620 NyTRITION OF FARM ANIMALS 



proximately 25 grams, so that apparently 25 grams less of pro- 

 tein is digested from the basal ration, while in reality the true 

 digestion may not have been affected. Thus in Kiihn's exper- 

 iment with hay and starch (723) the nitrogenous excretory 

 products corresponding to the 1646 grams dry matter of the 

 2 kgs. of starch consumed, would be approximately 40 grams, 

 while the excess actually found was 44 grams, the difference 

 being insignificant. 



The agreement is by no means always so close as in this 

 instance and in none of the experiments on the addition of car- 

 bohydrates which have been cited was the true digestibility 

 (166) of the protein determined. Nevertheless, the general 

 conclusion seems justified that at least the larger part of the 

 influence of carbohydrates and of feeding stuffs rich in car- 

 bohydrates on the apparent digestibility of the protein of the 

 feed is due to the fact that, when added to a basal ration, they 

 increase the nitrogenous excretory products in the feces. On 

 the other hand, however, it must be remembered, that while 

 the true digestibility may not be lowered, it is, as already 

 pointed out (167), the apparent digestibility which measures 

 the real advantage derived by the animal from the digestion 

 of its feed. Whether the increased excretion of nitrogenous 

 matter in the feces after carbohydrate feeding be due to an 

 apparent or a real depression of digestibility, or to both com- 

 bined, it is none the less a loss of protein from the body. 



In general the depression in the percentage digestibility of 

 the protein is greater the poorer the basal ration is in this in- 

 gredient. As Kellner x has pointed out, however, this does 

 not justify the statement frequently made that the magnitude 

 of the depression is dependent upon the nutritive ratio of the 

 feed. The difference is purely a mathematical one. A de- 

 crease of the digestibility of the protein by 50 grams, for ex- 

 ample, is relatively very much greater in a basal ration of oat 

 straw, containing only 140 grams of apparently digestible crude 

 protein than in a basal ration of meadow hay containing 430 

 grams of digestible protein. 



The fact that the addition of protein tends to decrease the 

 apparent digestibility of the protein of a basal ration is also 

 readily explicable from this point of view. Pfeiffer's exper- 



1 Landw. Vers. Stat., 44 (1894), 344. 



