41 



one gives up more materia^ to the body than the other, that is, is more 

 thoroughly digested, it must actually be more valuable than the other 

 material. The bulk of the substance of almost all feeding stuffs is 

 insoluble when eaten. Only material in solution can pass through the 

 walls of the stomach and intestines into the circulation and be utilized 

 by the body, therefore digestibility consists chiefly in rendering insol- 

 uble materials soluble. This is effected by the aid of digestive fer- 

 ments and also b}'^ bacteria. 



Digestion experiments are frequently made to learn how thoroughly 

 a given feeding stuff or i-ation is assimilated. The usual method is to 

 feed the material under consideration for a longer or shorter time, the 

 amount and composition being determined. From the total nutrients 

 consumed, the amount excreted and undigested in the feces is deducted, 

 showinpf the amount of each retained in the body. It is the usual cus- 

 tom to express the amounts digested in percentages, the results thus 

 obtained being termed coefficients of digestibility. 



The digestibilit}^ of a number of different feeding stuffs has been 

 tested with horses in this country and in Europe, although the number 

 of such experiments is much smaller than in the case of cattle and 

 sheep. The most extended series of American experiments with 

 horses was carried on by Patterson" at the Maryland Experiment 

 Station. In the table below the American and foreign digestion 

 experiments with horses are summarized. In a few cases values 

 obtained with ruminants are also included in the table, since no coef- 

 ficients of digestibilit}', obtained with horses, were available, and the 

 data were needed in computing the value of rations discussed later 

 (p. 48). 



Table 2. — Summary of coefficients of digestibility obtained in experiments with Jiorses. 



Kinds of fodder. 



Alfalfa, uncured 



Alfalfa hay 



Alfalfa (hay ^ stalks 



Alfalfa (hay) leaves 



Red clover hay 



Meadow hay, best quality 



Meadow hay, medium quality. 



Meadow hay, poor quality 



Meadow hay, average 



Timothy hay 



Corn stover b 



Ground corn shives 



Wheat straw 



Spelt straw , 



Corn silage c 



Carrots 



Potatoes 



Shelled corn 



Coefficients of digestibility. 



a Maryland Station Bui. 51. 



6 Coefficients of digestibility of corn fodder as fed to ruminants. 



c Coefficients of digestibility as fed to ruminants. 



