Pathogen profile of clinical mastitis in Irish milk-recording herds reveals a complex aetiology

Effective mastitis control requires knowledge of the predominant pathogen challenges on the farm. In order to quantify this challenge, the aetiological agents associated with clinical mastitis in 30 milk-recording dairy herds in Ireland over a complete lactation were investigated. Standard bacteriology was performed on 630 pretreatment quarter milk samples, of which 56 per cent were culture-positive, 42 per cent culture-negative and 2 per cent contaminated. Two micro-organisms were isolated from almost 5 per cent of the culture-positive samples. The bacteria isolated were Staphylococcus aureus (23 per cent), Streptococcus uberis (17 per cent), Escherichia coli (9 per cent), Streptococcus species (6 per cent), coagulase-negative Staphylococci (4 per cent) and other species (1 per cent). A wide variety of bacterial species were associated with clinical mastitis, with S aureus the most prevalent pathogen overall, followed by S uberis. However, the bacterial challenges varied widely from farm to farm. In comparison with previous reports, in the present study, the contagious pathogens S aureus and Streptococcus agalactiae were less commonly associated with clinical mastitis, whereas, the environmental pathogens S uberis and E coli were found more commonly associated with clinical mastitis. While S aureus remains the pathogen most commonly associated with intramammary infection in these herds, environmental pathogens, such as S uberis and E coli also present a considerable challenge.