FEEDS AND FEEDING 1 19 



mastication, the digestion in the simple stomach of the horse and pig and 

 in the three stomachs of the ruminants, and later in the small intestine, by 

 the pancreas, the liver and in the large intestine are discussed by the 

 animal physiologist, they are omitted from description here. It may be 

 said, however, that protein digestion is accomplished by the pepsin in the 

 stomach assisted by the trypsin and erepsin in the small intestine. The 

 digestion of either starch or sugars consists in converting them into 

 glucose, or glucose-like sugars and this transformation takes place 

 through the activity of the ptyalin in the saliva and by the amylase formed 

 in the small intestine, where the final carbohydrate digestion takes place. 

 The fats are digested by the secretions of the pancreas, where a fat splitting 

 enzyme lipase is formed which breaks fats into glycerin and fatty acids. 

 The bile secretions largely made up of alkaline salts react with the fatty acids 

 to form soaps, which with the glycerin is absorbed by the intestinal wall. 



Metabolism, or the process by which the digested nutrients of the 

 food are utilized for the production of heat and work, or built up with 

 the living matter of the body, or broken down and eliminated, is a sub- 

 ject for the consideration of the animal physiologist. 



Digestibility of Animal Foods. A large number of experiments have 

 been performed on animals of various kinds in order to ascertain the 

 digestibility of the feeding stuffs. The list of feeds, which have been used 

 in these experiments, is a long one. Out of these experiments a number of 

 important facts have been adduced. The average percentage of each 

 nutrient digested in a feeding stuff is termed the coefficient of digestibility, 

 or digestion coefficient, for that nutrient in the feed. The food is given 

 to the animal by weight and in these trials it is generally assumed that 

 all matter appearing in the feces has- escaped the action of the digestive 

 ferments and so represents the indigestible part of the food. Thus for 

 dent corn 90 per cent, of the total dry matter, 74 per cent, of the crude 

 protein, 57 per cent, of the fiber, 94 per cent, of the nitrogen-free extract, 

 and 93 per cent, of the fat is digestible. Feeds with little fiber have high 

 digestibility. To determine the digestible nutrients in any feeding stuff, 

 the total amount of each nutrient in 100 pounds thereof is multiplied by 

 the digestion coefficient for that nutrient. Thus 100 pounds of dent corn 

 contain 10.1 pounds of crude protein of which 74 per cent, is digestible, 

 which indicates that there are approximately 7.5 pounds of digestible 

 protein in 100 pounds of dent corn. 



Nutritive Ratios. As protein serves special uses in the body in dis- 

 cussions of feeds and rations the term nutritive ratio is used to show the 



