CHAPTER XX 



MAINTENANCE EATIONS 



A MAINTENANCE ratiou is one supplying the needs 

 of an animal withont production of any kind and with 

 no loss of body substance. To be more specific, when 

 an ox doing no work excretes just the quantities of 

 nitrogen and carbon that are contained in the food con- 

 sumed, he is said to be eating a maintenance ration. 

 The work done by the animal at rest is largely needed 

 in the following directions: the chewing of food and 

 its movement along the intestinal tract; the muscular 

 action of the heart in causing blood circulation, and the 

 metabolic activity of the cells in causing the chemical 

 transformation of the nutrients. Some work is also 

 done in moving the body. The demands upon the food 

 for maintenance purposes are therefore entirely for the 

 production of muscular energy and heat. 



Nine -tenths or more of a maintenance ration may 

 consist of carbohydrates which, because the income and 

 outgo are balanced, are used solely as fuel. Only a very 

 small amount of protein is necessarily destroyed by a 

 resting animal, although a minimum food supply is 

 absolutely essential if the nitrogenous tissues of the 

 body are to be kept from wasting. If an animal is 

 not eating protein, urea will continue to appear in 



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