pound digestible crude protein or 0.5 pound digestible true protein 

 will suffice for the protein maintenaince of mature cattle. 



The maintenance ration of energy*. 



It has been shown that the maintenance requirement is equiva- 

 lent to the amount of energy consumed during fasting, and that for 

 thin mature cattle this averages about 6.1 Therms per thousand 

 pounds. We have now to inquire how much feed must be supplied 

 to meet this requirement. 



Plainly, the value of a feeding stuff so far as it serves as fuel, 

 depends, in the first place, on how much total energy can be secured 

 from it in the form of heat. This can be measured without difficulty 

 fcy burning the substance, and measuring the heat produced. The 

 following are the results of a few such determinations : 



Total energy in 100 pounds 1 . 



Timothy hay 175.1 Therms 



Clocer hay !73- 2 Therms 



Oat straw 171.0 Therms 



Wheat straw 1714 Therms 



Corn meal 170.9 Therms 



Oats 180.6 Therms 



Wheat bran J 75-5 Therms 



Linseed meal l 9&-7 Therms 



Available energy : But the value of a fuel depends also upon how 

 much of the energy which it contains can be used. Hard coal con- 

 tains plenty of energy, but it would not be of much use to run a 

 gasoline engine. Wheat straw contains fully as much energy as 

 corn meal, but much of that energy cannot be utilized by the ani- 

 mal machine. 



Two causes combine to affect the availability of the energy con- 

 tained 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 



1 With 15 per cent, moisture. 



(12) 



