THE OPTIMUM OF PROTEIN. 



97 



experiments are on record which demonstrate the sufficiency of this 

 amount as a maintenance ration. 



the: horse. 



In the experiments by Grandeau and Le Clerc described on pages 

 62-63 the nitrogen balance of the horses was determined during 6 of 

 the periods. The following table shows the amounts of protein and 

 of nonprotein nitrogen digested in each period, the urinary nitrogen, 

 and the small losses in epithelial tissue (epidermis, hoofs, hair, etc.) : 



Nitrogen balance of horses — Grandeau and Le Clerc. 





Horse No. 1. 



Horse No. 2. 



Horse No. 3. 



January, 

 1884. 



April, 1884. 



November, 

 1883. 



May, 1884. 



December, 

 1883. 



March, 

 1884. 



Digested: 



Protein nitrogen 



Nonprotein nitrogen 



Total nitrogen 



Nitrogen of epithelial tissue . . . 



Urinary nitrogen 



Nitrogen gained 



Grams. 

 43. 19 

 1.20 



Grams. 

 34.29 

 - 1.01 



Grams. 

 38.94 

 - 3.23 



Grams. 

 34.22 

 10. 78 



Grams. 

 41.82 

 - 2.09 



Grams. 

 24. 72 

 - 4.58 



44. 39 



33. 28 



35.71 



35.00 



39. 73 



20.14 



1.46 

 35.17 

 7.76 



1.46 

 38.75 

 - 6.93 



1.46 

 30.70 

 3.55 



1.46 

 41.92 

 1.62 



1.46 

 37.62 

 .65 



1.46 

 32.70 

 -14.02 



Omitting the results upon horse No. 3 in March, when the diges- 

 tible protein was exceptionally low, the other five periods show an 

 average daily gain of nitrogen of 1.33 grams, while the average crude 

 protein digested (total N.X^.25) was 235 grams, equivalent to 0.59 

 pound per 1,000 pounds live weight. 



THE OPTIMUM OF PROTEIN. 



The data of the foregoing paragraphs seem to indicate a striking 

 uniformity in the minimum protein requirement of the principal spe- 

 cies of domestic animals when mature, 0.4 to 0.6 pound per 1,000 

 pounds live weight apparently sufficing to maintain nitrogen equilib- 

 rium under favorable conditions. 



It should be clearly understood, however, that this figure repre- 

 sents a more or less accurately determined limit. It purports to be 

 the amount below which the protein supply can not be reduced 

 without eventual protein starvation. The animal body, however, 

 may adjust itself to a wide range of protein supply above the mini- 

 mum, using some of it to increase the stock of protein in the body 

 and katabolizing the remainder as fuel material. An increase in the 

 protein supply above the minimum results, after a relatively short 

 time, in the maintenance of the body protein at a higher level. The 

 practical question in actual maintenance is far less in regard to the 

 8489°— Bull. 143—12 7 



