DIGESTION AND DIGESTIBILITY 25 



process is that whereby cellulose and fibre are broken 

 down and made soluble, largely as a result of the action 

 of the immense numbers of bacteria which this part of 

 the bowel contains. In cattle, sheep, and goats (rumin- 

 ants), the digestion of cellulose is much more efficient 

 than in the horse, and, moreover, it takes place in the 

 first stomach, or rumen. The consequence is that the 

 fibrous cell walls, husks, and stems, are broken down 

 and their contents set free before true stomach and 

 small intestine digestion have taken place, and so no 

 starches, proteins, and fats, are allowed to escape diges- 

 tion because of being enveloped in a protecting layer of 

 cellulose. In the horse, on the other hand, cellulose 

 digestion occurs after stomach and small intestine 

 digestion, and thus it happens that a woody or fibrous 

 envelope often prevents nutritive starches, sugars, 

 proteins, and fats, from being acted on by the digestive 

 juices, and these nutrient substances are passed out as 

 waste material with the excreta. Thus the presence of 

 a large percentage of cellulose or woody fibre in any food 

 material renders it unsuitable for horses ; for, even though 

 it may show a good chemical composition on analysis, the 

 animal is unable to digest a large part of the fibrous cell 

 walls, and, hence, much of the nutritive material passes 

 out unchanged and unused. 



It must not be supposed that a food with no cellulose 

 or fibre would be suitable for the horse, for the fibre adds 

 bulk to the food, and there is an intimate relation 

 between the capacity of the intestines and the required 

 bulk of food. The bowel must be sufficiently full, 

 because the passage of material along the tube depends 

 upon muscular contraction, which is only set up by the 

 contact of a certain bulk of food on the sensitive lining 



