THE FEEDING OF ANIMALS 41 



classed as most readily digestible. Fiber or crude fiber consti- 

 tutes the tough woody part of plants. The stems of all plants 

 contain more fiber than does the leafy part. Variation in the 

 digestibility of foods depends largely on the amount of crude 

 fiber, which is mostly insoluble and hence largely indigestible. 

 Crude fiber is the least valuable of the four nutrients, because 

 of its indigestibility. Young plants contain less crude fiber 

 than plants that have matured and formed seeds, and hence are 

 more digestible. 



Fat. — Plants also contain fat or oil. It occurs in largest 

 quantities in the seed, and varies widely, running less than 2 per 

 cent in rye to 30 and 35 per cent in flaxseed. Fats like carbo- 

 hydrates contain carbon, hydrogen, and oxygen, but no nitrogen. 

 The oil content of food is determined by extracting the fat by 

 ether; hence in tables giving composition of food the fat is often 

 designated as ether extract. A given weight of fat will develop 

 2\ times as much heat energy as an equal weight of carbohy- 

 drates. If we multiply fat, therefore, by 2^, it reduces it to the 

 starch or carbohydrate equivalent. Fats are not so readily di- 

 gested as nitrogen-free extract. 



Functions of various food materials 



A knowledge of the function of the various food materials 

 will enable one to choose and balance a ration more economically, 

 and to adapt it to the needs of the animal. A very satisfactory 

 ration for a race horse may be entirely inadequate for a dairy 

 cow. 



Water. — The water of the food takes the place to a certain 

 extent of the water that an animal would otherwise drink. In 

 the case of food containing a large amount of water, the total 

 consumption of water by the animal will be greater than other- 

 wise. Watery foods will not, however, satisfy the animal in this 

 respect, as it will still drink water. In many cases the large 

 consumption of water is of advantage to the animal; this is 



