50 PRINCIPLES OF FEEDING FARM ANIMALS 



of body protein, and that muscular labor would, therefore, call for 

 heavy protein feeding. This view was held by early investigators, 

 notably by the German scientist Liebig (" The father of agricul- 

 tural chemistry"), but is now long since abandoned. It is true 

 that large amounts of protein may be broken down, as shown by 

 an increased secretion of urea when heavy mechanical labor is per- 

 formed, but this will only take place when the animal is fed a ration 

 insufficient to maintain the body weight, or when the body is in a 

 poor nutritive condition, so that there is but little fat or other 

 non-nitrogenous subsitances in the body to protect the tissues from 

 oxidation. When an animal does a certain work, the oxidation 

 processes going on in the body are increased, and a greater produc- 

 tion of carbondioxide and water follows. There is a direct relation 

 between the amount of work done, the oxygen taken up, and the 

 carbondioxide exhaled. When a. sufficient amount of carbo- 

 hydrates and fat is supplied in the food, they furnish material for 

 the production of the muscular energy, except in cases of very 

 severe labor when the decomposition of nitrogenous tissues may be 

 increased, as shown by the amount of urinary nitrogen excreted. 



The amount of work that can be done on different classes of 



feed components has been found -to stand in a direct relation to 



the amount of net energy that they furnish. As in the production 



,of heat, the different nutrients replace each other for production 



of work in proportion to their contents of net energy. 



Feeding Standards. — The nutrients required by farm animals 

 for productive purposes have been determined as in the case of 

 the maintenance standards. The first attempts to formulate gen- 

 eral standards for farm animals were made by the German scientist 

 Grouven in 1858. He gave the quantities of total dry substance, 

 protein, and fat which an animal of a certain age would require 

 daily in its feed ration. A somewhat later effort in this direction 

 is represented by the standards proposed by Wolff, in which the 

 amounts of digestible components required by different classes of 

 farm animals under varying conditions are given. 



The Wolff feeding standards were brought to the attention of 

 American farmers in the seventies, and, mainly through the publi- 

 cation of Armsby's "Manual of Cattle Feeding," in 1880, they 

 became generally known here as "The German feeding stand- 

 ards." They were modified in 1897 by Lehmann, another German 

 scientist, and ten years later Kellner proposed a new set of stand- 

 ards, based on contents of digestible protein and " starch values " ; 

 i.e., the amounts of different nutrients or feeds equivalent to one 

 pound of starch for the production of body fat by mature fatten- 

 ing steers. These and similar standards suggested by Armsby are 



