ENERGY VALUES OF RATIONS FOR FARM ANIMALS. 9 



or less incompletely burned material is also contained in the urine, 

 while ruminants, and to a certain extent horses and swine, also give 

 off combustible gases arising from fermentations in the digestive 

 tract. Thus about 22 per cent of the chemical energy of corn meal 

 and fully 55 per cent of that of average hay has been found to escape 

 in these ways. 



Second, as already pointed out, the animal body has to extract its 

 real fuel material from its feed, separating it from the relatively 

 large proportion of useless material which it excretes. To effect this 

 separation requires work and consumes energy, and this energy, of 

 course, is not available for other purposes. The case is somewhat as 

 if the gasoline engine had to distill its own gasoline and separate it 

 from impurities. Moreover, it appears to be well established that 

 the digestible substances taken up from the alimentary tract act as a 

 direct stimulus to the combustions going on in the body; that is, that 

 the body may burn up more material simply because a larger supply 

 is available, while there is some evidence that an increase in the feed 

 consumed tends to stimulate the minor incidental movements of the 

 animal, or, in other words, to render the animal more restless, espe- 

 cially when standing. 



It is not, then, the total chemical energy contained in a feeding 

 stuff which measures its value as fuel material to the body, but what 

 remains after deducting the losses in the unburned materials of the 

 excreta and the energy expenditure incident to the consumption of 

 the feed. This remainder is called its net energy. 



For example, while 100 pounds of corn meal contain, as stated, 

 about 170.9 therms of chemical energy, only about 88.8 therms re- 

 main, after all these deductions have been made, to represent the 

 actual value of the corn meal as a source of energy to the organism. 



NET ENERGY VALUES OF FEEDING STUFFS. 



While it is a comparatively simple matter to ascertain the total 

 amount of chemical energy contained in a feeding stuff, the determi- 

 nation of the proportion of this energy which the body can actually 

 utilize, i. e., its net energy value, requires the use of complicated and 

 costly apparatus (respiration apparatus or respiration calorimeter) 

 and the expenditure of much time and labor. While much has been 

 accomplished along this line, vastly more still remains to be done 

 before we can claim to have a complete knowledge of the energy 

 values of feeding stuffs. At the same time, enough has already been 

 accomplished, through the investigations of G. Kuhn and of Kellner at 

 the Mockern Experiment Station in Germany, since 1882, and by 

 the experiments carried on, in cooperation with this Department, 

 by the Institute of Animal Nutrition of The Pennsylvania State 

 College, to demonstrate that the method still generally current of 

 60978°— Bull. 459—16 2 



