232 NUTRITION OF FARM ANIMALS 



and gaseous, as measured by their heats of combustion. If, 

 then, the gross energy of the total excreta be subtracted from 

 the gross energy of the feed, the remainder shows how much 

 of the chemical energy of the feed can be metabolized, that is, 

 converted into other forms in the organism. To this difference, 

 the term metabolizable energy has been applied. 



Metabolizable energy may be briefly defined as the gross 

 energy of the feed minus the gross energy of the excreta. Thus 

 in the experiment cited previously (294) to illustrate the 

 method of determining the balance of matter, the energy content 

 of the feed and excreta and the metabolizable energy of the 

 total ration were as follows : 



Energy of feed 



6988 grms. timothy hay 27,727 Cals. 



400 grms. linseed meal 1811 Cals. 



29,538 Cals. 

 Energy of excreta 



16,619 grms. feces 14,243 Cals. 



4357 grms. urine 1210 Cals. 



142 grms. methane .... 1896 Cals. 



Total ! ! ! . 17,349 Cals. 



Metabolizable energy 12,189 Cals. 



It should be observed that the foregoing definition makes no 

 assertion whatever as to the forms into which the metabolizable 

 energy has been transformed nor as to the degree to which the 

 transformation has been of service to the organism. Some of 

 the energy, for example, may be retained in the body in a gain 

 of fat or protein, as in the illustration just given, i.e., it may 

 be temporarily set aside as a reserve to be used later, but it is 

 still capable of transformation into other forms and therefore 

 constitutes a part of the metabolizable energy. On the other 

 hand, the feed might contain some substance capable of oxida- 

 tion in the body but of no physiological value to it and which 

 was simply burned to get rid of it. The heat thus generated 

 might be entirely useless to the animal, yet this energy 

 would be part of the metabolizable energy of the feed. Some- 

 what similarly, the energy liberated as heat in the methane 

 fermentation constitutes part of the metabolizable energy, 

 although it does not enter into the tissue metabolism. Metab- 



