VARIATIONS OF MILK CONSTITUENTS l6j 



middle of May. Under the known existing condi- 

 tions of the food and environment of cheese-factory 

 cows, there was thus a change from dry food of 

 an indifferent character, mainly straw or poor hay 

 without grain, to a highly succulent food of a most 

 palatable kind. It is probable also that the changes 

 in the environment of the cows from confinement 

 in barn and yard to the freedom of pasture exercised 

 a beneficial, physiological influence. 



AMOUNT OF CASEIN IN MILK 



The percentage of casein in normal milk varies 

 quite widely, though much less than in case of 

 milk-fat. In the single milkings of individual cows, 

 we have found casein as low as 1.59 per cent and 

 as high as 4.49 per cent. The highest percentages 

 were found in the case of cows far along in lacta- 

 tion and giving only small amounts of milk. In 

 the case of individual herds of cows, the percentage 

 of casein ranged from 1.79 to 3.02. In the case of 

 milk consisting of a mixture of the milk of several 

 different herds, the percentage of casein varied from 

 1.93 to 3.00. 



The conditions which influence variation of casein 

 in milk, so far as they are of special interest to us 

 here, are (i) breed, (2) stage of lactation, (3) 

 change from stable to pasture, and (4) effects of 

 drouth. 



Influence of breed of cows on percentage of 

 casein in milk. The following- results illustrate, in 

 general, the variation of casein in the milk of different 

 breeds of cows : 



