[Factors affecting cell counts in milk from individual cows (author's transl)]

The number of somatic cells was determined in samples from approx. 700 cows in 70 herds, altogether 2570 samples. The average cell count was 250 thousands per ml with range from 7 thousands to 5 mill. The data were analysed with respect to effect of age of the cow, stage of lactation, and test day yield. The analyses showed that the cell count was strongly affected by age and yield. The effect of yield is removed by multiplying the recorded cell count by milk yield (cell count in thousands per ml times milk yield in kg congruent to total cell count in mill.). The cell count increases approximately linearly by increasing age of the cow up to 9--10 years, when it is about five times as large as for two-year-old cows. This increase is partly caused by a higher frequency of infection in older cows, but there was a distinct trend in the same direction even for cows which were noninfected when the sample was collected. After elimination of the effect of yield there was a slight drop in the cell count by advancing lactation.