Bulk tank milk somatic cell counts in dairy herds with different bovine viral diarrhoea virus status in Poland

•We examined the effect of BVDV infection on bulk tank milk somatic cell counts (BMSCC).•No statistically significant effect of BVDV infection on BMSCC was found.•An increase in herd size was associated with a significant decrease in BMSCC.•A slight increase of BMSCC was observed in the summer time compared to the winter time.

The aim of the study was to examine the effect of bovine viral diarrhoea virus (BVDV) infection on bulk tank milk somatic cell counts (BMSCC). Twenty nine dairy farms supplying milk to a dairy in Eastern Poland were recruited for the study. Bulk milk ELISA and RT-PCR were used to determine the BVDV infection status and the presence of PI animals in the farms. The BMSCC mean values for the BVDV seronegative (218.7 × 103 cells/ml; SD: 89.8) and seropositive (214.9 × 103 cells/ml; SD: 74.0) herds did not differ significantly. To assess the relationship between BVDV infection and BMSCC a multilevel mixed-effects linear model was used. No statistically significant effect of BVDV infection on BMSCC was found. The mean values of BMSCC for the herds with PI individuals measured before (230.1 × 103 cells/ml, SD: 64.9) and after (223.3 × 103 cells/ml, SD: 62.4) the PI removal were not statistically different. An increase in herd size was associated with a significant decrease in BMSCC. An increase in BMSCC was observed during summer (from May to September) compared to during winter (from October to April).