640 



NUTRITION OF FARM ANIMALS 



the digestive tract or in the course of metabolism in the tissues. 

 As stated in Chapter VI (323), this convertible portion of the 

 feed energy has been given various names by different investi- 

 gators, such as " physiological heat value," " fuel value," " avail- 

 able energy," etc., but following a suggestion made earlier by 

 the writer it is here designated as " metabolizable energy." 



747. Method of , determining. As is apparent from the 

 foregoing paragraphs, the direct determination of the metab- 

 olizable energy of a feeding stuff or ration requires the meas- 

 urement of the amounts and heats of combustion of the feed 

 and of the solid, liquid and gaseous excreta by the methods 

 outlined in Chapter VI. These quantities being known, a 

 simple subtraction gives the metabolizable energy. Thus the 

 results of the experiment used as an illustration in Chapter VI 

 (322), put in a somewhat more detailed form, were as follows : 



TABLE 187. EXAMPLE OF DETERMINATION OF METABOLIZABLE ENERGY 



748. Correction for gain or loss of protein. In the foregoing 

 experiment the animal gained 15.2 grams of fat and 66.6 grams of 

 protein and therefore stored up in its body equivalent amounts of 

 energy, viz., 



In protein, 5.7 Cals. X 66.6 = 380 Cals. 

 In fat, 9.5 Cals. X 15.2 = 144 Cals. 

 1 Per gram fresh urine. 



