Mar. 25. 191S Energy Values of Feeding Stuffs for Cattle 483 



III. NET ENERGY VALUES AND THEIR COMPUTATION 



The method of estimating the nutritive values of the feeding stuffs 

 consumed by farm animals which has been current for many years may 

 from one point of \aew be characterized in a broad way as a chemical 

 method. On the basis of the fundamental investigations of Henneberg 

 and Stohmann (21, 22) in the early sixties, it sought to deteiTnine the 

 amounts of protein, carbohydrates, and fat contained in feeding 

 stuffs in a digestible form, assuming that the groups thus determined 

 had the same physiological values in the nutrition of herbivora as had the 

 corresponding substances in the food of man and carnivora. It is a 

 well-recognized fact, however, that our information regarding both the 

 qualitative and quantitative composition of feeding stuffs is even yet 

 very meager. Moreover, our knowledge of the physiological functions 

 of their ingredients is even more defective, so that, as Kellner (24, p. 15) 

 points out, the advances in our knowledge of the chemistry of plants have 

 not led to a corresponding increase in our knowledge of their nutritive 

 values and have left the methods for the analysis of feeding stuffs largely 

 untouched. 



Kellner appears to have been the first to attempt any practical appli- 

 cation of the conception of the feed as a source of energy to the body. 

 In 1880, in his investigations upon the relations between muscular acti\dty 

 and metabolism in the horse (23), he determined the additional amount 

 of work which the animal was able to perform as a result of the addition 

 to his rations of starch and of fat. He expressed his results in terms of 

 the percentage of the energy of the starch or fat which was recovered as 

 useful work and called attention to the desirability of determinations of 

 the heats of combustion of nutrients and feeding stuffs. Sixteen years 

 later, after Rubner (40, 41) had published his fundamental work on the 

 replacement values of nutrients and Zuntz and his associates (30, 54) had 

 begun their investigations on the metabolism of the horse from the stand- 

 point of energy, Kellner was able to return to the subject and undertake 

 those extensive investigations with cattle (cited on previous pages) upon 

 which he based his well-known method of comparing feeding stuffs on the 

 basis of their so-called starch values. These are in reality energy values, 

 and, so far as they are the results of direct determinations, they were 

 obtained by substantially the same general experimental methods used 

 in our own investigations, although direct determinations of the heat 

 production were not included. 



VALUKS DIRECTLY DETERMINED 



The net energy value of a feeding stuff, as slated in the introductory 

 paragraphs, is the energy which remains after deducting from its total 

 chemical energy the two classes of losses which have been discussed in 

 the first two sections of this article — viz, the losses of chemical energy 



