106 MILK 



to the amount of solids present; this is of special importance when 

 the milk is destined for infant feeding. Furthermore, the digesti- 

 bihty of milk depends in a measure upon its composition, and 

 finally butter and cheese makers are interested to know the quan- 

 tity of products obtainable from a given milk. Not only the 

 quantity but also the quahty of milk products is influenced by the 

 milk composition. 



By far the majority of available data on the variability in 

 the composition of milk refer to fat content. Relatively httle 

 attention has been given to other constituents of milk. Further- 

 more, samples for analysis have frequently been taken without 

 consideration of such important factors as the kind and amount 

 of food taken by the cow and the stage of lactation. There are, 

 however, some apparently rehable data at hand and these wiU 

 be discussed under the following heads : 



1. Difference in composition due to breed. 



2. Difference in composition due to individuahty. 



3. Difference in composition of milk from the same individual. 



4. Difference in composition during the lactation period. 



5. Difference in composition due to kind and quantity of food. 



6. Difference in composition due to weather conditions and 

 temperature. 



7. Difference in composition due to exercise and other ner- 

 vous influences. 



8. Difference in composition due to the skill of the milker. 



9. Difference in composition due to the health of the animal. 

 10. Difference in composition due to dilution of milk. 



1. Difference in Composition Due to Breed. — It has been known 

 for some time that reported analyses of milk from various coun- 

 tries show differences. Whether these are due in part to climatic 

 conditions is not determined, but the theory has sometimes been 

 advanced that the percentage of fat is lower in warm climates 

 than in cold ones, since animals do not require as much heat 

 energy in southern regions. However this may be, it is certain 

 that the breeds which are most prevalent are responsible for marked 

 differences in milk composition in various countries. That breeds 

 differ widely in the composition of the milk they yield is shown by 

 the following table taken from Swithinbank and Newman: 



THE COMPOSITION OF MILK FROM SOME BREEDS OF COWS 



Breed. 



American Grade Shorthorn 



Ayrshire 



Devon 



Guernsey 



Holstein 



Jersey 



Shorthorn 



Brown Swiss 



