Phagocytosis and reactive oxygen species (ROS) production by CH138 granulocytes isolated from blood, colostrum, and milk of Holstein cows during transition period.

This study investigated the functional activity of CH138 + granulocytes in the blood, colostrum, and transitional milk of Holstein cows throughout the transition period. Thirteen cows were assessed weekly, beginning three weeks before calving (W-3, W-2, and W-1), on the day of calving, and continuing to three weeks postpartum (W1, W2, and W3). Physical examination of the udder tissue, bacterial cultures, and blood immune function tests were performed. Microscopic Somatic Cell Count (MSCC), phagocytosis, and intracellular ROS production by CH138 + granulocytes in colostrum and transitional milk were measured weekly, from calving to W3. Disease incidence was recorded, with four cows developing metritis at W2. Mammary gland edema, affecting parenchymal tissue consistency, was the main physical finding. Non-Aureus Staphylococcus spp. dominated the bacterial isolates from the mammary secretions (67.5 %). MSCC was highest in colostrum and decreased postpartum. Bacterial culture rates peaked at calving; however, colostrogenesis limited the detection of clinical mastitis through specific examinations. Blood neutrophil function decreased at W-2 and W-1, likely increasing the risk of mammary infection and weakening the neutrophil response at calving. This immune suppression, which affects both the mammary gland and systemic immunity, was exacerbated by postpartum metritis. The findings showed heightened vulnerability to bacterial infection postpartum, which was linked to reduced cell viability and CH138 + granulocyte function. Neutrophil function in mammary secretions gradually improves post-calving, supporting immune recovery and declining infection rates. These findings provided valuable insights into the immune adaptations of CH138 + granulocytes in colostrum and transitional milk, enhancing understanding of mammary and systemic immune responses during the transition period.