H. P. Armsby and J. A. Fries 185 



steer only 1-706 therms out of its total energy content of 1-897 therms. 

 The mean of similar determinations shows that, after deducting the 

 losses in urine and methane, the digestible matter of one hundred pounds 

 of average alfalfa hay, out of its total energy content of 97-9 therms, may 

 supply 80-8 therms of heat to the body. This is its metabolizable energy, 

 or fuel value. But since one pound of starch can supply 1-706 therms, 

 evidently the digestible matter of one hundred pounds of the alfalfa 

 hay yields as much heat as 80-8 -;- 1-706 = 47-37 pounds of starch. In 

 other words, 47-37 pounds of digested starch, instead of 51-6 pounds, 

 would be equivalent as body fuel to one hundred pounds of the hay. 



This figure evidently approximates more nearly to expressing a 

 physiological value than the previous one, but even this reduced value 

 does not measure the actual contribution which the hay can make to 

 the nutrition of the animal, since it fails to take account of the very 

 considerable amount of energy expended in the mechanical and chemical 

 processes incident to the consumption, digestion and assimilation of 

 the feed. It was precisely the special merit of Kellner's researches that 

 they covered this point. He measured the actual amount of energy 

 utilized by the animal and demonstrated that it was notably less, not 

 onl}" than the carbohydrate equivalent of the digested nutrients but 

 also less than the physiological heat value, or fuel value, or metabolizable 

 energy of these nutrients. 



Moreover, not only is the utilizable or "Net" energy of a feeding 

 stuff less than its fuel value, or metabolizable energy, but the two are 

 not even approximately proportional. In Kellner's investigations, as 

 summarized by the senior author^, the percentage of the metabolizable 

 energy which was actually utilized ranged, in round numbers, from 

 18 per cent, in wheat straw to 66 per cent, in cotton seed meal while in 

 our own experiments there was a similar range from 45 per cent, in 

 maize stover to 61 per cent, in hominy feed. In other words, to supply 

 as much metabolizable energy as 100 pounds of hominy feed would 

 require 180 pounds of maize stover, but to supply as much net, or 

 utilizable, energy as 100 pounds of hominy feed would require 243 pounds 

 of maize stover. 



Kellner's starch values were intended to express the net, or utilizable, 

 energy of the feed and not its content of carbohydrates nor its fuel value. 

 Thus the starch value of average alfalfa hay, computed by Kellner's 

 method, is 34-5 pounds per hundred, equivalent to 36-9 therms of net 



• The Nntrition o/ Farm Animals, p. 600. 



