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The Leucocyte Content of Milk as Correlated with Bacterial Count and Hydrogen Ion Concentration for the Detection of Mastitis^*

Idaho Agricultural Experiment Station, Moscow, Idaho

ABSTRACT

This paper presents experimental data concerning the laboratory diagnosis of mastitis in cows. Aseptically drawn milk samples representing the individual quarters of each udder were used. The following conclusions appear valid:

1. Of all the laboratory methods used in this investigation, the leucocyte content of milk is the truest indicator of mastitis.
   
2. Bacterial counts on blood agar were more reliable for detecting udder infections than those on plain agar because plain agar often failed to produce distinct colonies from the organisms which were responsible for the infection.
   
3. Hydrogen ion determinations by the quinhydrone and Brom Cresol Purple methods correlate with other laboratory methods used to determine udder infections. The changes in reaction, however, are so slight, except in extreme cases, that the results are difficult to interpret.
   
4. The leucocyte count seems to be the most reliable index of udder infection, due to the enormous numbers of leucocytes encountered in milk from infected quarters, and the generally high leucocyte content of milk drawn from apparently normal quarters of the same udders. The fact that the leucocyte content of milk remains constant after it is drawn adds to its reliability.
   
5. Analysis of 758 leucocyte counts seems to warrant the conclusion that milk from normal udders usually contains less than 50,000 leucocytes per cc., whereas milk from infected udders almost invariably contains more than 100,000 leucocytes per cc.
   

^* Published by approval of the Director of the Idaho Agricultural Experiment Station as Research Paper No. 85.