THE PRODUCTION VALUES OF FEEDING STUFFS 677 



As is evident from the methods by which the factors were 

 reached, this method of calculation is not strictly exact, but the 

 authors believe it to be a sufficiently close approximation on 

 which to base computations of rations in practice. 



Zuntz and Hagemann's method of computation has been the subject 

 of considerable criticism, the two principal points being, first their 

 estimate, based upon the results of experiments on man, of 9 per cent 

 for the effect of the digestible nutrients, and second, and more es- 

 pecially, the assumption that the metabolism for 24 hours may be com- 

 puted from the results of comparatively short respiration experiments. 

 Qualitatively, Zuntz and Hagemann have clearly demonstrated 

 the very considerable increase of energy metabolism in the horse 

 during the digestion of his feed, as well as the fact that this increase 

 is relatively greater with roughage than with grain, and they were 

 the first to point out that this effect must be taken into account in 

 estimating the values of feeding stuffs. There may be a difference 

 of opinion as to the quantitative accuracy of their figures and cer- 

 tainly investigations by more direct methods, involving fewer assump- 

 tions and complex calculations, are greatly to be desired, but until 

 such results are obtained, we may continue to use provisionally those 

 reached in the manner just described. 



i 779. Wolff's method of computation. His extensive investiga- 

 tions upon the working horse made at Hohenheim in 1877 to 1894 

 and antedating the investigations thus far mentioned, led Wolff to 

 a still simpler approximate method of estimating the relative net 

 energy values of feeds for the horse. 



It was shown, on the average of a considerable number of compari- 

 sons, that the digestible nutrients from roughage were less efficient 

 both for work production and for maintenance than were those derived 

 from grain. Wolff found, however, that if the digestible crude fiber 

 were omitted from the comparisons, the ratio between the fiber-free 

 nutrients and the work performed was comparatively uniform and 

 also that this assumption yielded uniform results for the amount of 

 fiber-free nutrients necessary for maintenance. He therefore con- 

 cluded that, the crude fiber in the rations of the horse was apparently 

 valueless and that the remaining digestible nutrients might be re- 

 garded as of equal value whether derived from grain or from roughage. 

 Expressed in the light of our present conceptions, this is practically 

 equivalent to saying that the net energy value is proportional to the 

 amount of fiber-free nutrients. 



Wolff is careful to say that the digestible crude fiber is apparently 

 valueless, and virtually regards the amount of crude fiber as furnish- 

 ing a convenient empirical measure of the difference in the value of 



