BREEDS OF BEEF CATTLE 297 



Therms. 



Wheat straw 171.4 



Corn meal 170.9 



Oats 180.6 



Wheat bran 175.5 



Linseed meal 196.7 



Utilization of Energy. But the value of a fuel depends also 

 upon how much of the chemical energy which it contains can be used. 

 Hard coal contains plenty of energy, but it would not be of much 

 use to run a gasoline engine. Wheat straw contains fully as much 

 chemical energy as corn meal, but much of that energy can not be 

 utilized by the animal machine. Two causes combine to affect the 

 utilization of the chemical energy contained in feeding stuffs. 



First, more or less of the feed escapes from the body unburned. 

 If a coal is of such quality that portions of it drop through the grate 

 unconsumed, and if smoke and combustible gases are carried off 

 through the stack, it is evident that a ton of it will supply far less 

 heat to the boiler than it would if the combustion were perfect. The 

 case of the feeding stuff is similar. Much of even the best feeding 

 stuffs escapes digestion and is excreted in the dung, carrying with it 

 a corresponding quantity of the chemical energy of the feed. More 

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

 while ruminants, and to a certain extent horses, also give off combust- 

 ible 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 i'; 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, when the animal eats more feed than 

 is required simply to furnish energy to run its machinery, and hence 

 is able to produce meat or milk, the process of converting the food 

 into suitable forms to store up in the body seems to require a 

 further expenditure of energy. 



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 expended in extracting the real fuel ma- 

 terials from the feed and transforming them into substances which 

 the body can use or store up. For example, while 100 pounds of 

 corn meal contain, as stated, about 170.9 therms of chemical energy, 

 only about 88.8 terms remain, after all these deductions have been 

 made, to represent the actual value of the corn meal as a source of 

 energy to the organism. 



Energy Values of Feeding Stuffs. While it is a comparatively 

 simple matter to ascertain the total amount of chemical energy con- 

 tained in a feeding stuff, the determination of the proportion of this 



