SOMATIC-CELL COUNTING IN MILK - FLOW CYTOMETRIC MEASUREMENT WITH FOSSOMATIC-5000

In recent years the fluorescence optical principle has been expanded b y flow cytometry. The FM 5000 (Foss Electric A/S, Denmark) is an integ rative component of the Integrated Milk Testing system. Preservation g ives the same effects with the FM 5000 as with other instruments using the fluorescence optical principle. Cooled raw milk can be counted up to 2 days after sampling. Potassium dichromate and bronopol can be re commended as preservatives. New settings for repeatability give signif icantly lower variance between countings. In ''standard precision'' mo de repeatability values are in accordance with requirements of modern time. In ''fixed repeatability'' mode repeatability can be kept below certain limits. With a counting time of 14 s per sample the ''Kiel sam ple'' mode gives an excellent repeatability. The setting ''dynamic rep eatability'' increases grading accuracy. A comparison with the Fossoma tic 360 gives a correlation coefficient of 0.994 in linear scale. This means nearly identity. Carry-over effects are low and can be avoided by a special control of the instrument. Linearity is comparable to oth er instruments. Intercomparison trials showed, that on levels up to 50 0,000 cells/ml repeatability in terms of its standard deviation (s(r)) is in most cases less than 10,000 and in no case higher than 15,000. Between levels of 500,000 and 990,000 s(r) it reaches 20,000. Reproduc ibility in terms of its coefficient of variation (CVR) showed values o f 7-8% on cell levels around 450,000. A biased masuring scale can be c orrected by calibration using a sufficient number of reference samples . The FM 5000 gives easy setting possibilities to gain excellent accur acy. Under field conditions sampling errors may influence the high qua lity of the counting result.