MAINTENANCE THE ENERGY REQUIREMENTS 301 



The authors conclude, therefore, that when the amount of 

 heat liberated by the digestive work is small the lack is com- 

 pensated for by an increased katabolism of body tissue. Their 

 final result is that their animal required per head at least n.oo 

 Therms of heat to maintain his body temperature. In other 

 words, this is the minimum of metabolizable energy which 

 must be contained in a maintenance ration, since if less be 

 present, even although the ration supply the requisite amount 

 of net energy, body tissue would still be katabolized for the 

 production of the necessary heat. Computed per thousand 

 pounds live weight, Zuntz and Hagemann's estimated main- 

 tenance requirement is : 



Net energy for internal work 4.1 Therms 



Additional required for heat production 7.8 Therms 



Total metabolizable energy required 11.9 Therms 



In computing a ration for the actual maintenance of the 

 horse at rest, it is necessary, according to these figures, to con- 

 sider not only whether it supplies net energy equal to the fast- 

 ing katabolism but also whether it contains sufficient metab- 

 olizable energy to support the necessary heat production. On 

 the other hand no such allowance need ordinarily be made in 

 computing work rations. The horse when at work is producing 

 an excess of heat (compare Chapter XIV) , and during the work- 

 ing hours no expenditure of feed energy for the sake of heat 

 production would be called for, while any ordinary working 

 ration would probably contain a considerable surplus of me- 

 tabolizable energy over the maintenance demand during the 

 hours of rest. 



The maintenance requirement of fowls 



388. Net energy requirements. Gerhartz l has measured 

 the net energy requirement of fowls by means of a num- 

 ber of respiration experiments with the Regnault-Reiset type 

 of apparatus (298) upon two fasting hens. He has also com- 

 puted the fasting katabolism from a number of respiration ex- 

 periments in which the animals were fed by subtracting from 

 the total metabolism that computed to have been due to the 



1 Landw. Jahrb., 46 (1914), 797. 



