2:>4 A Manual of Veterinary Physiology. 



Digestibility of Food. 



From a physiological point of view we understand by the 

 digestibility of food, that a portion of each of the proximate 

 principles it contains is capable of being absorbed. Every 

 food contains albumin or proteid, fat, carbo-hydrates, 

 and salts. Of each of these there is a distinct proportion 

 absorbed, and the remainder rejected and excreted with the 

 fseces. The number which represents the quantity absorbed 

 is spoken of as the digestive co-efficient. In each food 

 there is a distinct co-efficient for each proximate principle. 

 The methods employed by which these results have been 

 obtained, have been to feed animals on food of known com- 

 position and analyse the excreta ; the difference between 

 the albumin, fat, starch, sugar, cellulose, etc., taken in by 

 the mouth, and that rejected from the body by the f.eces, 

 is the measure of the amount digested (see table, p. 224). 



The digestibility of a food depends upon its age, growth, 

 mode of preparation, and condition. Well-saved hay, for 

 example, is better digested than hay which has been 

 washed by rain. The admixture of other substances with a 

 food also affects its digestibility ; the addition of starch or 

 sugar to a diet of hay and straw, if it exceeds 10 per cent, 

 to 15 per cent, of the dry forage, decreases its digestibility ; 

 small quantities of oil aid digestion, large quantities retard 

 it. I have found that the addition of oats to a ration of 

 hay increased the amount of hay digested. 



Contrary to expectation, experiments made by the French 

 and Germans have shown that neither crushing oats nor 

 cutting hay increases the proportion assimilated by the 

 system; it is certain that, as a practical matter, both these 

 methods of preparing food for horses are highly appreciated 

 in this country, and I think with good reason. I have been 

 led to regard 'J lbs. of crushed oats as equal t<» 9| Lbs. to 

 10 lbs. of uncrushed ; these results were not obtained as 

 the result of scientific investigation, but as a matter of 

 observation. 



Experiments have shown that the same amount of 

 proximate principles are not digested by all classes of 



