98 



MAINTENANCE RATIONS OF FARM ANIMALS. 



least amount of protein which may be used than as to the most ad- 

 vantageous level of protein nutrition; that is, as to the optimum of 

 protein. 



This question has been warmly debated in connection with human 

 nutrition. 



Numerous recent investigations, notably those by Chittenden and his asso- 

 ciates, 1 have shown that the protein of human dietaries can be reduced much 

 below the amount previously regarded as necessary. In most cases there is no 

 possibility of a direct comparison with the fasting katabolism of the same indi- 

 vidual, but as previously stated (p. 77) a considerable number of instances are 

 on record in which the nitrogen supply has been reduced to an amount mate- 

 rially lower than that usually found for the fasting protein katabolism of 

 individuals of the same weight without leading to a loss of protein from the 

 body. In all these experiments, the nonnitrogenous nutrients consisted, as is 

 usually the case in human dietaries, to a considerable extent of carbohydrates. 



Moreover, while some of the earlier experiments were for short periods and 

 on comparatively few individuals, Chittenden's investigations covered long 

 periods and were made on 26 different individuals, including 5 professional men 

 under observation for 8 months, 13 soldiers observed for 6 months, 

 and 8 trained athletes under observation for 5 months. His results clearly 

 demonstrate the possibility of maintaining the body protein and fully preserv- 

 ing the health and vigor upon a low protein diet. In other words, a relatively 

 low level of protein nutrition for several months is not inconsistent with health 

 and efficiency. 



In some of the earlier experiments in which very low protein diets were fed 

 to dogs, the health of the animals suffered seriously and there has been a 

 tendency to ascribe these ill effects to the continued use of very small amounts 

 of protein. Later investigations by Chittenden, however, in which dogs were 

 kept on a low protein diet for the greater part of a year, seem to have demon- 

 strated that the ill effects observed in the earlier experiments were due to un- 

 hygienic conditions and not to the low protein diet. It may be remarked that in 

 experiments upon cattle, rations very low in protein have been fed for a con- 

 siderable time without any perceptible deleterious effects. No similar determi- 

 nations upon other species of farm animals appear to have been made. 



On the whole, then, it can not be said that a considerable surplus of 

 protein over the minimum requirement for maintenance — that is, the 

 maintenance of protein nutrition on a high plane — has been proved 

 to be of any material advantage in the maintenance either of men or 

 domestic animals during periods covering several months. Whether 

 a continued low protein diet through years or generations would 

 show a different result is at present largely a matter of speculation. 

 It is to be remarked, however, that the particular point under dis- 

 cussion is the protein requirement of the mature organism. That a 

 deficiency of protein in the diet of a growing animal may have 

 disastrous results is clear. If, however, the habitual food supply 

 of a race of men or a group of animals is low in protein, the young 

 are likely to share this deficiency with the mature, and it seems not 



1 Physiological Economy in Nutrition. Stokes Co., 1907. 



