Milk differential cell counts in relation to total counts in Sardinian ewes

Milk samples from 40 primiparous Sardinian ewes were examined during a whole lactation period in order to evaluate the dynamics of somatic cell counts (SCC), differential cell counts (DCC) and bacteriological status of the mammary gland. Only four samples out of 240 were bacteriologically positive and this was confirmed by the geometrical mean of SCC being always below 200 000 cells per ml. DCC during lactation showed two different dynamics: one concerning polymorphonuclear neutrophil leucocytes (PMN) and macrophages, and the other one lymphocytes and epithelial cells. Macrophages and PMNs in particular showed a progressive increase as lactation went on, while lymphocytes and epithelial cells showed a uniform decrease during lactation. The relationship between SCC and DCC indicated that PMN was the only cell type increasing when SCC rose. The progressive increase of SCC during lactation in absence of infection was probably an effect of cell concentration owing to the physiological reduction of milk yield, while the increase of macrophages and PMN was very likely a consequence of immune mechanisms approaching the dry period. The results confirmed that DCC and particularly PMN rate could provide a more sensible method of identifying mammary inflammations, particularly in well managed herds with low levels of infections.