NUTRITION 105 



with thorough mastication tends to reduce the digestibility 

 of the food. On the other hand, mechanical grinding, which 

 ruptures the cells and exposes a larger surface to the action of 

 the digestive juices, perceptibly increases the digestibility of 

 the harder fodders. Complete disintegration increases the 

 digestibility very largely. 



The percentage of cellulose in vegetative organs increases 

 very rapidly as the plants develop. As a result of various 

 physiological and chemical changes it soon becomes harder 

 and more fibrous, and the digestibility both of this and other 

 constituents is reduced. For example, the digestibility of the 

 total organic matter in grass cut at the middle of May is about 

 78 per cent., a month later it is reduced to about 65 per cent., 

 and at the end of June, when the grass is cut for hay, it is 

 only about 60 per cent. 



The digestibility of the constituents of seeds of plants 

 grown under normal conditions is high and fairly constant. 

 In fodders which consist of the vegetative organs of plants the 

 coefficients of digestibility are lower and much more variable. 

 Apart from substances which are by-products of industrial 

 processes, the widest variations are found in preserved fodders, 

 e.g. hay, silage, etc. Any losses due to soaking with rain, or 

 to fermentation, fall most heavily upon the soluble and readily 

 digestible portions. The average coefficients of digestibility 

 for such products are not, therefore, of much value for par- 

 ticular samples unless all the circumstances are known. 



When the food consists of a single substance of a suitable 

 kind, the digestibility is independent of the amount of the 

 ration. For example, the digestibility of the organic matter 

 of hay was found to be practically the same about 60 per 

 cent. when oxen were fed upon it at the rate of 15, 20, and 

 25 Ibs. per day, respectively. 



The same is true also of mixed fodders, provided the 

 relative proportions of the different constituents are properly 

 balanced ; but excess of any one ingredient affects the digesti- 

 bility of all to a considerable extent. The addition of fodders 

 rich in carbohydrates especially those of a readily digestible 

 nature, e.g. starch and sugar to a fodder poor in protein 



