BUILDING MATERIAL. 125 



One important consideration in connection with deter- 

 mining coefficients of digestibility is the manner in which 

 the different feeds are used for which the coefficients are 

 to be determined. This is usually done by either feeding 

 a particular feed separately or by feeding several feeds 

 in combination. If the feeds are fed separately, then the 

 coefficients of digestibility for the various nutrients of 

 the feed are as already stated, namely, the total quantity 

 of dry matter passed out in the feces is to be subtracted 

 from the total quantity eaten. This remainder divided 

 by the total quantity eaten is the per cent digested, or the 

 coefficient of digestibility. This can be done with a num- 

 ber of feeds, such as corn and other ordinary grains, but 

 it cannot be done in a case where roughages or where 

 nitrogenous concentrates are ' fed. Roughages are not 

 sufficiently palatable to be used as a single feed. Nitrog- 

 enous concentrates are so rich in protein and contain so 

 little carbohydrate that a pig cannot be fed on such a 

 feed alone. In order to get the coefficients of digestibility 

 then for feeds like these, it is necessary to feed them in 

 combination with other feeds. 



In such cases corn, or some other feed that can be used 

 singly, is fed to the pig first as a single feed and the co- 

 efficients of digestibility are determined for it. The corn, 

 or whatever other feed may be used in such a process, is 

 called the basal ration. Following this a feed that can- 

 not be fed alone as, for instance, soy-beans, is fed in con- 

 nection with the corn. The coefficients -of digestibility 

 for soy-beans are then calculated. The coefficients that 

 were obtained when corn alone was used are applied to 

 the corn part of the combined ration which determines 

 what part of the feces of this ration should be accredited 

 to the soy-beans. This then is subtracted from the total 



