800 EXPERIMENT STATION RECORD. 



(liffiTcnce is ;ilt<)j,'('tluT too lar^'c to })e iiscribed to any cxiKTiinnitnl cinii- or to lie 

 aiTomiti'd for l>y tlic (lisrrepancioH in Homo of tlic results. 



"This (lifffrcncc may he reasonably aHcribtMl to the rchitivciy larji;L' cxpenditur*' of 

 ener<;y nerossary in the digestion and assimilation of the hay. Even upon a com- 

 paratively lijrht ration, this amount, in addition to the heat arising from the internal 

 work of the ])ody, appears to have been sufficient to maintain tlie Jiormal ])ody 

 temperature at the comparatively liigh stable temi)eratur(! ( 1S.2° C. ). Such being the 

 ca.se, when jnore hay was added the heat arising from its digestion and a.ssimilation 

 was in excess of the needs of the animal for heat and ln'came an excretnm, passing 

 off without l)eing of any (hrect service to the organism. 



" In other words, what one of us has elsewhere designated as tlie critical amount 



of f 1 must ))(• relatively small in the case of a nuiteriallike timothy hay, which 



requiri's a large amount of digestive work. In our experiment, even the smallest 

 amount of food seems to have been in excess of the critical amount; consequently, 

 when more food was added the additional heat resulting from its digestion and 

 assimilation could not be used indirectly and served simjjly to increase the heat pro- 

 duction, while only the remaining (53 piT cent of the metabolizable energy served as 

 fuel for the body in place of the tissue ])reviously consumed." 



On tiie basis of theoretical considerations, which are discussed, the authors believe 

 that for cattle a maintenance ration is " a question of tissue replacement rather than 

 of heat production, and, therefore, that the value of a given feeding stuff for main- 

 tenance depends upon the availability of its energy. We may, for instance, regard 

 it as at least very probable that the work of digestion and assimilation in the case of 

 a material like corn meal would be materially less than in the case of hay; or, in 

 other words, that a larger percentage of its energy would be available for the main-' 

 tenance of ti.ssue. It would follow from this that in ease of a ration consisting 

 largely of grain a less amount of material or of metabolizable energy would l)e 

 reipiired for maintenance than in the case of a ration consisting exclusively of coarse 

 fodder. In other words, the maintenance ration is a variable rather than a constant, 

 depending upon the kind of food used." In the experiments reported the main- 

 tenance requirement of the steer, as computed, was 10,710 calories, the average 

 w^eight of the animal during the experiment being approximately 410 kg. 



"Computing to 500 kg. live weight, on the assumption tliat the maintenance 

 requirement is proportional to the two-thirds power of the live weight, this etjuals 

 12,197 calories. . . . 



"If the heat production upon the maintenance ration is in excess of the require- 

 ments of the animal, it seems unlikely that small variations in the stable tempera- 

 ture to wliich the animal is exposed will have the effect ni)on the maintenance 

 requirement which is ordinarily attributed to them. Still less is tliis likely to be the 

 case with fattening cattle, where the amount of food and the consequent heat i)ro- 

 duction are largely in excess of the maintenance ration. 



"Our results indicate that the proportion of the metabolizable energy of the food 

 which was utilized, above the maintenance requirement, to produce gain was decid- 

 edly less than that used below the maintenance requirement to prevent loss of tissue. 

 In other words, they indicate that the conversion of digested and assimilated matter 

 into actual tissue (fat) requires a considerable expenditure of energy, amounting in 

 this case to al)out 47 per cent of the available energy or 30 per cent of the metabo- 

 lizable energy. This result is quite in accordance with wliat we shoukl anticipate. 

 The digested matter of tlie food of herbivora appears to be resorbed chiefly in the 

 form of carbohydrates and of organic acids. It seems altogether probable that a 

 much less i)rofound change is required to convert these resorbed products into forms 

 suited to maintain the energy metal)olism of the organism than is needed to convert 

 them into the form of permanent tissue, especially fat. At the same time it should 



