PROTEIN REQUIREMENT OF CATTLE. 



89 



ment be considered to be 500 grams of true protein or 550 grams of 

 crude protein. Only when the proportion of nonprotein to true pro- 

 tein varies widely from that existing in the rations used in determin- 

 ing the protein requirement will any significant error arise in comput- 

 ing rations. 



In the results considered on succeeding pages, both the crude pro- 

 tein and true protein of the rations are stated when these are given 

 in the reports of the experiments. 



MINIMUM OF PROTEIN FOR FARM ANIMALS. 



In considering the protein supply of different species of farm 

 animals, it is important to distinguish between two points of view. 

 On the one hand, it may be sought to determine the least amount 

 of protein upon which the protein tissues of the animal can be 

 maintained. This might be called the physiological minimum. It 

 shows the proportion of protein in a productive ration which is de- 

 voted solely to maintenance. On the other hand, the endeavor may 

 be to formulate the most advantageous amount of protein to supply 

 when an animal is actually to be maintained for a time and this 

 amount may very possibly be greater than the physiological mini- 

 mum. The first point of view, however, is plainly the fundamental 

 one and should receive our first consideration. Having determined 

 the lower limit of protein supply, it will then be possible to consider 

 intelligently the advantages, if any, of a surplus. 



CATTLE. 



For obvious reasons it is impracticable to ascertain the fasting 

 katabolism of ruminants ; their maintenance requirement as regards 

 protein must, therefore, be determined by a process of trial. 



Tlie earliest, and for a long time the only, determinations of the maintenance 

 requirements of cattle were those of Henneberg and Stohmann in 1S5S, the 

 results of which as regards energy were cited on page 39. In 6 experiments 

 the minimum amount of digestible crude protein (total nitrogen X 6.25) sup- 

 plied per day was 0.35 pound per 1,000 pounds live weight and this quan- 

 tity seemed to be more than sufficient for maintenance. On the average of the 

 6 experiments, in 2 of which there was some loss of body protein, 0.53 

 pound of digestible crude protein was consumed per 1,000 pounds live 

 weight. Wolff's standard for maintenance, long current, viz, 0.7 pound di- 

 gestible crude protein, was based on Henneberg and Stohmann's experiments 

 with 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. 



In the light of later experience, the methods of these earlier experiments 

 must be considered imperfect and their results are now chiefly of historical 

 interest. The first experiments by modern methods were those of G. Kiihn and 



