60 PRINCIPLES OF FEEDING FARM ANIMALS 



coefficients of digestibility are approximately correct, and 

 they must be used until methods of separating the food 

 residues from the other constituents of the feces are worked 

 out. 



There are many feeds which cannot be fed alone to cer- 

 tain classes of animals. For example, such feeds as corn 

 and oats cannot be fed to cattle, sheep, and horses unless in 

 combination ^\^th some roughage, as hay or straw, while 

 such feeds as tankage and oil meal cannot be fed alone to 

 hogs. Thus it is impossible to determine directly the coef- 

 ficients of digestibiUty of many of the concentrates. In 

 determining the digestibiUty of such a feedingstuff, it is 

 fed with a feed whose coefficients of digestibiUty have been 

 determined previously. The total consumption of each 

 nutrient {i.e., from the entire ration) and the total amount 

 of each nutrient excreted in the feces is determined in the 

 usual manner. The amount of each nutrient digested then 

 iS obtained by subtracting the amount of each nutrient 

 excreted from the total amount of the corresponding nu- 

 trient consumed. The amount of digestible nutrients con- 

 sumed from the feedingstuff whose digestibiUty is known is 

 calculated by multiphdng the amount of each nutrient con- 

 sumed from that feedingstuff by its previously determined 

 coeffi?ient of digestibility, and dividing the result by 100. 

 Subtracting these results from the total amount of each 

 respective nutrient digested, the amount of each nutrient 

 digested from the other feed is obtained. The coefficient 

 of digestibiUty then is calculated as before. 



For example, in a digestion period of seven days a hog 

 was fed a ration consisting of ground corn and tankage, the 

 coefficients of digestibility of the corn being determined in 



