THE PRODUCTION VALUES OF FEEDING STUFFS 641 



The 144 Cals. of energy contained in the fat, however, although 

 not actually transformed into other forms of energy, were capable of 

 such transformation had the demands of the organism required it, 

 and therefore constitute part of the metabolizable energy of the feed. 

 With the 380 Cals. contained in the protein stored up, however, the 

 case is different. Had these 66.6 grams been katabolized, part of 

 their energy would have escaped in the resulting nitrogeneous meta- 

 bolic products. According to Rubner each gram of urinary nitrogen 

 derived from lean meat is equivalent to 7.45 Cals. of chemical energy. 

 The katabolism of the 66.6 grams of protein, therefore, would have in- 

 creased the chemical energy of the urine by 83 Cals., while only 297 

 Cals. would have been transformed. This amount of 83 Cals. must 

 consequently be added as a correction to the urinary energy as measured 

 in computing the metabolizable energy. In case of a loss of protein 

 from the body a similar correction must evidently be subtracted. 



When a respiration apparatus for the determination of the 

 combustible gases is not available, their amount may be esti- 

 mated from the digestible carbohydrates in the manner al- 

 ready outlined (745) , so that it is possible to estimate the metab- 

 olizable energy with a considerable degree of accuracy from the 

 results of an ordinary digestion experiment to which has been 

 added the collection of the urine and determinations of the heats 

 of combustion of the visible excreta. The additional labor 

 thus required is so small that it is to be hoped that in future 

 digestion experiments it may be undertaken whenever possible 

 and that in this way more extensive data may be secured re- 

 garding the metabolizable energy of feeding stuffs. While 

 such results do not show the production values of the rations 

 (750), they constitute an important step toward their more 

 exact determination. 



749. Experimental Results. There are on record a some- 

 what limited number of experiments with cattle and a few 

 with swine in which the losses of energy in the feces, urine and 

 methane respectively have been determined directly, while in 

 a considerably larger number the losses of methane have been 

 estimated from the digestible carbohydrates (crude fiber plus 

 nitrogen-free extract) in the manner just described. The re- 

 sults of these experiments are recorded in Table iSS, 1 which 

 shows the percentages of the gross energy which were carried 



1 This table is not claimed to be an exhaustive compilation of data, but is be- 

 lieved to be fairly complete. 

 2 T 



