Streptococci as the new dominant aetiological factors of mastitis in dairy cows in north-eastern Poland: analysis of the results obtained in 2013-2019.

The objective of our study was to evaluate prevalence of selected bacterial and fungal pathogens of mastitis in dairy cattle in north-eastern Poland. Our study was conducted from 2013 to 2019 in 1,665 clinically and sub-clinically infected quarter milk samples (2013, n = 368; 2014, n = 350; 2015, n = 290; 2016, n = 170; 2017, n = 173; 2018, n = 224; and 2019, n = 90). The isolation and identification of the pathogens were performed in keeping with generally accepted microbiological procedures. In 2013, mastitis was most commonly caused by Staphylococcus aureus (24%), Streptococcus spp. (22%), Streptococcus agalactiae (12%) and coagulase-negative staphylococci (11%). In 2014, the most common pathogens were Streptococcus spp. (25%), Staphylococcus aureus (18%) and coagulase-negative staphylococci (10%); in 2015, 2016, 2017, 2018 and 2019, Streptococcus spp. (from 39-49%) were the most frequent strains isolated from the quarter milk samples. Other pathogens were isolated occasionally (below 15% in all years). In conclusion, the role of environmental bacteria has been gradually increasing in the Warmia Province. The importance of infectious pathogens has been decreasing, indicating the efficacy of the applied preventive programmes and a need for the development of new programmes targeting environmental pathogens.