114 NUTRITION OF FARM ANIMALS 



of previous feeds and also of establishing as uniform a rate of 

 excretion of feces as practicable. In the case of ruminants, such 

 a preliminary period should extend over one or two weeks, while 

 with swine it may be made somewhat less. In the succeeding 

 digestion experiment proper, the same feeding is continued 

 and the feces are collected quantitatively for a number of days 

 (seven to ten or more), in order to eliminate the error due to the 

 irregularity of the excretion from day to day. From the 

 weights of feeds and feces and their composition as determined 

 by analysis, the digestibility is computed as illustrated in the 

 following paragraphs. 



160. Example of a digestion experiment. A steer was fed 3.7 

 kilograms of clover hay per day for three weeks. During the last 

 ten days of this time, the average weight of the daily feces was 5.662 

 kilograms. Samples of each were analyzed and found to contain 

 the following percentages of dry matter. 



Clover hay 84.97 P er cent 



Feces 22. 36 per cent 



The 3.7 kilograms of hay, therefore, contained 3.144 kilograms of 

 dry matter while the 5.662 kilograms of feces excreted contained 

 only 1.267 kilograms of dry matter. The difference, 1.877 kilograms, 

 which did not appear in the feces, is regarded as having been digested 

 by the steer. This amount is 59.7 per cent of the 3.144 kilograms 

 eaten; we say, then, that the percentage digestibility of the dry 

 matter of this hay was 59.7 and this number is sometimes called its 

 "digestion coefficient." 



In precisely the same way the percentage digestibility of each in- 

 gredient may be computed from the results of analyses of the hay 

 and of the feces, which in this case gave the following results : 



HAY FECES 



% % 



Water 15.03 77.64 



Ash 5.49 1.92 



Protein 10.24 3.13 l 



Non-protein 1.36 



Crude fiber 28.61 9.29 



Nitrogen-free extract 36.98 7.50 



Ether extract 2.29 0.52 



100.00 100.00 



1 All the nitrogen of the feces is here assumed to exist in the form of protein, an 

 assumption which, as will appear later, is far from being true (166), but which 

 does not affect the method of computation. 



