92
Modulation of innate immune function and phenotype in bred dairy heifers during the periparturient period induced by feeding an immunostimulant 60 days prior to delivery
The purpose of this study was to evaluate the effect of an immunostimulating feed additive on innate immunity and health events during the periparturient period in dairy heifers when mammary immunity is suppressed. From 60 d prepartum through d of calving, supplemented heifers (n=20) received OmniGen-AF® daily and were compared with unsupplemented controls (n=20). Blood leukocyte innate immune activity (phenotypic markers, phagocytic activity, and reactive oxygen species (ROS) production) was measured prior to feeding (60 d prepartum), 30 d later, and on d 1, 7, 14, and 30 postpartum. Health parameters and milk production were measured at calving and early lactation. Expression of CD62L among leukocytes from supplemented heifers was greater during the periparturient period than controls. Specifically, on d 1 postpartum, mean % of neutrophils exhibiting CD62L surface markers was 95.3% for OmniGen-AF® treated heifers vs. 91.4% for controls (P < 0.10), and the % decreased from 98.3% 30 d prepartum to 91.4% on d 1 postpartum among controls (P < 0.05); values for supplemented heifers did not decrease. Likewise, leukocyte phagocytic activity against Escherichia coli and Staphylococcus aureus was greater in heifers supplemented with OmniGen-AF®, e.g., on d 30 prepartum and d 7 postpartum, mean % of monocytes from supplemented heifers exhibiting phagocytic activity against E. coli were 11.7 and 11.3%, whereas values for controls were 7.3 and 7.4% (P < 0.10). In controls, phagocytosis decreased from 13.7% 60 d prepartum to 7.3 and 7.5% on d 30 prepartum and d 7 postpartum (P < 0.05), but values for supplemented heifers did not decrease over time. Conversely, ROS production in response to PMA and killed S. aureus stimulation was greater among control heifers compared with supplemented animals, e.g., the quantities of ROS generated in response to S. aureus lysate on d 1 and 7 postpartum were 68.8 vs. 51.9 and 56.1 vs. 41.3 units (P < 0.05). Supplemented heifers exhibited fewer deleterious health events (retained placenta, displaced abomasum, ketosis, udder edema, death) than controls (1.25 vs. 1.93 /heifer) and a lower rate of new cases of mastitis (9.6% vs. 23.2%); however, no significant differences were observed in overall prevalence of mastitis, milk SCC, or milk production. Results demonstrated a positive role of OmniGen-AF® in amplifying leukocyte antibacterial activity during the periparturient period and support the continued study of dietary supplementation to enhance mammary gland health in dairy cattle.
Keywords: dairy heifer, innate immunity, periparturient period