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Sections of Bacteriology and Dairy Husbandry, Michigan Agricultural Experiment Station, East Lansing, Michigan
ABSTRACT
Samples of milk were secured from individual cows from three herds, two of which showed streptococcic infection while the third showed no streptococcic infection. These samples were tested, organoleptically for salty flavor and for per cent chlorides. Fifty-six per cent and 90.9 per cent of the infected samples from the two infected herds were criticized for having a salty flavor. Twenty-five per cent and 20.5 per cent of the non-infected samples from the infected herds were found to have a salty flavor, as compared to 14.8 per cent of the samples from the negative herd, these latter being from cows almost dry or at least far advanced in lactation.
The averages of the per cent chlorides in the infected samples were 0.192 and 0.2263 for the two herds studied, with the non-infected samples of the same herds averaging 0.167 and 0.1694 per cent, respectively. The milk from the non-infected herd averaged only 0.1374 per cent chloride.
Milk from the infected cows of the two herds scored averages of 19.54 and 18.1 points while the milk from the non-infected cows of the same herds scored averages of 20.67 and 21.17, respectively. The milk of the non-infected herd averaged a score of 21.59.
Although the flavor of mastitis milk was not always salty, the majority of the samples were so criticized. Factors such as stage of lactation, milk yield, and extent of infection, undoubtedly have a marked influence upon the salty flavor of the milk.
The methylene blue test was run on streptococcus-infected and non-infected cow composite and quarter samples of milk. In addition, the leucocyte and bacteria counts of all samples were determined. The milk from the streptococcus-free cows was of higher quality, as determined by the methylene blue reduction test and the number of leucocytes and bacteria per cubic centimeter. The next highest quality of milk was produced by the non-infected quarters of streptococcus-infected cows.
A streptococcus infection in one, two or three quarters of a cow seemed to influence the quality of milk secreted by the non-infected quarters of the same cow. On this account the milk produced by non-infected cows was of higher quality than that secreted by the non-infected quarters of a streptococcus-infected cow.
The infected cow composite and quarter samples of milk were of lowest quality on the basis of the tests employed. They were of lower methylene blue class milk and contained the highest number of leucocytes and bacteria per cubic centimeter of milk. These facts are most important when dairymen are interested in the production of high quality milk.
The elimination from the producer's supply of milk from the streptococcus-infected cows in two herds resulted in an increase in the quality of the producer's milk.
Although most of the milk from streptococcus-infected cows had a salty flavor, high chloride content, high leucocyte and bacteria counts, and was of lower quality as determined by the methylene blue test, none of these determinations can be used alone to make an accurate diagnosis of streptococcic mastitis.
* Journal Article No. 228, n.s., Michigan Agricultural Experiment Station.
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