THE MINIMUM PROTEIN REQUIREMENTS 

 OF CATTLE 



H. H. Mitchell 



PRELIMINARY CONSIDERATIONS 



The question of protein requirements of farm animals possesses both a 

 scientific and a practical significance. It is obvious that the food require- 

 ments of animals and the factors modifying these requirements are 

 legitimate subjects for scientific research whether they relate to farm 

 animals of great economic importance to man, or to laboratory animals 

 of no economic importance, or to man himself. In each case the problems 

 involved are those of experimental biology, and the results obtained will 

 aid in a better understanding of the science of nutritional physiology. 

 "\K Experimental investigations with farm animals which deal with the 

 ■s^ entirely practical questions of feeding and management are more under- 

 ^ standable, more readily explainable, and hence more intelligently appli- 

 ■v^: cable the more exact and extensive is the available knowledge of the food 

 <, requirements of such animals. For example, the favorable effect of the 

 addition of a nitrogenous concentrate to the ration of fattening cattle 

 may be due to its content of protein or of phosphorus, or it may be due 

 to some unknown specific effect of the concentrate on the digestive tract 

 resulting in a greater desire for food and a greater consumption of it. 

 Obviously, the decision as to which of these possible explanations is cor- 

 ^- rect will have much to do with the practical application of the experi- 

 ^ mental finding to other rations than those used, and even to other 

 '>- nitrogenous concentrates. The greatest return from even these wholly 

 ■^ practical investigations can be realized only when their results are as 

 completely explainable as the control and the measurement of experi- 

 mental conditions will permit. Complete and accurate information 

 regarding the nutrient requirements of farm animals and the nutritive 

 f value of farm feeds will obviously aid in interpreting intelligently the 

 , outcome of such practical studies. 



"^ What is true of practical experimentation with farm animals is 



r^ equally true of scientific experimentation. An accurate knowledge of the 



food requirements of the experimental subjects is not infrequently a 



vital prerequisite to the correct interpretation of the results secured. 



Much of the German experimentation on the capacity of ruminants to 



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