AVAILABILITY OF ENERGY FOR THE HORSE. 



25 



As is evident from the brief description given of the methods by 

 which the factors are reached, this method of computation is not 

 claimed by its authors to be scientifically exact, but they believe it to 

 be a sufficiently close approximation on which to base computations 

 of rations in practice. 



Zuntz and Hagemann's conclusions have been subjected to con- 

 siderable criticism, the two principal points being, first, their esti- 

 mate of 9 per cent for the work of digestion, based upon the results 

 of experiments on man ; and, second, and more especially, the assump- 

 tion that the metabolism for 24 hours may be computed from the 

 results of comparatively short respiration experiments. Qualita- 

 tively, Zuntz and Hagemann have clearly demonstrated the very 

 considerable expenditure of energy by the horse in the digestion of 

 his feed, as well as the fact that this expenditure is much greater 

 with coarse fodders than with grain, and they were the first to point 

 out that this expenditure of energy must be taken account of in esti- 

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

 opinion as to the quantitative worth of their figures, and certainly 

 investigations by more direct methods, involving fewer assumptions 

 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. 



AVAILABILITY FOB THE HOBSE WOLFF'S BESULTS. 



His extensive investigations upon the working horse, made at 

 Hohenheim in 1877 to 1894 1 and antedating the investigations thus 

 far mentioned, led Wolff to a still simpler approximate method of 

 estimating what in a sense corresponds to the available energy ol 

 the feed of the horse. 



In Wolff's experiments, the horse performed a measured amount of work 

 which was so adjusted in different periods as to be as nearly as possible in 

 equilibrium with the feed consumed. This was considered to be the case when 

 the live weight of the animal remained substantially unchanged for a con- 

 siderable period and when the urinary nitrogen did not show an increase as a 

 consequence of the additional work done. By comparing the work performed 

 on a basal ration with that which could be done with a heavier one, the ratio 

 of the work done to the additional feed consumed was established within the 

 limits of error of the method, this being the prime object of the experiments. 

 This being determined, however, it was a simple matter to compute the amount 

 of feed corresponding to the total work done, while subtracting this from the 

 total ration would give the maintenance ration. The results of these compari- 

 sons, made on the basis of the so-called " digestible nutrients " of the rations 

 (the digestible fat being multiplied by 24) are considered on subsequent pages. 



On the average of a considerable number of comparisons, it was 

 found that the digestible nutrients from coarse fodders were less 



1 Compare pp. 57 to 62. 



