DIGESTION AND DIGESTIBILITY 29 



must be palatable and appetising for the digestion to be 

 at a maximum, so that mouldy or dirty fodder, even 

 when mixed in small amounts with sound fodder, lessens 

 the digestibility of the whole. 



Another factor affecting digestion is the combination 

 of foods supplied in the ration. For example, an excess 

 of starchy matter relatively to protein and fats will 

 depress the digestibility of the whole ration, so that if to 

 a fairly balanced ration 2 lbs. of dry starch be added, 

 it will be found that less protein and less fat are being 

 digested than before. Thus the addition of a food like 

 potatoes to a diet poor in protein would further depress 

 the digestibility of each component of the whole ration. 

 If, however, a further addition of protein material were 

 now made, this would improve the digestibility for each 

 ingredient. Thus it has been demonstrated that any 

 excess of carbo-hydrate over about 10 parts to 1 of 

 protein means that some of the digestible part of the 

 ration fails to be digested, and is passed out with the 

 excreta. Digestion is also affected by the total quantity 

 of food supplied. A large ration, in excess of the 

 requirements of the animal, is not digested to the same 

 extent as a smaller one sufficient for the animal's needs ; 

 and the greater the excess, the more is digestion 

 depressed. Thus overfeeding is extravagant, because 

 the excess over the requirements is not serving any 

 useful purpose, and also because, of the food supplied, 

 a smaller proportion is being absorbed and used in the 

 overfed animal than in one just sufficiently fed. For 

 digestion to be satisfactory it is necessary for the horse 

 to have a certain number of hours at rest in the stable. 

 Experiments seem to show that ordinary work has little 

 detrimental effect on digestion, but fast work does inter- 

 fere with it. This is in agreement with practical 



