276 DAIRY CATTLE AND MILK PRODUCTION 



Fat or Ether Extract. That part of the foodstuff that 

 will dissolve out in ether is called ether extract. It consists 

 mostly of fats, but sufficient other products to make it some- 

 what inaccurate to call this group fat, although this term is 

 often used. 



The crude fiber, nitrogen free extract, and fat all serve 

 much the same purpose in the body. They supply heat to 

 keep the body warm, material to be built into fat and to be 

 burned or oxidized in the body to furnish energy. All feed 

 stuffs contain these same constituents, but in widely varying 

 quantities. 



Digestibility. However, the animal is not able to digest 

 all of the substances in any foodstuff. The proportion of the 

 protein, for example, that may be used depends largely upon 

 the nature of the feed under consideration, the grains being 

 more thoroughly digested than the hays. The amount of 

 each of the substances given that can be digested from any 

 feed stuff by the animal is determined by what are termed 

 digestion trials. The chemist makes such a trial by analyz- 

 ing the food consumed during a certain period by an animal, 

 and at the same time collecting all the dung excreted and 

 analyzing that to find out how much passes through the ali- 

 mentary canal. The difference between the amount con- 

 sumed and the amount voided is called digestible. Such 

 tests have been made of all common feeding stuffs, so the 

 practical feeder has data at hand regarding both the com- 

 position of feeds and their digestibility to serve as a guide in 

 preparing suitable ration. 



The Feeding Standard. The many analyses which have 

 been made enable us to know how much of each of the several 

 constituents is contained in all common feeds on the average. 



