MAINTENANCE THE ENERGY REQUIREMENTS 309 



work, will give rise to the production of an amount of heat 

 just sufficient to balance the unavoidable loss of heat to the 

 surroundings. 



This influence of the quantity of feed is well illustrated by 

 the following tabulation of Rubner's results upon a dog at 

 different temperatures and consuming different amounts of 

 meat. 



TABLE 56. INFLUENCE OF EXTERNAL TEMPERATURE ON HEAT 

 PRODUCTION 



The amount of feed required to just offset the cooling effect 

 of a low temperature might be called the critical amount of 

 feed for that temperature. It will obviously be less the greater 

 the proportion of its metabolizable energy which is dissipated 

 as heat. 



For example, in discussing the relative amounts of different 

 feeds necessary for maintenance (375) it was stated that either 

 13.83 Ib. of mixed hay or 9.07 Ib. of mixed grain and alfalfa 

 hay would yield approximately 6.0 Therms of net energy, and 

 would therefore constitute a maintenance ration for a 1000- 

 pound steer. The amounts of metabolizable energy contained 

 in these two rations, however, would be different, viz. : 



13.83 Jb. mixed hay 



~ "" Ib. mixed grain and alfalfa hay 



9.07 



12.01 Therms 

 10.69 Therms 



Since both are maintenance rations, the animal would neither 

 gain nor lose energy and all the metabolizable energy of the 

 feed would be finally converted into heat in both cases. The 



