THE; NUTRIENTS AND THEIR FUNCTIONS 57 



quired in the processes of digestion in the digestive juices and 

 secretions. Iron is a necessary constituent of the blood. Nature 

 has provided for the very young animal by furnishing the 

 necessary mineral elements in milk. The young animal must 

 have mineral compounds to reach full development and the 

 mature animal requires ash for maintaining body functions. It 

 is fortunate that nature has supplied sufficient mineral matter 

 in most of the feeds that animals live on in this country. It is 

 only necessary to furnish mineral compounds when a diet con- 

 sisting chiefly of grain (such as corn) or prepared foods con- 

 sisting of parts of grain are fed. Animals cannot live without 

 mineral compounds. Such substances as common salt, wood 

 ashes, and precipitated chalk are sometimes fed in conjunction 

 with other feeds to supply the needs of growing animals. 



Functions of Protein. Protein as derived from plant sub- 

 stances is the main constituent of muscles, horn, hoof, hair, 

 ligaments, the tissues of the organs used in digestive processes, 

 and the working parts of the animal body. The protein com- 

 pounds are in reality the flesh formers. Protein bodies repair 

 the broken down tissues, help form blood, and milk. When 

 animals are fed protein in the right proportions they possess 

 vigor and look smart and lively. Without protein the animal 

 cannot live. Sometimes protein can be made to take the place 

 of fats and carbohydrates, but such substitution is not practicable, 

 as protein generally costs more than fats and carbohydrates. 

 Protein hardly ever performs the functions of fats and carbo- 

 hydrates unless these latter nutrients are lacking in animal's 

 food. The heat producing power of protein is about i% times 

 that of carbohydrates. As a heat producer fat is 2.25 times 

 greater than protein. The amount of body fat that protein pro- 

 duces is equal to one-half that which the fat of plant substance 

 produces. 



Functions of Fats and Carbohydrates. These nutrients per- 

 form the same functions and supply the fuel for the animal body. 

 They are heat producers and furnish the substances that keep 

 the animal warm. The fats and the carbohydrates also produce 

 fat in the animal body. The fats are not always changed in 

 5 



