568 NUTRITION OF FARM ANIMALS 



gross efficiency of the body, however, this percentage will vary 

 from case to case. It will increase with the intensity of the 

 work and decrease with the number of hours the animal is idle 

 per day, i.e., it will vary as the ratio of useful work to main- 

 tenance requirement varies. In the case supposed, the animal 

 worked 6 hours per day. If we imagine his bodily machinery 

 stopped for the remaining 18 hours, as an engine might be, and 

 charge him with only J of his 24-hour maintenance require- 

 ment, the total feed energy necessary would be reduced to about 

 45.230 Therms and the over-all efficiency during the hours of 

 work, computed on this basis, would be 6.26 per cent, or about 

 that of a modern steam locomotive. In actual practice, the con- 

 ditions with an animal are very much as if it were necessary to 

 keep up a full head of steam for 24 hours or as if an internal com- 

 bustion motor were to be run continuously although actual 

 work was being done for only a portion of the time. 



