520 Report of the Department of Animal Husbandry of the 



as our results indicate, in providing raw material for the secre- 

 tion of milk fat or milk sugar, a large part of this generous pro- 

 tein supply is not needed for constructive purposes. 



When fed what is sometimes called the Grerman balanced ra- 

 tion, a cow may sometimes yield thirty pounds of average milk, 

 generally less rather than more. This milk would contain not 

 over one pound of protein, leaving one and a half pounds or three- 

 fifths of that in the ration unused, so far as known, for any neces- 

 sary constructive purpose. We desire to propose as a rational 

 explanation of the notable influence upon milk secretion of an 

 abundant supply of digestible protein in the ration, that it is due 

 to the influence of protein upon metabolic activity rather than 

 because so much was needed from which to form milk solids. 

 This view would not minimize our estimate of the importance of 

 the nitrogenous constituents of cattle foods, but simply empha- 

 sizes more fully one reason, and perhaps the main one, why they 

 should be supplied in such generous proportions. 



Certain data from this experiment should be considered in this 

 connection. 



It appears that the daily digestible protein in the ration varied 

 in the different periods between 1.85 lbs. as a maximum to 0.41 as 

 a minimum. There was a corresponding, though not so vdde, va- 

 riation in the urea nitrogen, and it is interesting to note the rela- 

 tion between the protein supply, protein metabolism and the 

 secretion of milk solids, as shown both by the figures and by the 

 diagram. 



Relation Bktween Protein Supply, Protein Metabolism and Secretion 



OF Milk Solids. 



Digestil)le pro- 

 tein eaten daily. 



Lbs. 



.70 

 .42 

 .85 

 .90 

 41 

 58 



Protein equiva- 

 lent of urine 

 nitrogen ex- 

 creted daily. 



Lbs. 



1.03 

 .74 

 .86 

 .46 

 .40 

 .61 



Gain or loss of 

 body protein 

 daily. 



Lbs. 

 + 03 

 -f.06 

 +.41 

 —.05 

 —.44 

 +.45 



Milk solids 

 secreted daily. 



Lbs. 

 2.72 

 2.28 

 2.22 

 1.87 

 1.67 

 1.96 



Relation of pro- 

 tein destruc- 

 tion to milk 

 solids secreted. 



100:2.64 

 100: 3.02 

 100:2.59 

 100:4.06 

 100:4.19 

 100:3.21 



