16 



PRINCIPLES OF FEEDING FARM ANIMALS 



Table 4. — Percentages of Nitrogen-free Extract in the 

 Different Classes of Feedingstuffs ^ 



Crude Fiber. — Crude fiber is the tough, woody, fibrous 

 portion of plants. It is made up principally of cellulose 

 and other similar substances, together with some i)entosans. 

 Cellulose is composed of the elements carbon, hydrogen, 

 and oxygen, and is one of the complex carl)ohydrates. It 

 forms the groundwork of all vegetable tissues, the walls 

 of all plant cells consisting of cellulose. Thus it is found 

 in all parts of the plant as an essential constituent of every 

 plant cell. It is seldom found pure in nature, except in 

 the young and tender parts of plants, but usually it is im- 

 pregnated more or less with lignin, which is a carbohydrate 

 that is similar to, but harder and tougher than, cellulose. 



The proportion of crude filler in plants varies greatly 

 with the species, size, and degree of maturity of the plant. 

 As a rule, large plants contain more than small plants, 

 and mature plants contain more than immature ones. In 

 general, the hardness and toughness of large or mature 

 plants are due to their increased content of crude fiber. Also 

 the proportions of crude fiber in the different parts of the 



1 These values represent the upper and lower limits of the average con- 

 tent of nitrogen-free extract of the common feedingstuffs included under each 

 class. 



