290 THE FEEDING OF ANIMALS 



regarded as the economical one to purchase. This method 

 seems to be absurd, for it is an assumption that the 

 nutritive value of the carbohydrates and fat in commer- 

 cial foods may be ignored. The argument is that the 

 farm furnishes carbohydrates in abundance, and that 

 commercial products should merely serve the purpose of 

 reinforcing the protein-supply. If the carbohydrates of 

 the farm have no selling value then this argument has 

 some force, but this is ordinarily not the case. When 

 starch and similar compounds must be purchased as a 

 necessary accompaniment of protein, thus causing a sur- 

 plus of carbohydrate food, certainly hay, oats, corn, 

 barley, or some other home product may be sold to 

 relieve this surplus. 



387. Feed values based on feeding experiments. 

 Many practical feeding experiments have been con- 

 ducted for the purpose of comparing the different grain 

 products as foods for the various classes of animals. Useful 

 facts have been reached in this way, especially as to the 

 greater adaptability of some materials than others for a 

 particular species. But experiments of this kind cannot 

 be relied upon to fix relative values of feeding-stuffs for 

 milk production, beef production, or for any other pur- 

 pose. This is so, first of all, because the errors of such 

 tests are so large that we cannot regard their apparent 

 outcome as establishing constants. Again, the problems 

 involved are too complex and the effect of a given ration 

 too dependent upon variable conditions, to allow logical 

 conclusions from such experimental data. The difficul- 

 ties of the situation will be made clear to anyone by a 

 careful study of the whole mass of data resulting from 

 feeding tests. Differences appear, some of which are con- 

 sistently in one direction, especially in comparing nitrog- 



