I9i I-] 



Concentrated Feeding-stuffs. 



223 



digested from the food, and only the balance is available 

 for the productive purposes of the feeding. The tougher and 

 more indigestible the food is, the greater will be the amount 

 of digestible material diverted to unproductive purposes, and 

 the lower will be the direct value of the food to the animal. 

 In other words, if foods of very different character (e.g., maize 

 and undecorticated cotton cake) are compared, it is necessary 

 to know not only the amount and character of the digestible 

 matter in the food, but also its "availability" to the animal. 

 The chief determining factor is the proportion and character 

 of the crude fibre in the food, and in the case of all foods that 

 are not markedly rich in crude fibre, no serious error will be 

 committed if the digestible nutrients are regarded as fully 

 "available." In the case of fibrous foods, however, the value 

 of the digestible matter will be considerably overrated if the 

 presence of an abundance of crude fibre is not taken into 

 account (see later). 



Manurial Ingredients in Foods. 



All foods contain appreciable quantities of valuable 

 manurial ingredients, notably nitrogen, phosphates, and 

 potash. These ingredients are voided to a considerable 

 extent in the solid and liquid excrements of the animals 

 which consume the food. In the case of full-grown fattening 

 animals or working horses practically all the fertilising in- 

 gredients are recovered in this way, but in the case of young 

 animals and cows in milk the proportion recovered will be 

 lower. The proportions of nitrogen, phosphates, and potash 

 present vary greatly in different foods, and the value of the 

 manurial residues arising from the consumption of equal 

 weights of the foods varies accordingly. This fact must be 

 taken into account in comparing the cost of different foods, 

 since the real cost of a foodstuff to the farmer is obviously 

 the price less the manurial value. 



The latter value can only be assessed roughly and is subject 

 in practice to great variations. For comparative purposes, 

 however, the values given in the Table on p. 225 may be used. 



Comparative Values of Foods. 



Attempts have frequently been made to devise a satisfactory 

 system of direct valuation of feeding-stuffs on lines com- 



