Parenterally administered pegbovigrastim alters leukocyte counts, granulocyte functions, and uterine cell population in healthy postpartum dairy cows

This study aimed to evaluate the effects of a single postpartum administration of pegbovigrastim, a recombinant bovine granulocyte colony-stimulating factor (rG-CSF), on peripheral leukocyte profiles, granulocyte function, and uterine cytology in healthy Holstein dairy cows. We hypothesized that rG-CSF would enhance leukocyte counts and granulocyte function without adversely affecting uterine immune cell composition. Twenty-three cows between 19-23 days in milk were randomly assigned to receive either rG-CSF (n = 12) or saline (n = 11). Blood samples were collected on the day of injection and on Days 3, 6, 10, and 21 post-treatment to assess total and differential leukocyte counts. Granulocyte phagocytosis of fluorescein isothiocyanate (FITC)-labeled Staphylococcus aureus and oxidative burst capacity following PMA stimulation were evaluated using flow cytometry. Vaginoscopy and transrectal ultrasound examinations were conducted at each time point, and uterine cytobrush samples were collected from a subset of cows for cytological analysis. Compared to controls, rG-CSF-treated cows exhibited a significant (2-3 fold) increase in total leukocytes and neutrophils (P < 0.01) on Days 3, 6, and 10. Monocyte counts were also elevated (4-fold; P < 0.01) on Day 3. Granulocyte functional assays revealed increase in oxidative burst (P = 0.04) and phagocytic activity as well as capacity (P = 0.01) that peaked on Days 3 and 6 post-treatment, respectively, following rG-CSF treatment. Furthermore, uterine samples from treated cows showed higher proportions of neutrophils (Days 6, 10, and 21) and macrophages (Day 10) compared to controls (P < 0.01). In conclusion, a single dose of rG-CSF in early postpartum cows induces transient leukocytosis and enhances granulocyte function. The observed increase in uterine neutrophils and macrophages suggests that rG-CSF could be explored further for its potential as a local immunomodulatory agent during the postpartum period.