234 



NUTRITION OF FARM ANIMALS 



1885 and to his isodynamic values based upon them. In the 

 light of the knowledge available at that time, this use of the 

 term was perhaps justified, but as will appear later (369), it has 

 since been shown that part of the metabolizable energy of the 

 feed is virtually available for heat production alone, while only 

 the remainder can be used for general body purposes. If the 

 use of the term available energy is to be continued, therefore, 

 it becomes necessary to distinguish two degrees of avail- 

 ability, using, for instance, the term gross available energy as 

 equivalent to metabolizable energy and net available energy 

 to signify that part of the metabolizable energy which is avail- 

 able for other purposes than heat production. 



In the writer's judgment, simplicity and clearness of concep- 

 tion will be promoted by discontinuing altogether the use of the 

 term available energy and employing the term metabolizable 

 energy, or perhaps fuel value provided the latter is understood 

 with the proper restrictions, to designate that portion of the 

 gross energy of the feed which is capable of transformation in 

 the animal organism. 



324. Factors for metabolizable energy. Rubner, and 

 subsequently Atwater, have proposed factors by the use of 

 which the metabolizable energy of the diet of man may be 

 computed with a considerable degree of accuracy. 1 



TABLE 27. FACTORS FOR METABOLIZABLE ENERGY OF HUMAN FOOD 



The use of these same factors yields approximately correct 

 results for carnivora. They have sometimes been applied also 

 to the digestible nutrients of the feed of herbivora but without 

 sufficient warrant. 



Compare the writer's Principles of Animal Nutrition, pp. 272-281. 



