446 Journal of Agricultural Research voiiii, no6 



and experiment 212, steer H, periods i and 3), two on clover hay (experi- 

 ment 179, steer I, periods i and 2, and experiment 186, steer I, periods 

 2a and 3a), and one on alfalfa meal (experiment 212, steer H, periods 2 

 and 4). In the remaining 28 cases there is one in which the difference 

 amounts to only 0.02 per cent and two in which it is 0.04 per cent. In 

 the remaining 25 it ranges from 0.12 to 0.78 per cent. This greater 

 relative loss in the urine on the lighter ration can not be attributed to 

 the presence of nitrogenous substances derived from an increased katab- 

 olism of body protein, since the energy of the urine has been at least 

 approximately corrected to nitrogen equihbrium (p. 440) . Since it is well 

 established that the urine of cattle contains a considerable quantity of 

 nonnitrogenous substances (2, p. 312-314, 320-322), it seems not impos- 

 sible that the more extensive fermentation on the hghter ration may 

 have resulted in an increase of these unknown constituents. 



LOSSES IN FECES 



The results regarding the losses of chemical energy in the feces are 

 by no means so uniform as in the case of the methane and of the urine. 

 In 22 out of 33 cases there is a distinctly smaller relative loss of energy 

 in the feces with the lighter ration — i. e., a greater apparent digestibility — 

 the difference in the percentages ranging from 0.28 to 8.45. In the 

 other third of the cases, however, the difference is in the opposite direc- 

 tion, ranging from 0.37 to 2.74, with the exception of one case of prac- 

 tical equality, so that it appears that other factors besides the extent 

 of the methane fermentation affected the percentage digestibility. Two 

 rather marked cases of a greater loss of energy in the feces on the lighter 

 ration are found in experiment 211, periods 4 and 5, with relatively very 

 small rations. Whether the relative loss in the feces increases or de- 

 creases with an increase of the ration seems to bear no relation to the 

 total quantity of feed consumed either per head or per 500 kg. of live 

 weight. The 10 instances in which a greater percentage loss in the 

 feces was observ^ed on the lighter of the two rations include, it is true, 

 the more extreme rations as regards the total quantity, but the averages 

 for the two groups are not widely different (4,376 and 3,952 gm. of dry 

 matter). 



PERCENTAGE OF FEED ENERGY METABOLIZABLE 



The bearing of the foregoing facts upon the percentage of the feed 

 energy which is metabolizable is obvious. Clearly the fermentation 

 which plays so large a role in the digestive processes of ruminants was 

 relatively more intense on the lighter rations, resulting in the breaking 

 down of a larger proportion of the carbohydrates and in a greater loss 

 of chemical energy in the methane, accompanied in most instances by 

 an increased loss in the urine also. On the other hand, however, the 

 organic acids resulting from the fermentation are resorbed and oxidized 

 in the body, and their energy, together with the heat evolved in the 

 fermentation, constitutes part of the metabolizable energy of the feed as 

 defined on page 439. Whether the proportion of the total energy of the 

 feed which is metabolizable be greater or less on the lighter ration will 

 depend, therefore, upon the nature of the additional carbohydrates fer- 

 mented. If the increased fermentation attacks the more insoluble 

 carbohydrates, which would otherwise escape digestion entirely and 



