CHEMISTRY OF FOODS AND FEEDING. 1181 



some slight variations. If a cow giving milk is supplied with 

 only the exact amount of food required to meet the first three 

 requirements, she will still give some milk, which will be pro- 

 duced from food which should have been used for repairing 

 waste, and the cow will grow thin in consequence. But as far 

 as practical profitable results are concerned the rule as laid down 

 may be considered correct. 



The food required for repair of waste and production of heat 

 and energy is commonly called " food of support ; " it is what 

 keeps the animal alive. Except in the case of the working an- 

 imal, it pays no profit to the feeder; it is the necessary expense 

 of keeping the animal. Under all circumstances a large propor- 

 tion of the food consumed by the animal must be used in this 

 manner, but to secure profit in feeding it is essential that this 

 proportion shall be as small as possible. 



If a farmer feeds three tons of hay, all of which is used by 

 the animals to which it is given as food of support, he will make 

 no profit on it, and get no return for the hay. If he feeds three 

 tons, and two tons are used as food of support and one ton for 

 growth or production of fat or milk, he gets returns for one ton, 

 and the other two tons are the cost of turning one ton into meat 

 or milk. If only one ton is used for food of support, and two 

 tons for growth or production of fat or milk, then he gets two 

 tons converted into profitable forms at the expense of one ton. 



There are two ways in which we may diminish the propor- 

 tion which the food of support bears to the total amount sup- 

 plied. To secure profitable feeding, both these plans must be 

 used. The first is 



Reducing the Food of Support. We have seen that the 

 food of support is used for repairing waste and production of 

 heat and energy. The amount used for the first purpose is small. 

 A half pound of digestible albuminoids, which would be con- 

 tained in two pounds of beans or five pounds of oats, will re- 

 pair the necessary waste of substance during twenty-four hours 

 on an ox weighing one thousand pounds. 



The largest part of the food of support is expended in the 

 production of heat and energy. In order that the animal may 



