96 DAIRY FARMING 



includes sufficient other products to make it somewhat 

 inaccurate to call it fat. 



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

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

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

 be burned or oxidized in the body to furnish energy. 



89. Digestibility. An 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. The grains are more thoroughly 

 digested than the hays. The amounts of each of the sub- 

 stances that can be digested from any feed are determined 

 by what are called digestion trials. The chemist makes 

 such a trial by analyzing the food consumed during a certain 

 period, and at the same time collecting all the dung excreted 

 and analyzing that to find out how much passes through 

 the alimentary canal. The difference between the amount 

 consumed 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 rations. 



90. Production Values. The values of different feeds are 

 not always in proportion to the digestible nutrients. If a 

 food is hard to digest, some of the energy derived from it is 

 required to make up the loss due to the hard work of diges- 

 tion. Corn and other grains are easily digested, and for this 

 reason, energy from grains is worth more to the animal than 

 is the same amount of energy from timothy hay or other 

 coarse feeds. Timothy hay if burned gives off as much heat 

 or energy as does corn meal, but, in one experiment, Armsby 

 found the animal digested only 44 per cent of the timothy, while 



