384 



NUTRITION OF FARM ANIMALS 



TABLE 83. PERCENTAGE OF FEED PROTEIN RETAINED FINGERLING 



With advancing age, a relatively smaller retention is observed. 

 Thus Neumann obtained for calves 40 to 70 days old percentages vary- 

 ing from 38.7 to 48.3, and Tschirwinsky, experimenting on pigs 100 

 to 120 days old, observed a retention of 20.7 to 33.6 per cent of the 

 digested protein. With still older animals a yet smaller percentage 

 retention has been observed, diminishing to nearly zero with fully 

 mature animals. 



467. Does not measure utilization. On the basis of this 

 greater percentage retention it has been customary to say that 

 the utilization of feed protein is high in the case of the young 

 animal and diminishes rather rapidly as it grows older. This 

 statement is made essentially from a commercial standpoint 

 and in that sense it is true. Only the growing animal is capable 

 of using any large amount of feed protein to increase its stock 

 of body protein and the ability to do this is the more marked 

 the younger the animal. 



The percentage retention of the feed protein, however, is 

 necessarily variable and neither affords a measure of the effi- 

 ciency with which the animal converts it into body protein 

 nor permits a comparison of that efficiency at different ages. 

 The comparison is disturbed by two important factors to which 

 attention has been especially called by Fingerling, 1 viz., the 

 influence of the total amount of protein supplied and the effect 

 of a deficient energy supply. 



468. Influence of protein supply. As has already been 

 implied, growth is primarily dependent upon biological factors. 

 The feed supplies material for growth but does not determine 

 its maximum rate. The rate of increase of protein as formu- 

 lated in the previous section (463) represents (so far as the 

 results are trustworthy) the capacity of the animal for protein 



1 Landw. Vers. Stat., 74 (1910), i. 



