FEEDING OF FARM STOCK. 189 



the soil, together with whatever sand and dust that has 

 gotten into the feed. By protein he means the amount of 

 various nitrogenous substances. These are found by deter- 

 mining the nitrogen and multiplying the amount by six 

 and one quarter. By carbohydrates he means the starch, 

 sugar, gums, crude fiber, organic acids and a few other sub- 

 stances taken collectively. By ether extract or fat he 

 means the fats, oils, and waxy substances of the feed. The 

 common name for these substances is fat, although the term 

 ether extract is frequently used because in the analysis 

 they are dissolved from the feed with ether. These five 

 different classes of substances or nutrients as they are 

 called are expressed percentagely and the results of analysis 

 indicate the number of pounds of each that are found in 

 100 pounds of the given feed. It is only to three of these 

 substances, the protein, fat and carbohydrates, that the 

 feeder need attach any importance. The water is impor- 

 tant only in showing how much of it is being bought in a 

 given feed. Water is cheap, and other things being equal, 

 moist feeds should be correspondingly low in price. The 

 ash is unimportant because all feeds contain an abundance 

 of it for the needs of the animal body. 



COMPOSITION AND DIGESTIBILITY OF FEEDS. 



Tables showing the amounts of the different classes of 

 substances just noted are called "composition tables," be- 

 cause they tell us of what a feed is composed. These tables 

 although very important fail to tell us the whole story, 

 because they do not show what proportion of the nutrients 

 in a given feed the animal is able to digest and make use 

 of. It is at this point that the feeder and physiologist 

 come to the aid of the chemist and help to make another 

 set of tables which are called "tables of digestibility." By 

 actual feeding trials in which a careful record of the 

 weights of the animal and the amounts of feed and water 

 given is kept, together with a chemical analysis of the feed 

 and of the excrements and urine of the animal, the proper- 



