74 



MAINTENANCE RATIONS OF FARM ANIMALS. 



THE PROTEIN REQUIREMENT FOR MAINTENANCE. 



PROTEIN KATABOLIZED DURING EASTING. 1 



It has already been shown on pages 11-12 that in the previously 

 well-nourished fasting animal the katabolism of protein supplies 

 but a small part of the total energy required for the support of the 

 vital functions. As a preliminary to the consideration of the protein 

 requirement, however, some further consideration of the protein 

 katabolism during fasting is desirable. 



INFLUENCE OF PREVIOUS FEED. 



The classic experiments of Carl Voit upon fasting dogs showed 

 that while the protein katabolism in the early da} T s of fasting may 

 vary widely according to the previous feed, it soon falls to a com- 

 paratively low level which is approximately the same for the indi- 

 vidual animal whatever its amount upon the initial days. This 

 behavior is well illustrated by the following results, all upon the 

 same animal, which have been fully confirmed by numerous subse- 

 quent experiments. 2 



Protein katabolism of fasting dog — Voit. 





2,500 grams 

 meat. 



1,800 grams 

 meat; 250 

 grams fat. 



1,500 grams 

 meat. 



1,500 grams 

 meat. 



Bread. 



Urinary nitrogen 3 per day: 



Last day of feeding 



First day of fasting 



Second day of fasting 



Third day of fasting 



Fourth day of fasting 



Fifth day of fasting 



Sixth day of fasting 



Seventh day of fasting 



Grams. 

 84.4 

 28.1 

 11.6 

 8.9 

 8.1 

 5.7 

 6.2 

 5.8 

 4.7 



Grams. 

 60.7 

 17.5 

 10.9 

 7.8 

 6.9 

 5.9 

 6.0 

 5.6 



Grams. 

 51.7 

 13.9 

 8.5 

 8.2 

 7.0 

 6.6 

 6.1 

 5.6 

 6.0 



Grams. 

 51.7 

 12.4 

 8.7 

 7.3 

 7.0 

 6.9 

 6.0 

 6.0 

 5.6 

 5.6 

 5.3 



Grams. 

 11.5 

 9.1 

 7.3 

 7.0 

 6.2 

 5.9 

 6.1 



Eighth day of fasting 



Ninth day of fasting 









Tenth day of fasting 













i 







FASTING KATABOLISM VARIABLE. 



It is not true, however, as is sometimes loosely stated, that the 

 protein katabolism of a fasting animal is a constant quantity. On 

 the contrary, in the presence of an adequate amount of body fat, its 

 amount tends to diminish with the progress of fasting. This fact 

 appears more or less clearly in the foregoing experiments, while in 

 later ones it is quite marked. For example, in the experiments by 



1 Compare references on p. 8. 

 2 Zeitschrift fur Biologie, vol. 2, p. 307. 



3 Computed from Voit's figures for urea. In earlier experiments upon the protein 

 metabolism the urea in the urine, as determined by Liebig's titration method, was com- 

 monly taken as the measure of protein katabolism. Later experience has shown that 

 these results are not strictly accurate, but the amount of urea under such circumstances 

 is so nearly proportional to the total urinary nitrogen that the results as given above are 

 entirely adequate as an illustration of the point under discussion. 



