GENERAL CHEMISTRY OF MILK 107 



It can be seen here that the fat leads in variability, that the 

 protein and total solids vary, and that the sugar and ash are the 

 least variable. 



Van Slyke and Publow give the following compositions of 

 milk from different breeds of cows: 



PERCENTAGE OF FAT AND CASEIN IN MILK FROM DIFFERENT BREEDS 



Per cent. Per cent. Relation 9f 



Breed. fat. casein. fat to casein. 



Holstein-Friesian 3.26 2.20 1:0.67 



Ayrshire 3.76 2.46 1:0.65 



American Holderness 4.01 2.63 1:0.66 



Shorthorn 4.28 2.79 1:0.65 



Devon 4.89 3.10 1:0.63 



Guernsey 5.38 2.91 1:0.54 



5.78 3.03 1:0.52 



These figures show clearly that with increased fat content the 

 amount of protein also increases, although not in the same ratio. 

 The fat increases at a greater ratio than the protein. 



A careful and exhaustive study of the differences in the com- 

 position of milk from four important breeds was made by Eckles 

 and Shaw. The authors examined samples of milk in four-week 

 periods throughout the lactation period, thus eliminating one 

 source of error resulting from the variation of fat during this period. 

 The results are shown in the following table: 



THE COMPOSITION OF MILK FROM DIFFERENT BREEDS OF COWS 



Shorthorn 12.09 3.73 3.38 2.74 4.99 282 26.28 34.36 227.6 33.23 



The work of Eckles and Shaw brings out the following impor- 

 tant facts in regard to the variability of milk constituents from the 

 breeds examined : 



Fat: The fat represents 28 to 35 per cent, of the total solids, 

 and varies within these limits according to breed. While in Jer- 

 sey and Guernsey milk an average of 34.9 per cent, of the solids 

 is fat, it is but 28.1 per cent, in Holstein milk. According to 

 Eckles and Shaw there seems to be no appreciable difference in 

 the nature of the fat of different breeds, except in the size of the 

 globules. In Jersey and Shorthorn milk large globules are pre- 

 dominant, while in Ayrshire and Holstein milk there are chiefly 

 small globules. The relation of the size of globules is given in 

 the following figures: Jersey milk, 328; Shorthorn milk, 282; 

 Ayrshire, 150; Holstein, 142. This relation is graphically illus- 

 trated in circles in Fig. 25. 



