VALUATION OF FEEDING STUFFS 221 



oxen, in these terms, are 6 Ibs. of starch equivalent, the 

 quantity of the food required can be ascertained by a simple 

 calculation. Thus, 6 -f- 0*86 = 7 Ibs. is the quantity. Of 

 course, if the food does not contain the necessary amount of 

 protein, the balance must be derived from other sources ; and 

 in that case the rations must be compounded in the manner 

 described in Chapter XIV. 



It was pointed out in connection with the system of " feed- 

 ing standards," referred to in previous chapters, that confusion 

 must result if the thermic value of one food be added to the 

 dynamic value of another ; and that the difficulty is not over- 

 come by expressing these values in terms of equivalent amounts 

 of starch or other nutrient. This, however, does not apply to 

 the starch values. The amount spent in the work of digestion 

 is deducted in all cases. The results are therefore strictly 

 comparable and can, if necessary, be added together. Feeding 

 standards expressed in terms of starch equivalents are not, 

 therefore, open to the same objections as those which show 

 merely the total amounts of digestible nutrients required. 



It should be recognised, however, that the system of starch 

 equivalents has limitations. These have not always been pro- 

 perly appreciated, and the practical advantages appear to have 

 been overestimated. It has been said, for instance; (i) that 

 the starch value sums up all the properties of a food and 

 expresses them by a single number; (2) that it forms the only 

 reliable basis for the comparison of foods of different kinds ; (3) 

 that any two foods can be substituted for each other in the 

 proportion of their starch equivalents without altering the 

 nutritive value of the ration as a whole. 



It may be pointed out, however, (i) that two numbers are 

 always required one for the protein and one for the non- 

 nitrogenous nutrients ; and in the system of starch equivalents, 

 a third the amount of total organic matter must also be 

 known ; (2) foods of different kinds cannot be compared on any 

 basis whatever without reference to the purpose for which they 

 are to be used, and those which have the highest starch values 

 are not in all cases the most suitable or economical ; (3) the 

 starch equivalent of meadow hay is about thirty, and that of 



