298 NUTRITION OF FARM ANIMALS 



horse performed a measured amount of work 1 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 sub- 

 stantially unchanged for a considerable period and when the 

 urinary nitrogen did not show an increase as a consequence 

 of the additional work done (637). 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 com- 

 pute the amount of feed corresponding to the total work per- 

 formed, while the difference between the latter and the total 

 ration evidently was the maintenance ration. From the total 

 digestible nutrients (inclusive of crude fiber) required for main- 

 tenance, as thus computed by Wolff, the equivalent amounts of 

 metabolizable energy required for maintenance may also be 

 computed approximately by the use of Zuntz and Hagemann's 

 factor of 3.96 Cals. per gram (776). 



In Wolff's earlier experiments and in those later ones in 

 which approximately equal proportions of hay and grain were 

 consumed, the maintenance ration was found to be approxi- 

 mately 4200 grams total nutrients per 500 kgs. live weight, 

 equivalent to 16.63 Therms. In those later experiments (in- 

 cluding the results of similar investigations by Grandeau as re- 

 computed by Wolff) in which a larger proportion of grain was 

 fed, the total nutrients required for maintenance ranged from 

 3600 to 3800 grams, equivalent to from 14.26 to 15.05 Therms. 

 In other words, the amount of metabolizable energy required 

 for maintenance varied with the proportion of roughage pres- 

 ent, as would be anticipated from the results with cattle re- 

 corded on previous pages. 



b. Zuntz and Hagemann's results. From a respiration ex- 

 periment at the Gottingen Experiment Station, Zuntz and Hage- 

 mann compute the metabolizable energy of the maintenance 



1 Wolff's experiments were made with a sweep-power arranged to serve also as a 

 dynamometer. The actual measurements of the work performed, except in the later 

 experiments, proved to be too low, but Wolff believes them to be relatively correct, 

 so that the ratio between the work as measured and the additional feed required to 

 produce it may still serve as the basis of computation. 



