New advances in epizootiology and control of ewe mastitis

The lactation (or annual) incidence of clinical mastitis in the ewe is generally lower than 5%, while the prevalence of subclinical mastitis is variable and ranges from less than 10 to 50% or more. Staphylococcus aureus is the most frequent bacterium responsible for clinical mastitis (from 20 to at least 60%). Coagulase-negative staphylococci are the principal causative agents of subclinical mastitis (30–95%), mainly in dairy ewes. Somatic cell counts (SCC) represent a valuable tool for prevalence assessment and screening. At an individual level, the use of several successive SCC allows the efficient detection of subclinical mastitis and is a good predictor of persistance. Healthy udders regularly show a SCC value lower than 500000 cells/ml throughout the lactation period; values for subclinically or chronically infected udders usually exceed one million cells/ml. At the flock level, bulk milk SCC can be used to determine the overall intramammary infection prevalence, with a good coefficient of determination (r2=0.845). Using SCC or the California Mastitis Test, and clinical examinations, ewes to be culled or treated can be identified. Immediate or delayed culling and intramammary antibiotherapy at drying-off are the main measures for the elimination of intramammary infections. Drying-off intramammary antibiotherapy is increasingly being performed in dairy ewes, as it provides a good bacteriological cure rate. Prevention is mainly directed against infections involving mammary sources, and includes milking machine control, milking routine optimisation, and post-milking teat disinfection. Control measures should take into account the peculiarities of dairy sheep breeding (e.g. flock size, seasonality, cost–benefit ratios, etc.).