230 SCIENTIFIC FEEDING OF ANIMALS 



essential to be as economical as possible in the use 

 of the former, and to limit the quantity as far as is 

 practicable. It thus becomes necessary to find what 

 this limit is for the different species of animals, and 

 the purposes for which they are kept. 



Fats and carbohydrates can replace one another 

 both in the production of energy and of heat, and 

 I part of fat in a mixed ration can perform the func- 

 tions of 2-2 parts carbohydrate. A limit, however, 

 is placed upon the amount of fat in the food of 

 domestic animals, for more than i Ib. of fat per 

 1000 Ibs. live weight often diminishes the appetite, 

 and upsets the digestion in full-grown herbivora, 

 although young animals can generally take larger 

 quantities. In addition to this the fat of the food 

 often has a prejudicial effect upon the body, or milk- 

 fat, as has already been noticed, and attention will 

 also be drawn to this point later. For these reasons 

 the amount and kind of fat in the food require 

 particular attention. 



Amongst the other constituents of the food 

 to be considered are, in addition to the mineral 

 matter, the nitrogenous substances of a non-protein 

 nature, whose effect in the production of fat and 

 energy is included in the " starch equivalent " of 

 the feeding-stuffs. In view of what has already 

 been said (p. 65), it is not correct to reckon these 

 substances as proteins. It would, in many cases, 

 be a matter of indifference whether, in the calcu- 



