WORK PRODUCTION 563 



The extensive investigations on the work horse initiated at Hohen- 

 heim by Kellner and continued under Wolff's direction, and which 

 have been referred to in Chapter VIII (386 a) in their bearing upon 

 the maintenance requirement, were intended primarily to determine 

 the energy requirements for work. Unfortunately, however, as there 

 noted, the measurements of the work done in the earlier experiments 

 were subsequently discovered to be inaccurate. In the comparatively 

 few later experiments of 1891-94, various mixed rations were fed. 

 While, therefore, the total energy consumed per unit of work could 

 be computed, only few and uncertain data for individual feeding 

 stuffs can be deduced and the results are therefore of small general 

 value for the particular phase of the subject under discussion here. 



671. Net energy values for work production. The ques- 

 tion of the energy requirement of the work animal may, how- 

 ever, be approached in a somewhat different way. 



The energy expended in work production, as already stated 

 (630, 631) , is derived primarily from the katabolism of body sub- 

 stances. The function of the feed so far as energy is concerned 

 is to replace in the body the energy thus expended. The net 

 energy value of a feeding stuff for work production, then, is 

 measured by the amount of body energy which it can thus re- 

 place. The case is precisely parallel to that of maintenance as 

 discussed in Chapter VIII (370). The net energy value of a 

 feeding stuff for the latter purpose is measured by the extent to 

 which it prevents loss of body energy as a consequence of in- 

 ternal work, while the net energy value for the former purpose 

 is measured by the extent to which it prevents or makes good 

 a loss of body energy due to external work. Conversely, the 

 working animal requires in addition to maintenance a supply 

 of net energy in its ration equal to the amount of body energy 

 katabolized for work production. 



In view of this close similarity between the functions of feed 

 in maintenance and in work production, the assumption seems 

 warranted that the net energy values of feeding stuffs for these 

 two purposes are substantially the same. Thus in an exper- 

 iment with a steer already described (364), it was found that one 

 pound of timothy hay contributed 502 Cals. to the maintenance 

 of the animal. If the same animal had been required to do 167 

 Cals. of external work and had performed it with the same aver- 

 age net efficiency as the horse, viz. , about one- third, he would have 



