THE HORSE AS A MOTOR 29 



these two classes have little energy value. Of the other three 

 classes, the fats are usually unimportant in feeds for horses, 

 being present in relatively small amounts. They are, however, 

 rich in heat-producing value, being about two and one quarter 

 times as valuable in this respect as the proteids or carbo- 

 hydrates. The fats consist of true vegetable fats and oils, such 

 as cottonseed and corn oil, waxes, and various coloring matters 

 in plants. 



The muscular tissue of the body is largely composed of 

 proteids or nitrogen-bearing compounds. A certain amount 

 of these compounds must, of course, be present in the feed, 

 in order to maintain the body at its normal state. In the 

 absence of fats or carbo-hydrates, the proteids may be used 

 for energy. However, since they are usually much more 

 expensive than the carbo-hydrates, the most economical 

 rations contain only sufficient amounts of various proteids to 

 maintain the body. The bulk of the energy supplied to the 

 work horse should come from the carbo-hydrates. This class 

 includes the various sugars and starches, also the crude fiber 

 or cellulose which give strength to the structure of the plant. 



The crude fiber is less digestible than the sugars and starches, 

 but is equal to them in total heat value. Thus the animal, 

 in a sense, is less efficient than a steam engine, which can make 

 use of the entire plant, as, for instance, when straw is burned 

 underneath a steam boiler. The horse at hard work has less 

 opportunity properly to chew and digest the rough, coarse 

 hay and fodder supplied, consequently wastes a much larger 

 proportion than when at rest. On this account it is probable 

 that the average farm horse receives much larger amounts of 

 hay than he can economically use. Even at rest the horse is 

 much less efficient than cattle or sheep in making use of the 

 coarse material, such as hay and straw. The latter animals 

 have greater capacity in the alimentary canal, consequently 

 retain the food from 50 to 100 per cent, longer than the horse. 

 This allows extensive fermentation to occur, consequently 



