36 



MAINTENANCE RATIONS OF FARM ANIMALS. 



puted fasting katabolisui and a the tangent of the angle between AB and the 

 horizontal axis (equaling in this case 0.565), or the percentage availability, 

 while OC (equal to 9.S94 therms) is the maintenance ration in terms of the 

 metabolizable energy of this particular hay. 



The fasting katabolism being a constant quantity under like con- 

 ditions, it follows that an amount of any feed capable of supplying 

 5.590 therms of available energy would have been a maintenance 

 ration for this animal. It is clear then that the actual weight of 

 feed required for maintenance will vary inversely as the availabil- 

 ity of its energy. With this particular hay, it would have been nec- 

 essaiw to use an amount containing 9.894 therms of metabolizable 

 energy. With the timothy hay used in an earlier experiment, how- 

 ever, 62.9 per cent of whose metabolizable energy was found to be 

 available, corresponding to the line DG in figure 1, it would have 

 been necessary to use a quantity containing only 5.590-f-0.629= 

 8.888 therms, represented in the figure by OG, in order to supply 

 the requisite available energy and secure maintenance. On the other 

 hand, with a coarser forage having, e. g., an availability of only 

 45 per cent, represented b}^ DH, it would have been necessary to 

 supply 5.590-1-0.45== 12.420 therms of metabolizable energy, repre- 

 sented in the figure b}^ the line OH. Just as was illustrated pre- 

 viously in the case of the dog, while the real requirement of energ}' 

 for the vital processes remains unchanged the amount of feed nec- 

 essary for maintenance is variable, depending upon the availability 

 of its energy. 



If with Zuntz we regard the increased katabolism consequent 

 upon taking feed as representing energy expended in its digestion 

 and assimilation, we may state the case in a slightly different way. 

 We may compare the work thus done to the work of placing the fuel 

 under a factory boiler. If this is done by means of power derived 

 from the same boiler, it is evident that the farther the fuel has to 

 be moved and the greater the amount of incombustible waste which 

 it contains, the larger will be the fraction of the total boiler power 

 required simply to keep the fire going and the less the proportion 

 available for running the factory. So in the body, the greater the 

 amount of energy which must be expended on the food in order to 

 prepare it for its functions in the body the less is the proportion of 

 its energy which is available for carrying on the physiological 

 processes. 



RELATION OF MAINTENANCE REQUIREMENT TO LIVE WEIGHT. 



Before taking up the specific maintenance requirements of farm 

 animals, it is necessary to consider the influence of size and weight 

 upon the maintenance requirement. 



