RELATIVE VALUES OF FEEDING STUFFS 609 



Crude fiber appears to be relatively difficult of digestion by 

 fowls and the results obtained upon this ingredient were vari- 

 able and apparently capricious. Aside from this, a comparison 

 of results with those for swine shows quite a close general 

 agreement between the two classes of animals. 



718. Individuality. In addition to the specific differences 

 just considered, differences have likewise been observed in the 

 digestibility of the same feeding stuff by individuals of the 

 same species. To some extent this may be due to abnormal- 

 ities, such as defective teeth or chronic diseases of the digestive 

 organs, but in normal animals distinct individual differences 

 also seem to occur. 



In their compilation of the results of American digestion ex- 

 periments, Jordan and Hall x were unable to find conclusive 

 evidence of such differences in digestive power and are inclined 

 to attribute the apparent variations which were observed largely 

 to the variability at different times already considered (712). 

 The experiments by G. Kiihn, 2 however, which were cited in 

 the discussion of the latter possibility, seem also to afford in- 

 dubitable instances of individual differences in* cattle and the 

 same is true of experiments by the writer 3 in which three 

 grade Shorthorn steers were under observation at different times 

 for five years. Carmichael, Newlin and Grindley 4 have like- 

 wise observed significant differences in the digestive powers of 

 individual pigs. On the other hand, Christensen and Simpson 5 

 made three series of digestion trials on alfalfa hay for two suc- 

 cessive years, using four range steers each year, and failed to find 

 any consistent individual differences. 



The existence of time variations in digestibility (712) renders 

 it somewhat difficult to decide whether an observed difference 

 in the digestion of the same feeding stuff by two animals is really 

 an expression of individuality or whether it is in a sense acci- 

 dental. A comparison based on a single digestion trial as or- 

 dinarily made is liable to be misleading, and to secure correct 

 results requires either a number of trials or a trial extend- 

 ing over a longer period than is ordinarily employed. On the 



1 U. S. Dept. Agr., Office Expt. Stas., Bui. 77 (1900), 88. 



2 Landw. Vers. Stat., 29 (1883), 129, 147, 153. 

 8 Penna. Expt. Sta., Bui. 42 (1898), 124. 



4 Science, July 2, 1915, p. 38. 5 New Mexico Expt. Sta., Bui. 91 (1914). 



2 R 



