40 



MANUAL OF FABM ANIMALS 



Fig. 26. — Champion English Shire 

 Stallion "Mazemore Harold." 



essential to the animal body, and second, the percentage of pro- 

 tein is relatively small in most plants. Like the other nutrients, 



the protein group contains 

 carbon, hydrogen, and oxygen, 

 and in addition it also con- 

 tains nitrogen, which is the 

 characteristic element of the 

 entire group. It is on the 

 element nitrogen that the im- 

 portance of this group de- 

 pends. Protein enters largely 

 into the composition of the 

 bones, muscle, lean meat, 

 white of egg, and the curd of 

 milk. The only source from 

 which the animals can procure this protein is the protein of 

 the food. 



The amount of digestible protein in various foods varies 

 within rather wide limits, corn containing only 8 per cent, while 

 cotton-seed meal runs as high as 32 per cent, but the larger 

 number of food materials contain rather small amounts of pro- 

 tein. There are comparatively few foods that are relatively 

 rich in protein. The value of the food turns very largely on 

 the protein which it contains. Protein is not, however, as 

 digestible as some of the other nutrients. 



Carbohydrates. — There are two sub-groups of carbohydrates 

 — nitrogen-free extract, and crude fiber. The carbohydrate 

 group contains carbon, hydrogen, and oxygen, but no nitrogen. 

 The nitrogen-free extract is composed largely of starches and 

 sugars, and constitutes the larger part of the dry-matter of most 

 plants. Starch alone forms as much as 75 per cent of the dry- 

 matter of corn, wheat, potatoes, and some other foods. It is 

 easily digested, more so than any of the other three constituents, 

 and therefore foods rich in nitrogen-free extract are ordinarily 



