26 



MAINTENANCE RATIONS OF FARM ANIMALS. 



efficient both for work production and for maintenance than were 

 those derived from grain, and Wolff also cites the results of Gran- 

 deau and Le Clerc's experiments in Paris which show the same 

 general result. Wolff shows, however, that if the digestible crude 

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

 nutrients and the work performed is comparatively uniform and 

 also that this assumption yields uniform results for the fiber- free 

 nutrients required for maintenance. He therefore concludes that the 

 crude fiber in the rations of the horse is apparently valueless and that 

 the remaining digestible nutrients may be regarded as of equal value 

 whether derived from grain or from coarse fodders. Expressed in 

 the light of our present conceptions, this is practically equivalent to 

 saying that the expenditure of energy in digestion is proportional to 

 the metabolizable energy of the crude fiber, or that the available 

 energy 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 nutritive 

 value of the digestible nutrients of coarse fodder as compared with 

 those of grain. That such is the case is doubtless explained in part 

 by the rather limited variety of feeding stuffs employed in the experi- 

 ments. The coarse fodder was meadow hay, with, in some cases, a 

 small addition of straw, while the grain was usually oats, partially 

 replaced in some cases by other feeds. Whether the same relation 

 between fiber-free nutrients and work done would hold in widely 

 different rations is not apparent. 



It should be borne in mind that in reality Wolff's results are rela- 

 tive only. They do not show the actual amount of available energy 

 in the feed or ration, but only that it is proportional to the fiber-free 

 nutrients. The energy of the latter would differ considerably from 

 the available energy as computed by Zuntz and Hagemann's method, 

 first, because it does not include the deduction of 9 per cent for di- 

 gestive work ; and, second, because it assumes a uniform value of zero 

 for crude fiber, while Zuntz and Hagemann's method gives the crude 

 fiber a negative value if it has a digestibility of less than 55 per cent. 

 The values computed according to Wolff's method from the fiber-free 

 nutrients are therefore considerably higher than Zuntz and Hage- 

 mann's figures. 



AVAILABILITY FOR CARNIVORA. 



For many years it was taught, in accordance with Rubner's theory 

 of " isodynamic replacement" (compare p. 72), that with carnivora 

 the nutrients were of value in proportion to their content of metab- 

 olizable energy. Rubner's own later investigations, 1 however, have 



1 Die Gesetze des Energieverbrauchs bei der Ernahrung. 



