CHAPTER XXVIII 



FEEDING ANIMALS 



He causeth the grass to grow for the cattle, and herb for the service of 

 man : that he may bring forth food out of the earth. THE BIBLE 



412. Animal products are costly. Farm animals digest less 

 than three fourths of the feed that is given them. About half 

 of the digested portion is required for maintenance, or for run- 

 ning the machinery of the body. Only one fourth to one third 

 of the total nutrients that are fed are therefore available for the 

 production of meat, milk, eggs, wool, or of energy for work. 

 The processes of mastication, digestion, and production use 

 energy also, and there is recovered in the animal product not 

 more than 20 per cent, or one fifth, of the total nutrients fed. 

 An animal is a more efficient machine, however, than any yet 

 devised by man. Man's best machine is the steam engine, which 

 returns at the drive wheel about 10 per cent of the energy 

 contained in the coal which is burned. 



413. The uses of feed. Food for maintenance includes that 

 which is necessary to keep the body temperature uniform. 

 Therefore a part of the food eaten by every animal is used 

 as heating fuel. The animal body is a very complex machine, 

 and, like any other machine, its parts are constantly wearing 

 out. If these parts are not repaired from day to day, the ma- 

 chine gets out of order and fails to work. Some of the feed 

 eaten goes to replace the tissue worn out, or to keep the body 

 in repair. Energy is also constantly required to secure, chew, 



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