MAINTENANCE AND PRODUCTIVE VALUES 289 



MAINTENANCE AND PRODUCTIVE VALUES 



The animal uses the energy of its food for three pur- 

 poses: For maintenance of life, for external work, and 

 for fattening or the production of eggs, milk, or other 

 product. 



266. Maintenance. Even while at rest, many parts 

 of the body are active. To maintain this activity, requires 

 a supply of energy in the feed. If feed is withheld, the 

 animal will use the substance of its own body to keep 

 up the life functions. When the supply in the body is 

 no longer available, the animal will die. 



267. External Work. When the demands for main- 

 tenance are met, the animal may use the extra energy 

 for carrying loads. The energy stored in the -body may 

 also be used for this purpose, but if this is done the animal 

 gets poor in flesh. 



268. Production. An excess of food above the main- 

 tenance requirement may also be used to store up meat 

 or fat in the body, or for the formation of wool, milk or 

 eggs. 



269. Energy Lost in Digestion and in Production. 

 Formerly, it was considered that the maintenance values 

 of the feeds were in proportion to the total digestible 

 nutrients. We still compare foods on this basis in com- 

 puting balanced rations, because we do not have any 

 better means of comparison at the present time. 



Armsby 1 has studied a few feeds in order to determine 

 how much of the energy is available for maintenance 

 and for production. For these investigations he constructed 



i Pennsylvania Bulletin No. 84 



