MILK 



15 



milk changes decidedly in composition. The percentage of protein and fat rises 

 rapidly. The total protein may be one-third higher than at the middle of the 

 lactation period but the proportion of casein and albumin remains unchanged. 

 The butterfat changes decidedly both as to the size of the globules and chemic- 

 ally. Toward the end of the lactation period the cream becomes difficult and 

 even impossible to churn. The milk of some of the cows develops an abnormal 

 flavor and odor." 



Seasonal Variation in Composition. Not only does the character 

 of milk change with the advance of the lactation period but, as Richmond 

 has shown, it exhibits a distinct seasonal variation in quality. The year 

 can be divided roughly into four periods thus: 



1. November, December, and January; the milk is rich in fat and 

 solids-not-fat. 



2. February, March and April; the solids do not show appreciable 

 diminution but the fat becomes less in quality. 



3. May, June, July and August; the fat is low though there is a tend- 

 ency for it to rise at the end of the period. In July and August the 

 solids-not-fat are below average. 



4. September and October; an improvement in quality both in fat 

 and in solids-not-fat occurs. 



Breed of Cow and Production of Butterfat. That the breed of cows 

 influences both the quality and quantity of milk produced has long been 

 known. Table 9, compiled from the analyses of Lythgoe of the Massa- 

 chusetts State Board of Health, those of the New York and of the New 

 Jersey Agricultural Experiment Stations, gives an idea of how breed 

 affects the quality of milk. 



TABLE 9. AVERAGE COMPOSITION OF THE MILK OF SEVERAL BREEDS OF CATTLE 



1 Casein. 



It is apparent that the breed of cattle has an important relation to 

 milk quality. The total solids which in a general way represent availa- 



