Exploring pathogen-specific somatic cell patterns in dairy ewes during early lactation

Abstract

The postpartum period is a critical period for mastitis susceptibility in dairy ewes, yet the species-specific effects of mastitis pathogens on milk SCC and differential inflammatory cell counts (DICC) remain largely unknown. Therefore, this study investigates pathogen-specific impacts on microscopic SCC and DICC in milk and colostrum from Lacaune dairy ewes during early lactation. A total of 586 colostrum and milk samples were collected from 50 ewes (100 udder halves) at 6 time points: on the day of parturition and at 1, 3, 7, 15, and 30 d postpartum. Milk and colostrum samples were examined through bacteriological analysis and species-level pathogen identification using MALDI-TOF MS, along with microscopic SCC and DICC measurements using precise DNA-specific cell counting procedures. Non-aureus staphylococci and mammaliicocci (NASM) were identified as the primary etiological agents of IMI, with Staphylococcus xylosus, Staphylococcus simulans, and Staphylococcus chromogenes being the most frequently isolated species. Among NASM species, S. simulans IMI resulted in the highest increases in SCC and neutrophil percentages, supporting its classification as a major mastitis pathogen in dairy ewes. In contrast, S. xylosus and S. chromogenes triggered mild or negligible inflammatory effects and could therefore be classified as minor mastitis pathogens. In addition, multiparous ewes had higher SCC than primiparous ewes, possibly due to the persistence of IMI. Furthermore, colostrum samples showed high SCC, predominantly composed of lymphocytes. Although our research provides insights on somatic and differential cell counts and the bacteria associated with IMI in dairy ewes during early lactation, its limitation to a single flock reduces generalizability. Further, comprehensive studies are needed to better estimate the effects on SCC, DICC, and their practical applications.

Keywords: dairy sheep; intramammary infection; mastitis; somatic cell count.