Relationship between somatic cell count and intramammary infection of the half udder in dairy ewes

A total of 1382 milk samples from half udders of three breeds of ewes (686 Assaf, 422 Churra, and 274 Castellana) were collected aseptically at midlactation from 18 flocks in the Castile-León region of Spain. Bacteriological tests were carried out on the samples to ascertain the status and type of IMI. Somatic cell counts were determined for all samples after bacteriological analysis. Analysis of variance showed significant effects of breed, IMI status, flock nested within breed by milking type, organism within IMI status, and interactions of breed by milking type and of breed by organism. The most frequent bacterial groups were staphylococci, especially coagulase-negative staphylococci, followed by streptococci, micrococci, and yeasts. The SCC response was related to the bacterial group involved in the IMI; coagulase-negative staphylococci showed significantly lower SCC values than those for coagulase-positive staphylococci and streptococci. Highest percentages of IMI by major pathogens and highest SCC, both in the absence of IMI and in staphylococcal IMI, were in Assaf ewes. The threshold of 300,000 cells/ml allowed 81% of the half udders to be correctly classified according to IMI status. However, the existence of breed differences in SCC response and IMI type could make the use of specific SCC thresholds for each breed advisable.