220 THE CHEMISTRY OF CATTLE FEEDING 



straws may be disregarded. At any rate, it is unnecessary to 

 employ factors calculated to the second decimal place. For 

 practical purposes, the mean value (2*3) may be used for the 

 fat in all concentrated foods, and the protein may be reckoned 

 equal to its own weight of starch. The starch equivalent of 

 concentrated foods may therefore be calculated simply by 

 adding the percentages of digestible protein, carbohydrates, 

 and fibre to 2-3 times the digestible fat, and then, as before, 

 making the necessary correction for what is spent in the work 

 of digestion. Thus, in the case of bran, the calculation would 

 be (10 + 45 + (3 X 2-3) } X 077 = 47-66. 



In order to utilise the starch equivalents of the foods to 

 advantage, it is necessary to know the requirements of the 

 animals in the same terms ; and it was shown in Chapter XII. 

 how these can be estimated. The term " starch equivalent " 

 was not employed, but it will 'be seen, on reference, that the 

 amounts of nutrients mentioned are in effect starch equivalents. 

 It was shown that oxen can form, at most, about 0-6 Ib. of 

 body fat from i Ib. of digestible fat, or equivalent quantities of 

 other nutrients, in the food ; but that sheep and pigs store up 

 a larger proportion. The requirements of these animals, in 

 terms of starch equivalents, are therefore less than those of 

 oxen for a given increase in live weight. This, however, does 

 not affect the determination of the starch equivalents of the 

 foods or the application of the same. There is no reason to 

 believe that there is any difference in the relative fattening 

 power of the several nutrients, though they have not the same 

 absolute power, for all animals. 



The starch values of the foods are not empirical numbers. 

 They are exact l scientific data, and afford a reliable estimate 

 of the fat-forming powers of the different foods. So far 

 as it relates to fattening as apart from maintenance the 

 system has withstood all criticism, and has proved useful in 

 practice. 



For example, if it be known that the starch value of maize 

 is 86 per cent, i.e. o'86 per Ib., and that the requirements of 



' The factors employed may call for revision or confirmation (cf. p. I2l), 

 but the soundness of the method is not open to question. 



