CHAPTER XXIII. 



FEEDING MILK COWS. 



Milk cows are fed for the purpose of producing milk or butter 

 fat. It was formerly believed that milk is extracted directly 

 from the blood of the cow. But casein and milk sugar, which are 

 constituents of the milk, cannot be extracted from blood, because 

 they are not present in blood. Apparently, milk is elaborated 

 from the blood and lymph by chemical changes within the cells of 

 the udder. 



Factors which Influence Milk Production. A number of fac- 

 tors influence the quantity and composition of the milk. 



Breeds of Animals. Milk cows are divided into two groups of 

 breeds, those giving relatively large quantities of milk with 

 moderate fat content, and those giving less milk with a higher 

 percentage of fat. To the first group belong the Holsteins, 

 Ayrshires, Durhams, etc., and to the second, the Jersey and 

 Guernsey. The average by Konig of about five hundred analyses 

 of milk from animals belonging to these two groups, is as follows : 



Individuality. Individuals of the same breed vary decidedly in 

 the quantity and composition of the milk they give. For example, 

 a study of each individual in a herd of 16 cows by Hitscher, 

 showed the following differences : 



