54 PROTEIN REQUIREMENTS OF CATTLE: MITCHELL 



ferent breeds. Again, Andersen and Langmack(^^) in 1923 published 

 the results of a study of 1080 analyses of the milk of Eed Danish cows, 

 from which they derived the equation p = 1.597 + 0.446 f. From his 

 study of the 543 analyses of milk published by Haecker, Gaines (^") 

 arrived at the equation p = 1.46 + 0.40 f. 



These proposed formulas are not satisfactorily concordant. It is par- 

 ticularly significant that Haecker's data on the composition of milk, 

 upon which the Haecker, Savage, Eckles, and Armsby feeding stand- 

 ards for milk production are directly or indirectly based, indicate a much 

 lower protein content for milk of any grade than any of the formulae 

 derived from other sets of analyses. This discrepancy is too large to be 

 accounted for by the use of a different protein factor applied to the total 

 nitrogen analyses. The factor used by Haecker is not reported in his 

 publication.^ 



Illinois investigations on the composition of cows' milk. — A splendid 

 opportunity to throw further much needed light on the question of the 

 relation of the protein to the fat content of cows' milk was afforded by 

 the courtesy of Dr. 0. E. Overman, of the Department of Dairy Hus- 

 bandry of the University of Illinois in permitting the use for this purpose 

 of about 2000 analyses (largely unpublished)* performed in his labora- 

 tory during the last six years upon samples of milk of known antecedents. 

 In this extensive work, 3-day composite samples of milk were analyzed 

 every 5 weeks from each of 133 cows in the University herds, through 1 

 to 3 complete lactation periods. Analyses were thus secured upon 1002 

 samples of milk from 67 Guernsey-Holstein cross-bred cows, 208 samples 

 from 14 pure bred Ayrshire cows, 268 samples from 19 pure bred Hol- 

 stein cows, 200 samples from 15 pure bred Jersey cows, and 321 samples 

 from 18 pure bred Guernsey cows. The results with reference to fat and 

 protein (Nx6.38) have been averaged in groups covering a range in fat 

 content of 0.5 per cent, with the results given in Table 28. 



The correlation between the fat and protein percentages in these series 

 of analyses is not as high as that noted above. Overman has obtained 

 correlation coefficients of 0.635 for the Guernsey-Holstein analyses, 

 0.727 for the Holstein analyses, 0.679 for the Guernsey analyses, 0.588 

 for the Ayrshire analyses, and 0.500 for the Jersey analyses. 



* Although samples of milk from 53 cows are represented in Haecker's analyses, 

 it is significant that about 39 per cent of the samples (210 in number) were from 

 17 per cent (9 in number) of the cows, while 57 per cent (309 samples) were taken 

 from 28 per cent (15 in number) of the cows. These relations were called to the 

 attention of the author by Dr. O. R. Overman. 



^ The data will be published in full, with a statistical analysis, as a bulletin from 

 the Illinois Agricultural Experiment Station. 



