substances. 6. Give the ordinary form of reporting a chemical analysis of a feeding

stuff.

* For complete directions for making chemical analyses of feeding stuffs and other agricultural products, see Official and Provisional Methods of Analysis, Association of Official Agricultural Chemists, Bureau of Chemistry, U. S. Department of Agriculture, Bulletin 107 (Revised), Washington, 1912.

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CHAPTER II

THE COMPOSITION OF ANIMALS We find, in general, similar substances in the animal body as in plants, but the relation between the different groups of components differs, and some substances found in animals do not exist in plants, or differ in their properties from the corresponding plant constituents. Animals are composed of water, protein bodies, fat and mineral matter; the protein, or protein and fat, make up the largest proportions of the dry matter of animals, while carbohydrates are present in only small amounts. We have seen that the dry matter of plants, on the other hand, is largely composed of carbohydrates, and that protein is, as a rule, present in relatively small amounts.

The composition of different farm animals varies according to age and body condition, especially the amount of fat which they carry. The classic experiments of Lawes and Gilbert which were conducted about 1850 at the Rothamsted Experiment Station, England, furnished the first accurate information on this point; their findings have been corroborated during later years by investigations at the Maine and Missouri Experiment Stations and elsewhere. The following summary table shows the percentage composition of live animals, less contents of stomach and intestines:

Composition of Live Animals, in Per Cent. (Lawes and Gilbert.)

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The figures given in the table show that the fatter an animal is, the less water, protein, and ash will it contain; also, that the percentage of fat in the body of a steer may range from at least 8 to 30 per cent, that in a sheep from 10 to 41 per cent, and that in a hog

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