NUTRITIVE VALUE OF FEEDING STUFFS 35 



The results show that the dry matter of the corn silage was found to be 

 62.9 per cent digestible, the protein 55.3 per cent, the fat 82.1 per cent; i.e., 

 the digestion coefficients for the different components in the feed were as 

 follows (leaving off fractions) : Dry matter, 63; protein, 55; fat, 82; fiber, 

 45; nitrogen-free extract, 72, and ash, 18. 



If the digestion coefficients for the organic matter in silage is wanted, 

 it is readily obtained by calculating the amount of this component in the 

 feed and feces, as follows: In silage, 20.55 (dry matter) minus 0.88 pound 

 (ash) equals 19.67 pounds (organic matter) ; in feces, 7.62 less 0.72 -equals 

 6.90; 19.67 less 6.90 equals 12.77; percentage digestible, 12.77 divided by 

 .1967 equals 64.4. It was found, therefore, that 64 per cent of the organic 

 matter of the silage was digestible. 



In the case of feeding stuffs that cannot be fed alone (i.e., a grain 

 feed for ruminants) it is necessary to feed it along with some feed 

 of known digestibility that will supplement it so that when fed 

 together they will make at least a fairly normal ration. The cal- 

 culated amounts of digestible components in the second feed are 

 then deducted from the total digestible amounts of the various 

 components in the ration fed, and the difference is calculated on a 

 percentage basis of the total amounts present in the feed whose 

 digestibility was to be determined (Fig. 8). 



Interpretation of Results. The figures obtained in digestion 

 trials show the proportions of the components of the feed that have 

 been dissolved by the digestive fluids of the body and retained for 

 the uses of the animal. This is true only in a general way, for 

 various factors render the matter much more complicated. There 

 reappears in the dung not only the undigested matter of the feed, 

 but small amounts of residues of the digestive juices, waste prod- 

 ucts in the activity of the digestive organs, .and intestinal mucus. 

 The amount of these waste products in the dung can, however, be de- 

 termined in the laboratory and a correction made accordingly. This 

 is done by means of artificial digestion of the dung with a pepsin- 

 hydrochloric-acid solution (Kiihn's method), and making proper 

 deductions for these in the calculations. Another and more serious 

 source of error is introduced by the fact that the feed is subjected 

 to the action of bacteria and ferments in the paunch and intestines 

 through which gaseous products are formed, as previously stated 

 (p. 30). These attack especially the fiber of plant materials, and 

 the figures obtained for the digestibility of these Components, there- 

 fore, include a portion which has not been dissolved by the digestive 

 fluids of the animals and taken into circulation. This portion 

 does not contribute to the maintenance or the growth of the body, 

 and is of value to the animal only in so far as the heat generated 

 by the fermentation processes helps to maintain an even body 

 temperature. In spite of these errors to which digestion trials 

 are subject, the result obtained by them are. of greatest value 

 to both the feeder and the student of nutrition problems. Until 



