Immunophenotyping of somatic cells during lactation in Frizarta dairy ewes: effect of lactation stage and parity and association with total bacterial count

The aim of this study was to characterize the physiological variation of somatic cell count (SCC) and milk somatic cell subsets in relation to total bacterial count and milk production parameters, in mastitis-free local Greek ewes. To this end, we studied the SCC, daily milk yield and composition, milk somatic cell subset distribution and total bacterial count in the milk of first and second parity Frizarta ewes, at different lactation stages. As there is a total lack of evidence for differential milk somatic cell distribution in local Greek ewes, we chose to study the Frizarta breed, one of the most promising local sheep breeds, extensively reared in Western Greece, highly productive and well adapted to geoclimatic conditions. Partial correlation analysis was performed between SCC and somatic cell subtype populations with milk yield, composition and total bacterial count. Total SCC in Frizarta ewes ranged between 35 and 74 × 10³ cells/ml and was significantly influenced by lactation stage and parity number. Neutrophils and lymphocytes were the most abundant immune cell types followed by mammary epithelial cells and macrophages. A positive association of bacterial count with neutrophils and macrophages and a negative association with lymphocytes were observed. Finally, a negative association between total bacterial count with daily milk yield was detected. Our data forms the basis for understanding how parity and stage of lactation affects different immune and epithelial cell populations in the milk of healthy Frizarta ewes and can be used in future studies investigating the effect of the health status on differential cell count in ewe milk.