Effects of oral calcium bolus supplementation on immune cell calcium flux and functionality in primiparous and multiparous dairy cows

The objectives of this study were to (1) characterize calcium levels and immune function in primiparous and multiparous animals following oral calcium bolus supplementation, and (2) determine differential responses of boluses containing a lower dose of calcium than traditionally used in primiparous animals on calcium levels and immune function. Jersey X Holstein crossbred animals (N=104) were enrolled within 24 h of parturition from a single commercial dairy in West Texas. All animals were blocked by time relative to calving (0-8h, 9-16h, and 17-24h) and randomly assigned to treatment. Calcium boluses were composed of a mixture of calcium chloride, calcium sulfate, and calcium propionate. For objective 1, animals were assigned to control (CON) no calcium supplementation, or a series of 2 calcium boluses given 24 h apart containing 44 g of calcium. Objective 2 treatments included control (CON) no calcium supplementation, a series of 2 calcium boluses given 24 h apart containing 44 g of calcium, or a series of 2 calcium boluses given 24 h apart containing 22 g of calcium. Blood samples were collected via coccygeal venipuncture from each animal on day 1(<24h), 2, 3, 5, and 7 relative to parturition. Blood was used to analyze total serum calcium, serum haptoglobin, neutrophil intracellular calcium, neutrophil intracellular calcium after stimulation with an environmental E. coli, neutrophil L-selectin surface expression, and neutrophil phagocytic and oxidative burst activities. Data were analyzed using Proc Mixed in SAS (SAS 9.4, Cary, NC). The oral calcium x parity data indicated a tendency (P=0.078) for a treatment difference on basal intracellular neutrophil calcium and a treatment difference (P=0.017) on E. coli stimulated intracellular neutrophil calcium. There was a parity x DIM effect for neutrophil oxidative burst intensity; however, there were no other parity x DIM (P ≥ 0.144) or parity (P ≥ 0.122) effects on other functional neutrophil variables. In primiparous animals, there was a treatment difference (P=0.005) for E. coli stimulated intracellular neutrophil calcium among animals given 44g of calcium but no treatment difference (P=0.341) on basal intracellular calcium. There was a treatment tendency (P=0.061) for primiparous animals given 44g of calcium to increase neutrophil phagocytosis intensity. There was also a treatment difference (P=0.048) for neutrophil oxidative burst intensity in primiparous animals given 44g of oral calcium. Supplementing animals with 44 g of oral calcium for 2 days increased intracellular neutrophil calcium and had a mild effect on neutrophil function. Reduced intracellular neutrophil calcium plays some role in reduced neutrophil function, but other factors contribute to the impaired neutrophil function and oral calcium can only restore some of the diminished function. Further, a low dose of 22 g of oral calcium in primiparous animals was not effective at increasing intracellular neutrophil calcium or restoring some of the impaired neutrophil function related to parturition.