664 NUTRITION OF FARM ANIMALS 



marked effect of maize in noticeably increasing the metabolism, 

 especially during standing. This result is of interest in view 

 of Zuntz and Hagemann's observations on the stimulating 

 effect of maize upon the metabolism of the horse, which were 

 also made on the standing animal, although no increase in the 

 minor muscular activity was reported. Grain mixture No. i, 

 containing 43 per cent of maize meal, likewise showed a similar 

 effect, although with grain mixture No. 2, containing 60 per 

 cent of maize, it was much less marked, possibly on account 

 of the lower content of protein (12.5 as compared with 17.5 

 per cent). 



764. Influence of amount of feed consumed. In the dis- 

 cussions of the foregoing paragraphs it has been tacitly as- 

 sumed that both the losses of chemical energy in the excreta 

 and the increment of heat production consequent upon feed 

 consumption are proportional to the quantity of feed ingested, 

 i.e., that the net energy values per unit of feed are substantially 

 unaffected by the amount consumed or by the plane of nu- 

 trition of the animal. 



This seems not to accord with the general belief that heavy 

 rations are relatively less effective than lighter ones and that 

 the fat animal utilizes its feed less efficiently than the thin 

 one. It became clear, however, in the course of the study, in 

 Part III, of the feed requirements for various forms of pro- 

 duction, that a variety of factors are influential in determining 

 the actual outcome of feeding operations and that diminishing 

 returns from heavy or long continued feeding do not neces- 

 sarily imply a diminishing efficiency of the feed as a source of 

 body material or energy. On the other hand, however, sur- 

 prisingly little specific investigation appears to have been de- 

 voted to this fundamental question. 



Obviously, differences in the amount consumed might influ- 

 ence the net energy value of a feeding stuff either by affecting 

 the extent to which chemical energy is lost in the excreta (i.e., 

 the metabolizable energy) or by affecting the magnitude of the 

 losses due to increased heat production. 



Influence on metabolizable energy. That in mixed rations the 

 digestibility may suffer more or less on heavy feeding has already 

 been shown in Chapter XVI (722), notably in Eckles' and Armsby and 



