294 THE FEEDING OF ANIMALS , 



391. Physiological requirements. — ^The physiological 

 requirements of the animal must be considered. A 

 ration of maximiun physiological efficiency and economy 

 must contain the several nutrients in such quantities and 

 proportions as will meet the needs of the particular 

 animal fed, without waste. This statement is based upon 

 facts given elsewhere in this volume relative to the 

 demands of the animal body and the functions of the 

 nutrients. 



It remains now for us to consider how to compound 

 such rations as are desired, or those that are adapted 

 in kind and quantity to the requirements which they 

 are to meet. Obviously, the first essential for doing 

 this is the adoption of standards to which rations should 

 conform, for if we do not have these there is no possi- 

 bility of concluding whether one food mixture is better 

 or worse than another for a particular purpose. 



392. Feeding standards. — Such standards have been 

 proposed, which we knew first as German feeding stand- 

 ards. The standards that are now accepted are the 

 result of numerous and elaborate studies of the balance 

 of loss or gain to the animal organism when rations of 

 various kinds were fed to animals at rest, at work, and 

 when producing meat, wool, or mQk, in desirable quan- 

 tities. They relate entirely to physiolpgical demands 

 without reference to the cost of the rations or to the 

 profits which may result from their use. 



The eatlier standards were developed duefly in Ger- 

 many but those now most in favor are based upon Ameri- 

 can experimental data. 



These standards are variable in two main factors: 

 (1) The quantity of available nutrienjts, and (2) the 

 relative proportions of the classes of nutrients. Quan- 



