Milk samples were taken daily or twice weekly, and blood samples twice weekly, from six clinically healthy
dairy cows. Acetone concentration was determined by a new headspace gas-chromatographic method
that proved to be suitable in terms of practicality, sensitivity and precision. The concentration of acetone
in milk was closely correlated with that in blood (r² = 0,967). There was no relationship between lacteal
acetone concentration and either somatic cell count or bacterial infection. In both blood and milk there were
fluctuations in acetone concentration that were synchronous between the six cows. The fluctuations were
apparently cyclic, with a period of approximately 10 d. Such fluctuations have not previously been reported.
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