320 NUTRITION OF FARM ANIMALS 



according to the amount of protein supplied in the feed, while 

 for each level of protein stock a certain supply in the feed is 

 necessary that is, the protein requirement for maintenance 

 varies. With carnivora on a largely protein diet the adjust- 

 ment, of the body to the protein supply seems to take place 

 rather promptly. In the case of herbivora, however, the ad- 

 justment appears to be more gradual, possibly owing to the 

 relatively large supply of non-nitrogenous ingredients in their 

 feed, and apparently some gain of protein may continue for a 

 considerable time, although when expressed as a percentage of 

 either the total feed protein or of the body protein the gain is 

 relatively small. 



407. Effect of deficiency of non-nitrogenous nutrients. 

 The prime demand of the organism is for energy for the per- 

 formance of its vital functions, and if necessary it will draw 

 upon its own tissues for this purpose. No clear conception of 

 the laws of protein metabolism can be reached without taking 

 into consideration the energy relations. 



As has already been shown, the proteins or at least the cleavage 

 products of their digestion readily undergo a process of deam- 

 inization by which their nitrogen is split off and excreted, leaving 

 a non-nitrogenous residue which is available as a source of 

 energy. Ordinarily, however, the proportion of energy derived 

 from the katabolism of protein is relatively small, the non- 

 nitrogenous nutrients constituting its principal source. 



But if, with an amount of protein in the feed just sufficient 

 to sustain nitrogen equilibrium, the non-nitrogenous nutrients, 

 especially the carbohydrates, be so reduced in amount that 

 the total energy supply is insufficient for maintenance, not 

 only is body fat drawn upon to make up the deficit, but the 

 protein katabolism also increases, so that a supply of this 

 nutrient which was previously adequate became insufficient 

 and a loss of body protein occurs. 



The effect is naturally most marked when the non-nitrogenous 

 nutrients are withdrawn altogether. For example, Voit and Korku- 

 noff 1 found that when a dog was given an abundant supply of carbohy- 

 drates, protein equivalent to about 4.5 grams of nitrogen was sufficient 

 to maintain him in nitrogen equilibrium. But when a similar amount 



1 Ztschr. Biol., 32 (1895), 67. 



