THE PRODUCTION VALUES OF FEEDING STUFFS 667 



available, although it appears probable that they are higher 

 than the corresponding values for tissue production. A tenta- 

 tive method of utilizing the present net energy values in com- 

 puting the requirements of dairy cows was there proposed (605), 

 but definite experimental data are much to be desired. 



3. THE COMPUTATION OF NET ENERGY VALUES 



767. Importance. It is apparent from the foregoing para- 

 graphs that the number of actual experimental determinations 

 of net energy values as yet recorded is comparatively small 

 and that it can hardly be increased very rapidly, while it is 

 obviously impracticable to apply the laborious method of res- 

 piration and calorimeter experiments to all the great number 

 of feeding stuffs now in use. Determinations of the metabo- 

 lizable energy, in which at least the energy of the feeding stuffs 

 and of the visible excreta has been determined, are rather more 

 numerous, while there are on record the results of a great num- 

 ber of digestion experiments in which no determinations of 

 energy were made. It is highly important that the mass of 

 statistical data thus accumulated, and summarized in tables of 

 the composition and digestibility of feeding stuffs, should not 

 be incontinently thrown overboard simply because a newer 

 point of view has revealed more clearly its deficiencies. On the 

 contrary, it should be utilized to the fullest extent possible, in 

 connection with the as yet rather meager results of the more 

 recent experimental methods, for computing the net energy 

 values of such feeding stuffs as have not yet been subjected 

 to direct investigation. 



Computation from digestible nutrients 



768. Kellner's investigations. To Kellner is due the first 

 attempt to make practical application of the conception of the 

 feed as the source of energy to the body. In 1880, in his in- 

 vestigations upon the relations between muscular activity and 

 metabolism in the horse (637) he determined the additional 

 amount of work which the animal was able to perform as a 

 result of the addition to his rations of starch and of fat. He 

 expressed his results in terms of the percentage of the energy 



