FEEDS FOR ANIMALS 67 



is because they have the feeds in mind and not the substances 

 of which the feeds are made. 



The process of digestion then is simply one of breaking up 

 a feed into its component parts. What the animal wants is 

 protein, carbohydrates, fat, mineral matter, and water. 

 These are the materials or compounds of which feeds are 

 made. They are called nutrients. 



PROTEIN 



Protein is the substance used by the animal for growth. 

 It is a chemical compound made up of carbon (C), hydrogen 

 (H), oxygen (O), nitrogen (N) and sometimes sulphur. These 

 latter substances are called elements. 



Carbon is a solid substance and in its purest form is found 

 in the diamond and also in graphite from which the lead of a 

 lead pencil is made. Coal also is largely composed of carbon. 

 This element also makes up a large part of all plant and ani- 

 mal or organic growths. 



Nitrogen is a gas and is one of the elements of air. The 

 other important gas in this mixture, the air, is oxygen. This 

 is the substance that is needed to make a fire burn or to make 

 the food burn in the body of an animal. A bale of hay burned 

 in the body of an animal by metabolism gives off just as much 

 heat as when burned by means of fire in a stove or in the open 

 air. Nitrogen is an inert gas and is mixed with the oxygen 

 to make air. 



Hydrogen as such is also a gas, but when hydrogen and 

 oxygen are put together in the right proportions chemically, 

 two parts of hydrogen to one of oxygen, it makes water. 

 Oxygen however, weighs about sixteen times as much as 

 hydrogen. 



When these four substances — carbon, hydrogen, oxygen 

 and nitrogen — are chemically combined the result is protein. 

 This protein is used by the animal for growth and also to some 

 extent for maintenance. 



Growth. — The lean meat, the glands, hide, hair, horns and 

 hoofs of the animal are made up largely of protein. When 

 the animal body is making these tissues in its body it is said 

 to be growing. From this it is very obvious that if the 



