THE METHODS OF DETERMINING THE DIGESTIBILITY OF 



FEEDING STUFFS. 



Dr. O. Keixner, 

 Director of the Agricultural Experiment Station at Mockern, Germany. 



The percentage of digestible constituents in feeding stuffs is calcu- 

 lated from the difference between the constituents of the food and the 

 feces, it being assumed that the feces consist principally of the residue 

 of the food. In determining the digestible nutrients of a feeding- 

 stuff it is necessary to determine both the amount and the composition 

 of the food and the feces. In regard to the latter, it is essential that 

 the feces represent the feeding stuff under experiment, not only quali- 

 tatively but also quantitatively. Accordingly in the case of herbiv- 

 orous animals, considering their extensive and complicated digestive 

 tract, it is necessary to insure the complete removal of all residues in 

 the digestive apparatus from the previous feeding before the feces for 

 the investigation are quantitatively collected. Furthermore, as the 

 voiding of feces is very irregular from day to day and the amount may 

 differ by more than 30 per cent, the feces must be collected without 

 loss for a considerable time. 



DURATION OF THE EXPERIMENT. 



A digestion experiment is divided into a preliminary period, in which 

 the residues from previous feeding are excreted from the body; and a 

 feeding period proper, during which the feces must be quantitatively 

 collected. On the basis of numerous investigations it is safe to con- 

 clude that the preparatory feeding should last at least 5 days in the 

 case of ruminants, and 3 or 4 days in the case of horses and pigs. It 

 is safer, however, to continue the preparatory feeding for 8 days with 

 ruminants and for G days with horses and pigs. Under certain excep- 

 tional conditions, when a very easily digestible feeding stuff is to be 

 tested and foods which are difficult to digest have been previously fed, 

 the preparatory period should be even longer. In such cases the micro- 

 scope may be used with advantage in examining the feces for traces of 

 the previous food. The main period, in which the feces are quantita- 

 tively collected, should last at least 8 to 10 days with ruminants and 6 

 days with other animals. 



SAMPLING THE FEEDING- STUFFS. 



Throughout the experiment, including the preparatory period, there 

 should be no variation in the composition of the rations. In the case 

 504 



