46 



MANUAL OF FARM ANIMALS 



the pig or horse. The food during its retention in the paunch 

 becomes thoroughly softened and undergoes some fermentation, 

 then it is re-chewed, — called chewing the cud, — and swallowed. 

 The stomach of the horse and pig is a single sack and has not 

 nearly so much capacity. 



The varying length of intestines and capacity of stomach 

 in farm animals is illustrated in the following table : — 



Length of intestines and capacity of stomach of farm animals 



It requires three to four days for food to pass through the di- 

 gestive tract of farm animals. Since animals of the same class 

 and in good health are fairly uniform in the amount of material 

 they extract from a given class of food, it is practicable to 

 make digestion trials to determine the amount of the various 

 food materials digested and to use these figures as a basis of com- 

 putation for all animals of the same class. 



Digestible nutrients. — Digestible nutrients are those parts of 

 food materials that are digested and appropriated to the ani- 

 mal's use. 0\ir knowledge of the amount of the food materials 

 that are digested is based on experimental data, and while not 

 absolutely accurate, is sufficiently so for practical purposes. 

 The method of determining the digestible nutrients is as fol- 

 lows : The animal is fed for a sufficient length of time on a 

 certain food or combination of foods, so that the digestive or- 

 gans contain only the food under test. Then for a certain length 

 of time the animal is fed a carefully weighed allowance of some 



