190 BETTER DAIRY FARMING 



another feed. Thus, we speak of differences in quality of proteins, 

 meaning that one may have a higher feeding value than another. 

 Though we know that these differences occur, we do not yet know 

 how to classify the feeds on this basis, so we use the general term, 

 crude protein, or simply protein, to cover all the proteins. How- 

 ever, we do know that certain combinations make for high quality 

 — for example, a leafy roughage combined with cereal grains. 



316. Carbohydrates. — These comprise substances which are 

 familiar to all, namely, sugars, starches, and celluloses. They are 

 of only limited occurrence in the animal body, but occur in plants 

 in a larger proportion than do any of the other chemical com- 

 pounds. Cellulose forms the framework of plants and the protec- 

 tive coating of seeds, while starches and to a less extent sugars 

 constitute the reserve material which furnishes energy for growth 

 and for building new tissue. 



Over one-third of the dry matter of milk consists of the carbo- 

 hydrate, lactose. Thus in milk production the carbohydrates of 

 the feed may serve not only to furnish energy for the process but 

 also as a source of one of the constituents of the product. 



There are two other terms used in connection with carbohydrates 

 which we should know, namely, crude fiber and nitrogen free 

 extract (X.F.E.). These terms do not represent distinct chemical 

 groups but rather classes into which all carbohydrates have been 

 divided, using feeding value as a basis. Crude fiber is what is left 

 of the carbohydrates of a feed after the removal of the more sol- 

 uble ones by the use of certain chemical agents. This residue is 

 woody in nature and consists principally of the more complex 

 celluloses. The remaining carbohydrates — the sugars, starches, 

 and some of the celluloses — form the group known as the nitrogen 

 free extract. 



317. Fats. — These compounds occur in all parts of the animal 

 body as fatty tissues. In plants they occur especially in the seed 

 portion, and many seeds, such as the seeds of cotton and flax, are 

 very rich in them. Like the carbohydrates, the fats of the feed 

 serve as sources of energy. The fat which is stored in the animal 

 body constitutes the energy reserve to be drawn on in time of need. 



