158 SCIENCE AND PRACTICE OF CHEESE-MAKING 



horns prevail. The foregoing table represents aver- 

 ages in the case of three to six individuals of each 

 of seven different breeds for an aggregate of four 

 to twenty lactation periods with each. 



Influence of stage of lactation on fat content of 

 milk. From the time a cow "comes fresh in milk" 

 up to the time she becomes "dry," the composition 

 of the milk undergoes gradual changes, which are 

 quite independent of other factors. The period of 

 lactation varies in length with different individual 

 cows, but, for practical purposes, lasts about 10 to 

 12 months. The changes observed in the percent- 

 age of fat during the progress of the lactation 

 period are quite marked and fairly regular, with- 

 out reference to individual or breed. The colos- 

 trum, which is the secretion produced by a cow 

 soon after calving, is very different in composition 

 from normal milk and is not considered at all in 

 our discussion of the constituents of milk, because 

 it has no interest for us in this connection. The 



VARIATION OF PERCENTAGE OF FAT IN MILK WITH 

 ADVANCE OF LACTATION 



