Bacterial species and their associations with acute and chronic mastitis in suckler ewes

Acute mastitis in suckler ewes is often detected because of systemic signs such as anorexia or 23 lameness whereas chronic mastitis, characterised by intramammary abscesses with no 24 systemic disease, is typically detected when ewes are inspected before mating. The aims of 25 the current study were to identify the species and strains of culturable bacteria associated with 26 acutely diseased, chronically diseased, and unaffected mammary glands to investigate 27 whether species and strains vary by state. To investigate acute mastitis, 28 milk samples 28 were obtained from both glands of 14 ewes with acute mastitis in one gland only. To 29 investigate chronic mastitis, 16 ovine udders were obtained from two abattoirs; milk was 30 aspirated from the 32 glands where possible, and the udders were sectioned to expose 31 intramammary abscesses which were swab sampled. All milk and swab samples were 32 cultured aerobically. In total 37 bacterial species were identified, four from acute mastitis, 26 33 from chronic mastitis, and eight from apparently healthy glands. In chronic mastitis, the 34 overall coincidence index of overlap of species detected in intramammary abscesses and milk 35 was 0.60, reducing to 0.36 within individual glands; indicating a high degree of species 36 overlap in milk and abscesses overall, but less overlap within specific glands. 37 Staphylococcus aureus was detected frequently in all sample types; it was isolated from 10 / 38 14 glands with acute mastitis. In five ewes, closely related strains were present in both 39 affected and unaffected glands. In chronic mastitis, closely related Staphylococcus aureus 40 strains were detected in milk and abscesses from the same gland.