PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 79 



requirements for milk production are much lower tlian the current feed- 

 ing standards would indicate, the experiments of Haecker(^^), Hills and 

 associates (^*), Ellett, Holdaway, and Harris (^^), Fries, Braman, and 

 Kriss(®^), Perkins(*), and particularly Buschmann(^) indicate that 

 little if any increase in milk production may result from increasing the 

 protein intake above the minimum requirements. Seven's (^') self- 

 feeding experiments on dairy cows also offer no support — in fact quite 

 the contrary — for the belief that nitrogenous concentrates are stimu- 

 lants to the mammary glands/ It is probably still premature to deduce 

 any final conclusions on this point, since there is great need for a careful 

 definition of " minimum " and " optimum " and for crucial, carefully 

 planned and carefully controlled investigations concerned specifically 

 with this question. It is equally true, however, that the theory of opti- 

 mum protein nutrition, exceeding the minimum, is difficult to explain on 

 physiological grounds, and has suffered rather than benefited by the 

 later experimental work in milk production. 



BIBLIOGRAPHY 



1 Mitchell, H. H. The determination of the protein requirements of animals and 



of the protein values of farm feeds and rations. Bull. Nat. Res. Counc, 

 No. 55, 44 p. (1926). 



2 Armsby, H. P. The nutrition of farm animals. New York. P. 326-330 (1917). 



3 Sherman, H. C. Protein requirement of maintenance in man and the nutritive 



efficiency of bread protein. J. Biol. Chem., 41: 97-109 (1920). 



4 Perkins, A. E. Protein requirement of dairy cows. Ohio Agr. Exp. Sta. Bull., 



389, 35 p. 



5 Buschmann, A. Untersuchungen liber den Eiweissbedarf der Milchkuh und den 



Einfluss eiweissreicher und Eiweissarmer Fiitterung auf die Menge und 



Zusammensetzung der Milch. Landw. Vers.-Sta., 101: 1-216 (1923). 

 ^Hindhede, M. Adequate protein minimum in dietaries. Ugeskrift for Laeger, 



79: nos. 13, 14 and 15. Abstracted in Chem. Abst., 11: 2344 (1917). 

 ''Forbes, E. B., Fries, J. A., and Kriss, M. The maintenance requirement of cattle 



for protein as indicated by the fasting katabolism of drj' cows. J. Dairy 



Sci., 9: 15-27 (1926). 



* Such negative evidence as that cited may, in a certain sense, be of more 

 significance than the positive evidence obtained in earlier investigations not 

 specifically referred to. When positive indications of a stimulating effect of excess 

 protein are obtained in practical feeding tests, it is, in fact, difficult if not impossible 

 to prove from the data obtained that the increase in milk production was catised 

 by the increase in protein consumed, since other variable factors have operated. 

 On the other hand, when large increases in protein intake above the apparent 

 requirements fail to cause an increase in milk production, such evidence is directly 

 contradictory to the theory of protein stimulation, except on the assumption that 

 there are counteracting factors at work. This complicating assumption is obviously 

 not the most rational nor the simplest interpretation of the data. 



