280 THE CHEMISTRY OF CATTLE FEEDING 



ingredients from which they are derived is known. For 

 example, hay of average quality contains about 10 per cent, 

 of total nitrogenous matter, and decorticated cotton cake 

 about 40 per cent., but it would be quite wrong to assume 

 that 4 Ibs. of the former are equal to i Ib. of the latter. 

 In hay a considerable amount of the total nitrogenous matter 

 is not true protein; only about half of the latter is digestible, 

 and of the digestible portion a considerable amount is 

 expended in the work of digestion ; whereas in the cake 

 it is practically all true protein, a much larger percentage is 

 digestible, and little or none is spent in the work of digestion. 

 If, therefore, any of the nitrogenous matter of a cake is 

 derived from hay, it will be of much inferior value to that 

 derived from seeds. 



Apart from these considerations, it is obvious that the 

 suitability of a cake for any particular purpose must depend 

 to a very large extent upon the kinds and quantities of 

 the other foods that are used along with it. If the per- 

 centages of digestible nutrients in a cake and in the other 

 foods to be used in conjunction with it are both known, 

 the foods can be adapted to each other by the methods 

 described in Chapter XIV. ; but in the absence of such 

 information, it is impossible for the farmer to exercise any 

 scientific control. He must be guided merely by the instinct 

 of the animals and the length of his purse. 



Industrial By-products. The more important industries 

 in which by-products suitable for the nutrition of farm-stock 

 are obtained are malting, brewing, distilling, and the manu- 

 facture of starch and sugar. The by-products of the flour 

 mills and oil mills have already been described. The nature 

 of the substances and the probable variation in quality, apart 

 from deliberate adulteration, is best shown by a brief review 

 of the methods by which they are produced. 



Malt Dust. This product, sometimes called " coombs " 

 or " cummings," consists of the dried sprouts of barley grains. 

 The tissues are very young, and in the fresh condition would 

 almost certainly prove extremely soft and readily digestible. 

 They are, however, always dried in order to separate them 



