UTILIZATION OF FOOD 



423 



Productive Value of Feeds. The substances thus mentioned 

 represent the various groups of constituents of a feeding- 

 stuff. 1 Kellner determined the composition and digestibility of 

 a number of feeding-stuffs, and calculated the quantity of fat 

 which each could produce, based upon the values given in the 

 preceding table for the digestible nutrients. The following is an 

 example of the method of calculation used : 



COTTONSEED MEAI,. 



Thus 100 grams of cottonseed meal should produce 20.07 

 grams fat under the conditions given. We will term this the 

 productive value. 



If the value of a feeding-stuff for producing fat is in propor- 

 tion to the quantity of digested nutrients present, i. e., if the 

 digested nitrogen-free extract etc., of one feed has the same 

 value as that of any other (as has heretofore been assumed), then 

 the above method of calculation should be correct. 



The results of a number of experiments and calculations are 

 given in table on following page: 2 



The calculated quantity of fat is, in many cases, much greater 

 than that actually found by experiment. That is to say, the pro- 

 ductive value of different kinds of feeds is not necessarily in pro- 

 portion to their content of digestible nutrients. 



1 See also Hagemann, Exp. Sta. Record 10, p. 907. 



1 After Kellner, Die Ernahrung d. Landw. Niitztiere, p. 163. 



