330 



NUTRITION OF FARM ANIMALS 



the nitrogen balance of the horses was determined during six 

 of the periods. The following table shows the amounts of 

 protein and of non-protein nitrogen digested in each period, 

 the urinary nitrogen, and the small losses in epithelial tissue 

 (epidermis, hoofs, hair, etc.) : 



TABLE 61. NITROGEN BALANCE OF HORSES 



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

 digestible 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 was 235 grams, or 0.59 

 Ib. per 1000 pounds live weight, equivalent to about 0.50 Ib. 

 true protein. 



419. The optimum of protein. The data of the foregoing para- 

 graphs seem to indicate a striking uniformity in the minimum 

 protein requirement of the principal species of domestic animals 

 with perhaps the exception of the hog when mature, 0.4 to 0.6 

 Ib. per 1000 pounds live weight apparently sufficing to main- 

 tain nitrogen equilibrium under favorable conditions. 



It should be clearly understood, however, that this figure 

 represents a more or less accurately determined limit. It pur- 

 ports 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 minimum, using some of it to increase 



