120 SWINE 



tity of this, when taken in as a feed from external sources, 

 the nutrient carbohydrate is the principal source of 

 energy. 



The amount of protein in the carcass of a hog varies 

 somewhat with the condition of the animal, but not to the 

 same extent as the amount of water present. As the hog 

 grows, especially during the growing period as contrasted 

 with the fattening period, he is, under normal conditions, 

 always adding protein to his body. At the same time 

 he is adding other tissues, particularly fat. But during 

 the fattening period he will add relatively more fat, and 

 consequently the fatter the hog the smaller is the relative 

 amount of protein contained in the same. 



In general the carcass of a hog contains from 12 to 15 

 per cent of protein. The principal protein tissues are 

 the lean meat or muscle tissues. Besides this, however, 

 protein is quite widely distributed throughout the body, 

 such as in the fluids of the body, the cells which contain 

 the fat, the bones, and the hide, hair and horns. All parts 

 of the body, then, contain protein, but the muscle or 

 the lean meat is made up primarily of protein. 



In order to allow a pig to build up the protein part of 

 his body he must have protein as a food. Protein 

 metabolism cannot be supplied by any other food 

 nutrient. This is one of the laws of nature ; consequently 

 a hog may be allowed to starve to death with a full 

 stomach. That is, if he were given all the carbohydrate, 

 all the fat, all the water, and all the ash or mineral mat- 

 ter that he could eat, he would still starve to death un- 

 less he had protein to supply the protein metabolism or 

 the part of his mechanism that has to do with the con- 

 struction and maintenance of lean meat or protein tissues. 

 To expect a hog to live and thrive without protein would 



