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Period of Lactation and the Direct Titratable Chloride Value of Milk

Department of Dairy Industry, Cornell University, Ithaca, New York

ABSTRACT

The following statements refer to the chloride value of milk as determined by the direct titration of the milk with silver nitrate, using potassium chromate as an indicator.

1. The direct titratable chloride value of milk was found to increase with the dilution of the milk and with decreased amounts of indicator. As the acidity of the milk increased, no influence upon the end point was found until after the casein had coagulated.
   
2. Differences between normal morning and evening milk were slight.
   
3. The fraction of the total milking of the quarter of the udder and the different quarters themselves had little effect on the chloride values of the normal milk from healthy cows.
   
4. The first and last milk drawn from quarters infected with mastitis was high in chloride and pH and low in titratable acidity, the middle portion often approached or fell within the range of normal mastitis-free milk. Wide variations were found between the different quarters in the case of cows infected with mastitis.
   
5. The chloride in milk from healthy cows fell very rapidly during the first few days of lactation, reached a minimum, increased slightly during the first 60 per cent of the lactation period, and then increased more rapidly, particularly during the last 10 per cent of the period.
   
6. A definite relation was found between the chloride value and the daily production of milk from healthy cows. A marked increase in chloride began when the production of Jersey and Guernsey cows fell below 15 pounds, and when the production of Holstein cows fell below 25 pounds of milk a day.
   
7. The milk from healthy Holstein cows tends to be higher in chloride than does the milk from healthy Jersey and Guernsey cows.
   
8. Gestation exerts a negating tendency on the increase in chlorides due to progressive lactation.