154 FIRST PRINCIPLES OF AGRICULTURE. 



CHAPTER XIII. 



The Digestibility of Fodders and Feeds ; Feeding Standards ; 

 Nutritive Ratio ; The Exchange of Farm Products for Con- 

 centrated Feeds. 



THE nourishment that may be derived from any food 

 depends not only upon its composition in reference to 

 the specific food substances that it contains, but also 

 upon the amount of these that may be digested by the 

 animal. 



Digestibility of Fodders and Feeds. Pure nu- 

 trients, as albumen, starch, or fat, are regarded as 

 entirely digestible. These nutrients, however, do not 

 exist in the various feeding materials in a pure state. 

 They are associated with substances that are indigesti- 

 ble, or that hinder their digestibility; hence the entire 

 digestibility of a food is governed both by the purity 

 of the nutrients which it contains, and by the ab- 

 sence of those compounds which prevent the complete 

 action of the digestive fluids. 



Seeds of plants, as a rule, contain matter of a readily 

 digestible character ; that is, the nutrients contained in 

 them are relatively pure : but they are, in many cases, 

 enclosed in a hard shell, and, particularly if swallowed 

 whole, resist the action of the digestive processes, thus 

 preventing the digestion of the entire seed. In the 



