THE PRODUCTION VALUES OF FEEDING STUFFS 663 



and woody feeding stuffs, like hay, straw, stover, etc., as re- 

 quiring a greater expenditure of energy in their digestion and 

 assimilation than the more concentrated and highly digestible 

 grains, for example. It may be somewhat surprising, there- 

 fore, to note the relatively small differences in this respect be- 

 tween different classes of feeding stuffs, as well as the fact that, 

 in case of cattle, the average is distinctly higher for the con- 

 centrates than for the roughages, viz., 58.75 Therms per 100 

 pounds dry matter as compared with 46.54. While the me- 

 chanical work required for the digestion of concentrates is pre- 

 sumably less than that necessary in case of roughages on ac- 

 count of the greater expenditure for the mastication of the 

 latter, this difference appears to be more than compensated for 

 by other factors, so that on the whole fully as great an incre- 

 ment of the heat production results from the consumption of 

 the concentrates. As a class, concentrates are superior to 

 roughage, not because their consumption involves a less ex- 

 penditure of energy but because they contain more metaboliz- 

 able energy, so that more remains available for body use after 

 the expenditure has been met. 



763. Differences between feeding stuffs. But while the 

 foregoing results do not show the existence of the great contrast 

 between the two chief classes of feeding stuffs in their effects 

 on the energy expenditure of the body which seems at times to 

 have been assumed, they nevertheless reveal distinct differences 

 even between feeding stuffs of the same class. Thus, among the 

 hays a distinct increase is found from timothy hay with an 

 average heat increment of 35.47 Therms through mixed hay 

 and clover hay up to alfalfa, with an average of 53.03 Therms. 

 Apparently the legumes cause a distinctly greater increase in 

 the metabolism than do the grasses. The chief difference be- 

 tween the two seems to lie either in their effect upon the work 

 of peristalsis or in the degree to which they stimulate the general 

 metabolism. One can hardly doubt that the latter is the 

 chief cause and is naturally inclined to associate it with the 

 higher percentage of protein in the legumes. That other causes 

 may also be operative, however, is indicated by the result on 

 maize stover, which is nearly as high as in the case of alfalfa 

 and shows a similar distribution among the several factors. 



Among the concentrates there may be noted in particular the 



