278 AGRICULTURE FOR COMMON SCHOOLS 



changed just as wood or coal is changed in the fire and in the 

 same way give heat. This heat furnishes warmth to the body 

 and also energy for the action of the body. The carbo- 

 hydrates and fat also form fat in the animal body, and from 

 these comes the fat found in milk. 



Nearly all feeds have a large per cent, of nitrogen-free 

 extract, but the per cent, of fat or oil is small except in such 

 feeds as gluten feed and cotton-seed meal, where the per cent, 

 may be as much as ten or twelve. The per cent, of nitrogen- 

 free extract is usually somewhere around forty in hays, while 

 in seeds it is usually from sixty to seventy-five. A feed which 

 contains a good deal of protein and fat always has a lower per 

 cent, of nitrogen-free extract. 



Besides the above terms roughage and concentrates are 

 often used in speaking of feeds. Roughage refers to all 

 kinds of coarse feed such as hay and fodder. Concentrates 

 is applied to all grains and meals. 



The digestibility of a food has reference to the amount 

 which becomes available for the use of the animal through the 

 action of the various digestive juices in the alimentary tract. 

 It is only the digestible part of the food which the animal can 

 use for making blood, muscle, bone, etc. The undigested 

 part passes off as solid excrement. The digested part which 

 is not stored up in the body is passed off mostly in the liquid 

 excrements along with the wastes of the body. 



The amount of a food which is digestible may be expressed 

 in per cent., and this is called the coefficient of digestibility. For 

 example, the average protein in shelled corn is about 10.3 

 per cent, and its digestibility is about 76 per cent. Then in 

 100 pounds of shelled corn there would be 10.3 pounds of 

 protein, of which 76 per cent., or 7.828 pounds, is digestible. 



