Mar 2s, 191S Energy Values of Feeding Stuffs for Cattle 439 



I. LOSSES OF CHEMICAL ENERGY— METABOLIZABLE ENERGY 



The losses of chemical energy occur substantially in the feces and 

 urine and in the combustible gases. 



The energy content of the dried feces and urine is readily determined. 

 In investigations at this Institute, Braman (16) has shown that the loss 

 of energy in the drying of urine may be estimated with a good degree 

 of accuracy, the error being insignificant in comparison with the total 

 energy of the feed. The possible loss of energy in the drying of the 

 feces has not yet been investigated directly, although Fingerling, Kohler, 

 and Reinhardt (18) have obser\'ed a loss of carbon, the amount of which 

 they do not state. 



The energy content of the combustible gases is not susceptible of 

 direct determination, but must be estimated from their chemical com- 

 position. The combustible gases which have been actually identified as 

 excreted by cattle are methane and hydrogen. All investigations are in 

 accord in showing that the former is the chief product of the normal 

 fermentations occurring in the digestive tract, but results differ regarding 

 the extent to which hydrogen is formed. In our experiments the gases 

 were analyzed by passing them over platinized kaolin at a red heat. 

 By this method in almost every instance a ratio of C to H slightly greater 

 than that in CH^ (2-976 to i) has been found, the average of 57 experi- 

 ments reported by the junior author elsewhere (19) being 3.167 to i, 

 with considerable variations in individual cases. We are inclined to 

 think that this high figure is due to failure to oxidize the last traces of 

 hydrogen in the combustion tube. On the other hand, Markoff (37, 38), 

 in his extensive investigations of paunch fermentation in cattle, found 

 in nearly every instance a small amount of hydrogen, and Von der Heide, 

 Klein, and Zuntz (20), in respiration experiments upon an ox, observed 

 a small excretion of hydrogen in two cases out of four. In computing 

 the energy losses in the following experiments it has been assumed that 

 the combustible gases consisted of CH^ (methane), and the computa- 

 tions have been based upon the observed quantity of carbon. 



The difference between the chemical energy of the feed and that lost 

 in the excreta shows how much of the former is capable of being con- 

 verted into other forms in the body, either during the changes which the 

 feed undergoes in the digestive tract or in the course of metabolism in 

 the tissues. This convertible portion of the feed energy has been given 

 various names by different investigators, such as "physiological heat 

 value," "fuel value," "available energy," etc. Without entering here 

 into a discussion of the propriety of these names, we have preferred for 

 our present purpose to follow the suggestion made earlier by the senior 

 author (2, p. 270) and to designate it as " metabolizable energy." By 

 this term is meant simply the energy capable of transformation in the 

 body, with no implications as to the proportion of the energy thus trans- 



