46 



MANUAL OF MILK PRODUCTS 



are the average for the whole period of lactation. The percent- 

 ages of fat for the different ages are as follows : 



2-year-olds . 

 3-year-olds . 

 4-year-olds . 

 5-year-olds . 

 6-year-olds . 

 7-year-olds . 

 8-year-olds . 

 9-year-olds . 

 10-year-olds 

 11- and 12-year 



■olds 



"Official" Weekly 



Tests of Holstein- 



Friesian Cows 



Number of 

 Cows 



147 

 81 

 59 

 37 

 36 

 22 

 14 

 10 



Average 

 Per Cent Fat 



3.29 



3.31 



3.41 



3.42 



3.34 



3.25 



3.40^ 



3.37 j 



3.83 



3.57 



Observations on Cor- 

 nell University Herd 

 1891-8 



Number of 

 Cows 



25 

 25 

 18 

 12 

 8 

 5 



Average 

 Per Cent Fat 



3.71 

 3.71 



3.68 

 3.60 

 3.49 

 3.68 



Influence of stage of lactation on fat-content of milk (Van Slyke). 

 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 ten to twelve 

 months. The changes observed in the percentage of fat during 

 the progress of the lactation period are quite marked and 

 fairly regular, without reference to individual or breed. The 

 colostrum, 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. The figures presented in the following table repre- 

 sent the monthly averages of nearly 100 different lactation 

 periods : 



