Effects of maintaining eucalcemia following immunoactivation in lactating Holstein dairy cows

Periparturient hypocalcemia is a common metabolic disorder and it is ostensibly associated with negative health and production outcomes. Acute infection also markedly decreases circulating Ca, but the reasons for and consequences of it on physiological and immuno-logical parameters are unknown. Objectives were to evaluate the effects of maintaining eucalcemia on pro-duction, metabolic, and immune variables following an intravenous lipopolysaccharide (LPS) challenge. Twelve multiparous lactating Holstein cows (717 +/- 20 kg of body weight; 176 +/- 34 d in milk; parity 3 +/- 0.2) were enrolled in a study containing 2 experimental periods (P); during P1 (3 d), cows consumed feed ad libitum and baseline values were obtained. At the initiation of P2 (4 d), cows were randomly assigned to 1 of 2 treat-ments: (1) LPS administered (LPS-Con; 0.5 mu g/kg of body weight LPS; n = 6) or (2) LPS administered + eucalcemic clamp (LPS-Ca; 0.5 mu g/kg of body weight LPS; Ca infusion; n = 6). Cows were fasted for the first 12 h during P2. After LPS administration, ionized Ca was determined every 15 min for 6 h and every 30 min for an additional 6 h and intravenous Ca infusion was adjusted in LPS-Ca cows to maintain eucalcemia. Blood ionized Ca was decreased 23% for the first 12 h postbolus in LPS-Con cows, and by design, Ca infusion prevented hypocalcemia. To maintain eucalcemia for the 12 h, 13.7 g of Ca was infused. The total Ca deficit (including Ca not secreted into milk) accumulated over the 12 h was 10.4 and 20.2 g for the LPS-Con and LPS-Ca treatments, respectively. Mild hyperthermia (0.8 degrees C) occurred for similar to 6 h post-LPS administration relative to P1. From 6 to 7 h postbolus rectal temperature from LPS-Ca cows was increased (0.6 degrees C) relative to LPS-Con cows. On d 1 of P2, milk yield decreased (61%) in both treatments relative to P1. Relative to LPS-Con cows, milk yield decreased (15%) in LPS-Ca cows during P2. Overall, circulating LPS-binding protein continuously increased postbolus, and at 24 h LPS-binding protein levels in LPS-Ca cows were increased (80%) relative to LPS-Con cows. During P2, serum amyloid A increased (4-fold) in both treatments relative to P1. Administer-ing LPS initially decreased circulating neutrophils, then cell counts progressively increased with time. Calcium infusion decreased neutrophil counts (40%) from 9 to 12 h postbolus relative to LPS-Con cows. Neutrophil function, as assessed by oxidative burst and myeloper-oxidase production, did not differ due to treatment. In summary, maintaining eucalcemia (via intravenous Ca infusion) during an immune challenge appeared to intensify inflammation and adversely affect lactation performance.