FEED STUFFS AS A SOURCE OF ENERGY 6 1 



body. Should they be fed in excess they are stored as fatty 

 tissue (beef tallow, hog lard, mutton suet, etc.) with which we 

 are all familiar. When protein is fed in larger quantities than 

 needed for the building up and repair of the body tissues it may 

 be used for fuel purposes. The use of protein as fuel is ex- 

 travagant because it costs much more than carbohydrates and 

 fats. The fat of the body is its storehouse of fuel. Animals 

 fed insufficiently draw on their stored up fats and be- 

 come lean. In the production of milk, growth, development 

 of the young, etc., fuel and repair materials are reserved when 

 the nutrients supplied are sufficient. 



Potential and Kinetic Energy. There are two kinds of energy 

 manifested in the animal, namely, potential and kinetic. Poten- 

 tial energy is that which is in the food and stored up in the 

 animal body. It may be likened to a bent spring. Kinetic 

 energy is represented in the animal by work and heat. It is the 

 energy represented in moving bodies and may be likened to the 

 swinging of a pendulum. 



EXAMPLES OF POTENTIAL AND KINETIC ENERGY IN THE ANIMAL' 



Food f 



Feces (manure) 



Fetation | Potential Energy 



Combustible gases I 

 Storage of tissue [ 



{ Kinetic Energy 



Measurement of Energy. There is a great variation in the 

 content of nutrients of the several feeds. In order to deter- 

 mine the amount of energy or heat units in feeds an apparatus 

 is used called the calorimeter. This apparatus is so arranged 

 that the heat given off by burning a feed completely is absorbed 

 by water and the heat units measured or calculated. The prin- 

 cipal units used in measuring heat are the small calorie (c), large 

 Calorie (C) and the therm (t). The large Calorie (written 

 with a capital C) is the amount of heat required to raise the 

 temperature of I kilogram (2.2 Ibs.) of water I degree Centi- 

 grade, or about 4 pounds of water I degree Fahrenheit. The 



1 Armsby, Principles of Animal Nutrition. 



