ENERGY IN FEEDINGSTUFFS AND ITS USES 95 



the bomb. Figure 21 shows a cross-section of a bomb calo- 

 rimeter. 



The gross energy of one pound of each nutrient is approxi- 

 mately as follows: protein, 2.6 therms; carbohydrates, 1.9 

 therms ; and fat, 4.2 therms. The gross energy of the hays 

 and straws is about 1.7 therms per pound, while that of the 

 grains and other concentrates usually is from 1.7 to 2.0 

 therms per pound. A knowledge of the gross energy values 

 of feedingstuffs, however, is of Httle practical value, as it 

 rarely if ever happens that all of the energy stored up in the 

 feed is available to the animal for its life processes. 



Metabolizable or Available Energy. — Not all the energy 

 of a feedingstuff is accessible to the animal body. Some of 

 the energy of the feed passes through the body in unhberated 

 form in the feces as the undigested food residue. Some of 

 the energy passes out of the body unliberated in the form of 

 combustible gases, as methane and hydrogen, which are 

 formed during the fermentation of the feed in the rumen and 

 large intestine. Further, some unhberated energy is lost by 

 the excretion of only partially oxidized substances, as urea 

 in the urine. 



Thus one must differentiate between the amount of the 

 gross energy of a feed and the amount of energy which 

 actually is liberated or made available in the animal body. 

 That part of the gross energy which may be Uberated in or 

 utihzed by the animal in the processes of metabolism is 

 called the metabolizable energy or available energy of the 

 feed. Mathematically, the metaboHzable energy of a feed- 

 ingstuff may be regarded as the total energy of the feed less 

 the energy of the feces, urine, and excreted gases. 



The gross energy of a feed may be compared to the heat 



