PROTEIN REQUIREMENT OF CATTLE. 93 



In tne two periods in which there was a gain of protein by the animal the 

 crude protein available for maintenance, computed per 1,000 pounds live weight, 

 was: Pound. 



Cow No. 53, period 6 0. 58 



Cow No. 58, period 6 . 59 



In the four periods in which the loss of protein by the animal did not exceed 

 12.5 grams (2 grams nitrogen) the corresponding amounts were: 



Pound. 



Cow No. 10, period 6 0. 48 



Cow No. 53, period 4 . 43 



Cow No. 68, period 14 .44 



Cow No. 58, period 4 . 43 



These results are quite of the same order as those obtained by Kellner and by 



Armsby, while those on the two dry cows are much lower, with the exception of 

 a single result of Armsby's. (Experiment I, steer 2.) 



In drawing conclusions from the results recorded in the foregoing 

 pages, it is important to remember that what it is sought to determine 

 is the minimum protein requirement. As has been shown on previous 

 pages, an excess of feed protein above this minimum is, in the case of 

 the mature animal, substantially all katabolized, producing no mate- 

 rial gain of protein. The fact of an equality of income and outgo 

 of nitrogen upon a given ration of protein, therefore, while it shows 

 that the quantity consumed is sufficient for maintenance does not 

 show that a smaller amount would not suffice. What we have to 

 consider is the evidence of the experiments regarding the least 

 amount sufficient for maintenance. It is evident that this minimum 

 amount is relatively small, but it is also evident that the recorded 

 results do not suffice to fix with certainty the absolute minimum. 



The lowest recorded amounts per 1,000 pounds live weight upon 

 which nitrogen equilibrium was reached were 0.21 pound and 0.25 

 pound of crude protein in the Copenhagen experiments on dry cows, 

 while almost as small a quantity, viz, 0.27 pound crude protein or 0.23 

 pound true protein in Armsby's Experiment I, steer 2, fell very 

 little short of reaching nitrogen equilibrium. Aside from these 

 somewhat exceptional results, the lowest figures obtained per 1,000 

 pounds live weight were 0.43 pound crude protein and 0.38 pound 

 true protein, The maximum is found in Armsby and Fries' experi- 

 ment of 1903-4, viz, 0.96 pound crude protein and 0.84 pound true 

 protein, but it seems altogether probable that the animal in this 

 period was consuming a surplus of protein. If we omit these few 

 extreme results in either direction, the average and range of the 

 results of the other experiments are as follows : 



Average and range of protein requirements of cattle. 





Number of 



Protein requirement. 





experi- 





Maximum. 







ments. 



Average. 



Minimum. 







Pound. 



Pound. 



Pound. 



Crude protein 



19 



0. 55 



0. 75 



0.43 



True protein 



12 



. 52 



.63 



.38 



