Prevalence and aetiology of subclinical mastitis in dairy ewes of the Madrid region

A bacteriological sun ey for studying the prevalence and aetiology of subclinical mastitis was carried out in 22 dairy sheep flocks of the Madrid region. A total of 1128 milk samples were collected from 564 ewes. 17 Manchega flocks (5 hocks had mechanical milking and 12 flocks had hand milking) and 5 Assaf flocks (all had mechanical milking) were included in the study. Prevalence of subclinical mastitis in the different flocks ranged from 4.5-67% of the glands and 9-83% of the animals, with an average of 21 and 34.%, respectively. Prevalence of subclinical mastitis in Manchega flocks with mechanical milking was lower than those with hand milking (P<0.05). Assaf flocks had higher prevalence rates than Manchega flocks with mechanical milking (P<0.05). Increase of subclinical mastitis as lactation proceeded was observed only in Assaf ewes. Prevalence of subclinical mastitis was lower in primiparous Manchega and Assaf ewes than those which had two of more lactations. CMT score 1(+), with the best combination of sensitivity and specificity values, can be recommended as a threshold value for detecting subclinical mastits. Coagulase-negative staphylococci were the most prevalent bacteria, representing 68% of the isolates. Staphylococcus epidermidis (40%), was the most prevalent species followed by Staphylococcus haemolyticus, Staphylococcus simulans and Staphylococcus xylosus. Corynebacterium was the second bacterial group in importance according with the distribution among flocks, being isolated from 41% of the flocks and representing 10% of the isolates, which suggests for these bacteria, a clinical significance higher than that traditionally considered as responsible for subclinical mastitis in sheep. Subclinical mastitis seems to be, as deduced from the high prevalence observed in this study, an important health problem for milking sheep hocks in the Madrid region. (C) 1999 Elsevier Science B.V. All rights reserved.