Mar. 25, 1915 Energy Values of Feeding Stuffs for Cattle 449 



results for the two quantities being as shown in Table V. On the other 

 hand, upon the heavy hay ration and also upon the mixed ration of hay 

 and grain steer C was distinctly inferior to steer E, losing more chemical 

 energy in both methane and feces. This was the most distinct individual 

 difference in these experiments. It should perhaps be noted that steer C 

 showed a tendency to bloat and to get off feed on heavy rations and possi- 

 bly did not have full normal digestive power. In experiment 211 steer D, 

 then a year older, on the average of three periods on mixed hay again 

 showed a slight inferiority to another animal which presumably had 

 received better feeding during growth. 



Clearly individual differences between the animals had no very mate- 

 rial influence on the losses of chemical energy in these experiments. 

 In most instances the differences are well within the limits of error for 

 such determinations, and even in those cases where there seem to be 

 distinct individual differences they are comparatively slight, being of 

 about the same magnitude as those observed by G. Kiihn (28) and 

 rather smaller than those found by Armsby (i) in experiments on three 

 steers. 



VARIABILITY OF METABOLIZABLE ENERGY 



The results recorded in Tables III and IV show clearly that the metab- 

 olizable energy of a feeding stuff is by no means a constant. Not 

 only do the averages for feeding stuffs of the same name differ more or 

 less, but the raetabolizable energy of the same sample is more or less 

 variable in the different periods. 



The losses of chemical energy which a feeding stuff suffers are sub- 

 stantially determined by the nature and extent of the digestive pro- 

 cesses. Digestibility, however, especially in ruminants, is a very com- 

 plex affair, depending on many factors. Broadly speaking, it may be 

 characterized as a series of fermentations, effected in part by a variety 

 of organized ferments and in part by enzyms secreted by the digestive 

 organs or contained in the feed itself. Changes in the composition of 

 the contents of the digestive tract or in the rapidity with which they 

 move forward through it can hardly fail to influence in a ^'ariety of 

 ways the course of these fermentations, and it seems on the whole rather 

 surprising that they go forward as uniformly as they do. 



In these experiments they appear to have been affected chiefly by 

 the variations in the amount of feed consumed. Recently Zuntz and 

 his associates (20, 53) have reported striking instances in which the 

 extent of the methane fermentation in particular has been markedly 

 affected by the make-up of the rations and especially by the order in 

 which the feeds were consumed, while Voltz and his associates (47, 48) 

 have laid much stress on the practical importance of these results. 

 No such marked differences occurred in our experiments, but, on the 

 other hand, the range of feeds was not so wide. It is perhaps too early 



