THE FEEDING OF ANIMALS 43 



as a source of energy. The amount appropriated as fat and 

 energy depends on the quantity fed to the animal. A pound of 

 protein, however, is worth more than a pound of carbohydrates 

 on the market. Then to use protein substances largely as a 

 source of fat and energy, where cheaper substances would do 

 fully as well and perhaps better, as we shall presently see, is not 

 economical. On the other hand, if the protein in the food is in- 

 sufficient fully to supply the needs of the animal, the very best 

 development will not be attained. The economy of feeding, 

 therefore, depends largely on the balance between the protein 

 on the one hand and the remaining nutrients on the other 

 hand. It is to secure sufficient protein and yet not to use it waste- 

 fully that so much attention is given to the proper balancing of a 

 ration. 



Carbohydrates. — Carbohydrates are used to maintain heat 

 and in the production of fat. Formerly it was thought that 

 carbohydrates are used for that purpose only, but it is now 

 well established that the animal fats may have their source 

 in 'the carbohydrates. Again, experiments with milk cows 

 show clearly that milk-fat may also be derived from carbo- 

 hydrates. The fact that carbohydrates can be used as heat- 

 producersand as fat-formers, connected with their ease of digestion 

 and cheapness of production, tends to magnify the importance 

 of this group of nutrients. 



Fat. — Fat, like carbohydrates, serves as a source of heat and 

 of animal fat. The differences are that the supply of carbohy- 

 drates is much the larger, and the heat value of a similar weight 

 of fats much the greater, — as we have already seen 2^ times as 

 great. Moreover, there seems to be experimental evidence 

 showing vegetable fat to become deposited in the animal without 

 change, whereas fat formed from carbohydrates involves com- 

 plex transformation. 



From the foregoing statements, it is evident that the water 

 taken into the animal serves as the water of the animal body. 



