98 PRINCIPLES OF FEEDING FARM ANIMALS 



special cases, it supplies energy in the form of heat to keep 

 the body warm; and (3) if the supply is in excess of the 

 demands of the body for the first and second purposes, a 

 portion of it may be stored up as gain of body tissue, espe- 

 cially as fat, or it may be used for milk production. 



The work of the animal body may be regarded as made 

 up of the following forms: (1) work of the vital processes, 

 including circulation and respiration ; (2) work of digestion 

 and absorption, including mastication, swallowing, rumina- 

 tion, peristaltic movements, and the activity of the various 

 digestive glands ; and (3) work of the voluntary muscles, 

 such as walking and puUing. 



The following diagram modified from Armsby,^ briefly 



summarizes the uses of the metabolizable energy of the 



feed: 



Of vital process 

 ' Work { Of digestion and absorption 

 Of voluntary muscles 



Metabolizable 

 energy 



Heat production 

 I Storage of energy 



Work of the Vital Processes. — A certain amount of energy 

 is in constant demand for the performance of the work of 

 the vital organs, such as the heart and lungs. The amount 

 of energy expended in this manner is not under control of 

 the animal, as these organs cease their labors only at death. 

 Thus, it is apparent that in the hving animal there always 

 is an expenditure of a certain amount of energy for carrying 

 on the vital processes of the body. If there is not enough 

 energy in the ration for this purpose the animal uses its body 



1 " Principles of Animal Nutrition," p. 339. 



