100 PRINCIPLES OF FEEDING FARM ANIMALS 



stimulation of the metabolism by the products of digestion, 

 the fact remains that there is a considerable amount of energy 

 wasted in the form of heat when an animal consumes a feed. 

 Armsby found that in case of steers about one-fourth of the 

 gross energy of the ration was liberated in the form of heat. 

 This means that a certain amount of the metabohzable 

 energy of the ration is wasted as far as having any value 

 for maintenance of, or production by, the animal is con- 

 cerned. 



Net Energy. — The part of the metabohzable energy of 

 a feed which remains after deducting the amount of energy 

 expended in the so-called '' work of digestion," is called its 

 net energy. The net energy is the measure of the net 

 advantage derived by the body from the feed. In other 

 words, the net energy of a feedingstuff represents the amount 

 of energy which it may contribute to the animal body for 

 maintenance and for productive purposes. Mathematically, 

 the net energy may be defined as the gross energy minus the 

 losses of chemical energy in the excreta and the increased 

 heat production consequent upon the consumption of the 

 feed. 



Returning again to the comparison of the animal body 

 with the steam engine, we may assume that the engine is 

 self-stoking. In that case, not all of the energy hberated 

 under the boiler is available to the engine for the production 

 of work. A certain amount of it must be expended for the 

 operation of the self-stoking apparatus which puts the fuel 

 under the boilers. This expenditure of energy corresponds 

 to the expenditure in the animal Ixxly for the digestion, 

 absorption, and distribution of the nutrients of the ration. 

 The amount of the energy of the coal which remains after 



