362 THE HORSE 



magnesia, potash, soda, iron, chlorine, and carbonic, sulfuric and 

 phosphoric acids. The ash of the food is the source of the mineral 

 matter of the animal body, and as such is of great importance. 

 Ordinary combinations of feeding stuffs, however, contain an 

 abundant supply of mineral matter for the use of the animal, so 

 it is not a matter of practical concern except as it has a bearing 

 on the mineral elements of fertility in the manure. 



Fats. This group embraces the materials which may be dis- 

 solved from a feeding stuff by ether. It includes, besides the 

 true fats, wax and coloring matter. Fat in the food may be either 

 stored in the body as fat, or burned to produce heat and energy. 



Carbohydrates. This term includes two groups, nitrogen-free 

 extract, such as starch, sugar, gum, etc., and fiber, or the woody 

 parts of plants. The former are quite freely digested, the latter 

 much less so, though fulfilling the same function to the extent it 

 is digested. The carbohydrates constitute the largest part of vege- 

 table foods. They are not stored in the animal body as such, but 

 are converted into fat or used (burned) to produce heat and 

 energy. 



Since the carbohydrates and fat serve nearly the same purpose 

 in the animal economy, they may, for convenience, be grouped 

 together. Experiments, however, have shown that fat is about 

 2/^ times as effective as a food as are the carbohydrates. Hence 

 it is customary to multiply the amount of fat by 2% to reduce it 

 to a "starch equivalent" before adding it to the amount of the 

 carbohydrates. 



Protein. The protein of foods, like that of the animal body, is 

 characterized by containing nitrogen. It, therefore, is frequently 

 termed "nitrogenous matter." The term albumenoids is sometimes 

 used to designate this group, though it more correctly implies 

 a certain class of protein substances. The function of protein 

 in the food is, first of all, to build up and repair the working 

 machinery of the body, and to supply protein for the produc- 

 tion of milk, wool, etc. No other food constituent can fulfil this 

 function. 



The importance of a sufficient supply of protein in the ration, 

 is, therefore, apparent. If in excess of the amount required to 



