THE EFFICACY OF IN-LINE MEASUREMENT OF QUARTER MILK ELECTRICAL-CONDUCTIVITY, MILK-YIELD AND MILK TEMPERATURE FOR THE DETECTION OF CLINICAL AND SUBCLINICAL MASTITIS

In-line sensors were developed for measuring quarter milk electrical conductivity (QMC) to detect mastitis in dairy cattle. The sensors were built into the milking claws of a six-point open tandem milking parlour, in which 65 cows were milked daily. For individual cows, deviations were calculated between averages of the 20 highest values of QMC, measured every 5 s during milking. Over a 12-month period, 2-monthly bacteriological examinations, cell counts of quarter milk samples and observations for clinical mastitis served as references for the conductivity measurements. High and low thresholds for QMC were determined in order to detect severe (clinical) mastitis and subclinical mastitis, respectively. The first should be considered for treatment during lactation and the latter for dry cow therapy. The lowest running average QMC was defined as a "reference quarter" for each cow after each milking. A quarter indicated severe mastitis if its running average QMC deviated in excess of 15% from the reference quarter and if actual QMC was 20% over the running average of the reference quarter during two successive milkings. In considering dry cow therapy, cows were selected if the running average of QMC deviated greater-than-or-equal-to 10, 15 or 20% from the running average of the reference quarter during at least five milkings in the last 2 months of lactation. Automated data collection of daily milk yield and milk temperature in addition to QMC established the severity of mastitis. All cases of clinical mastitis (25) were detected by the high threshold values and 50% of the cases of subclinical mastitis and secretion disturbance were detected. Using the low threshold during the last 2 months of lactation, 50% of the cows were selected for dry cow therapy. In 24% of the cows recommended for treatment, there were no signs of subclinical mastitis in the quarter milk samples.