THE FEEDING OF ANIMALS 277 



builds tissues; that is, cartilage, tendons, and lean meat or 

 muscle. Besides this, it enters into the casein and albumen 

 in milk and seems to be a stimulator of milk and egg pro- 

 duction. When necessary the body uses protein to make fat 

 and to furnish heat to keep the body warm and energy with 

 which to move it, but when an animal is properly fed the pro- 

 tein is not much used for such purposes. 



Crude Fibre is the tough, woody part of plants. It is com- 

 posed mainly of cellulose and is not easily digested. Cellulose 

 is the substance that makes the walls of cells and has the 

 same composition as starch, but is not nearly as easily di- 

 gested. Any food which is composed mainly of stems or has 

 many hulls in it will contain a large percentage of crude fibre 

 and will not be first-class feed. Grains have much less crude 

 fibre than hay and fodder. For example, wheat contains 

 about 1.8 per cent, and clover hay about 24.8 per cent, 

 crude fibre. 



All feeds contain some oil or fat. There is more fat in 

 feeds derived from seeds like corn, oats, or cotton-seed than 

 there is in hay. In the process of analysis the fat is dissolved 

 out with ether, and for this reason fat is often referred to in 

 tables of food composition as ether extract. Fat is composed 

 of carbon, hydrogen, and oxygen, and serves the same pur- 

 pose in the body as the nitrogen-free extract. 



The nitrogen-free extract is what is left after the crude fibre, 

 fat, protein, and ash have been removed. It, too, is com- 

 posed of carbon, hydrogen, and oxygen. According as these 

 elements are united we have starch, sugar, gum, and other 

 substances. Nitrogen-free extract and crude fibre are often 

 spoken of as carbohydrates. The carbohydrates and fats are 

 the fuel of the body. By the process of digestion they are 



