Efficacy of the Measurement of the Electrical Conductivity of Milk for the Detection of Subclinical Mastitis in Cows: Detection of Infected Cows at a Single Visit

Abstract

SUMMARY It has recently been shown that sub-clinical mastitis is a major cause of variations in the ionic composition of milk. It is therefore to be expected that resulting changes in milk conductivity would be a sensitive indicator of damage to the udder. Indeed there is an excellent correlation between infection of quarters and non-parallel day-to-day variations in conductivity. With continuous monitoring 98 per cent of infected quarters can be detected by this means. By re-analysing previous data we now show that even on a single occasion all severely infected quarters can be detected if one or more is 16 per cent higher than the lowest in that animal or if the level exceeds the conductivity of a 56 · 5 mM-NaCl solution. To aid in interpretation of herd conductivity measurements new data are also presented of the effects of early and late lactation, systemic illness, antibiotic treatment, blood in milk and the changes that occur during the course of a milking. As an example of the sort of data that can be obtained, on-the-farm values are presented of quarter conductivity measurements from a herd where sub-clinical mastitis was not recognized as a problem although the bulk cell count was about half a million. The results show that 17 per cent of cows were severely affected, 42 per cent mildly and 10 per cent would require more investigation. Acting on this information quarters with cell counts of 2 to 11 million were detected in half the cows.