especially upon coarse feeds, Kellner* has shown the same thing 

 to be true in the fattening of cattle, the authorst have demonstrated 

 that it also holds in the case of maintenance and sub-maintenance 

 rations of cattle, and RubnerJ himself has shown that his earlier 

 results were due to the comparatively low temperatures at which 

 he experimented and constituted a special case of a general law. Opin- 

 ions are still more or less divided as to the cause of the phenomenon, 

 but there is no dispute as to the fact. Only a part of the metabol- 

 izable energy of the feed is ordinarily substituted for energy previ- 

 ously derived from the katabolism of protein and fat in the body or 

 is recovered in the gain of flesh and fat made by the animal on 

 abundant feeding. 



Method of Determining Availability. 



The relation between the amount of metabolizable energy 

 supplied to the animal in its feed and the resulting effect upon the 

 body may be determined by a comparison of two periods in which 

 different amounts of the feeding stuff or ration in question are con- 

 sumed. For example, in Periods III and IV of the experiments 

 of 1905, two different amounts of the same timothy hay were fed. 

 After making the necessary corrections as described in the detailed 

 account of the experiments to be published later, it was found that 

 the metabolizable energy of the rations consumed and the gain 

 of energy by one of the animals (a loss being regarded as a nega- 

 tive gain) were as follows : 



Metabolizable Energy Gain of Energy 



of Ration by Animal 



Period IV 5981.4 Cals. - 680.2 Cals. 



Period III 3641.4 Cals. 2096.1 Cals 



Difference 2340.0 Cals. 1415.9 Cals 



The excess of 2340 Cals. of metabolizable energy in Period IV 

 as compared with Period III reduced the loss of potential energy 

 from the body by only 1415.9 Cals. In other words, only 60.5 per 

 cent, of the additional metabolizable energy supplied in Period 

 IV was substituted for energy previously derived from the kata- 

 bolism of body substance, while the remainder was disposed of by 

 an increase of 924.1 Cals. in the heat production of the steer, cor- 



* Landw. Vers. Stat., 44, 257; 47, 275; 50, 245; 53, 1. 



t U. S. Dept. Agric.. Bureau of Animal Industry, Bulletins 51, 74 and 101; 

 mdw. Jahrb.,32, 665; 34, 861; 37, 423. 



Gesetz e des Enefgieverbrauchs bei der Ernahrung, 1902. 



(9) 



