80 MAINTENANCE RATIONS OF FARM ANIMALS. 



in the amount of protein consumed, both per unit of weight and especially 

 per unit of gain, and concluded that the apparent excess of protein in some 

 cases must have served substantially for respiratory purposes. 



Of the numerous later and more specific investigations on herbivora in which 

 the nitrogen excretion has been determined, the following 1 may serve as an 

 example. Two sheep were fed in periods 1 and 7 a basal ration of hay and 

 barley meal. To this ration were added in the intermediate periods varying 

 amounts of nearly pure protein in the form of conglutin (of lupins) or of 

 flesh meal. A comparison of the nitrogen digested from the ration with the 

 urinary nitrogen shows that the latter increased and diminished substantially 

 parallel with the former. 



Protein kataboUsm, of sheep per day and head — Henneberg and Pfeiffer. 





Sheep I. 



Sheep II. 





Nitrogen 



Nitrogen 



Nitrogen 



Nitrogen 





digested. 



in urine. 



digested. 



in urine. 





Grams. 



Grams. 



Grams. 



Grams. 



Period 1 



8.18 



7.48 



7.81 



6.98 



Period 2 



17.86 



16. 82 



17.72 



16.37 



Period 3 



27.22 



25.75 



27.33 



23.94 



Period 4 



36.99 



32. 71 



37.07 



32.09 



Period 5 



26.76 



25.63 



26.91 



24.54 



Period 6 



17.62 



16.64 



16.94 



15.99 



Period 7 



8.34 



8.06 



8.00 



7.62 



UTILIZATION OF PROTEIN LIMITED. 



That the mere giving of protein food can not cause a large storing 

 up of protein is indeed sufficiently obvious from daily experience. 

 The muscles of the weakling can not be converted into those of the 

 athlete by feeding him upon a meat diet, nor the small man increased 

 in size by a very abundant protein supply. The protein tissues of 

 the mature animal have reached their natural limit of size and con- 

 sequently the capacity of the body to store up protein is limited, in 

 such an animal, beyond the minimum required to make good the 

 necessary katabolism in the cells protein can be utilized only to a 

 small extent in the body as protein, and it is therefore rapidly 

 katabolized, its nitrogen appearing in the urine as urea and other 

 familiar end products. Nor is the situation essentially different in 

 the growing or the milk-producing animal. While these animals are 

 able to utilize considerable amounts of feed protein, yet the limit of 

 this utilization is set by the normal rate of growth of the protein 

 tissues or the capacity of the mammary glands to manufacture the 

 casein and other proteins of the milk. Any surplus of protein over 

 the amount which can be used for this purpose is katabolized pre- 

 cisely as is a surplus over the very small demand of the mature 

 animal. 



1 Henneberg and Pfeiffer. Journal fiir Landwirtschaft, vol. 38, p. 215. 



