16 MARKET DAIRYING 



milk from the same cow may vary a great deal in compo- 

 sition. The causes of these variations may be assigned 

 to two sets of conditions : I. — Those natural to the cow. 

 II. — Those of an artificial nature. 



I. QUALITY OF MILK AS AFFECTED BY NATURAL CONDI- 

 TIONS. 



1. The composition of the milk of all cows undergoes 

 a change with the advance of the period of lactation. 

 During the first five months the composition remains prac- 

 tically the same. After this, however, the milk becomes 

 gradually richer until the cow "dries up." The following 

 figures from Van Slyke illustrate this change: 



Month of Per cent of fat 



lactation. in milk. 



I ._ 4-54 



2 ; 4-33 



3 4-28 



4 4-39 



5 4-38 



6 4-S3 



7 4-56 



8 4-66 



9 4-79 



10 S.oo 



It will be noticed from these figures that the milk 

 actually decreases somewhat in richness during the first 

 three months of the period. But just before the cow dries 

 up, it may test as high as 8%. 



2. The quality of milk also differs with different 

 breeds. Yet breed differences are less marked than those 

 of the individual cows of any particular breed. 



Some breeds produce rich milk, others relatively poor 



