ready noted, however, this quantity cannot be determined directly 

 for cattle. The only available method, then is to try various 

 amounts of protein and see how low the supply can be reduced 

 without causing a loss of protein from the body. In considering the 

 results of such experiments, two points must be borne in mind. 



First, if more protein is supplied to the mature animal than it 

 needs for its maintenance, the surplus is practically all broken 

 down and oxidized as fuel to supply energy. The mere fact, there- 

 fore, that there is no loss of body protein on a given ration, while 

 it shows that the protein supply is ample, does not show that a less 

 quantity would not be sufficient. 



Second, when there is an inadequate supply of carbohydrates 

 and fat in the food, protein which would otherwise be used for 

 maintenance may be broken down and used as fuel. The protein 

 supply can be reduced to its lower limit only when there is a liberal 

 supply of fuel material in the ration. 



i 



The question to be considered, then, is what is the least amount 

 of protein which has sufficed to maintain cattle when the total food 

 supply was ample to yield the necessary energy. 



Wolff's standard for maintenance, long current, of 0.7 pounds 

 digestible crude protein per 1000 pounds live weight was based 

 upon experiments by Henneberg & Stohmann in 1858 with the 

 addition of an allowance for the fact that their experiments were 

 made at a relatively high temperature. Wolff's standard, however, 

 was intended as a guide for actual maintenance feeding rather than 

 as an expression of the minimum protein requirement, which, as 

 later experiments show, may be reduced considerably below Wolff's 

 standard. 



Of the more recent experiments, those of Kuhn and Kellner 

 at the Moeckern Experiment Station were the earliest. Of the eight 

 animals experimented upon, seven gained fat during the experiment, 

 showing that the rations contained a sufficient quantity of non- 

 nitrogenous nutrients, while in the remaining cases the loss of fat 

 was relatively small. Dividing the experiments into groups accord- 



(10) 



