Postpartum dairy cows experience host-damaging inflammation and heightened risk for infectious disease, resulting in reduced animal well-being, lost production, increased antimicrobial use, and premature culling. At the same time, cows also experience hypocalcemia, a hallmark of the immediate postpartum period when calcium (Ca) demands for lactation increase significantly. Blanket supplementation with Ca early postpartum has become widespread. However, Ca administration during sepsis and endotoxemia is known to increase systemic inflammation, prolong antimicrobial treatment, and increase organ damage and mortality in monogastrics. Yet, early lactation dairy cows are often blanket treated with Ca, particularly when suffering from acute inflammatory disease (e.g. mastitis or metritis). It is critically important to study the risks and benefits of supplemental Ca in postpartum cows experiencing inflammation to understand if this practice exacerbates the magnitude and duration of host-damaging inflammation.

Our global hypothesis is that Ca availability modulates the inflammatory response and that iatrogenic alteration of this physiological response is potentially detrimental to postpartum cows. Our objective is to assess the effect of therapeutic use of Ca on the magnitude and resolution of systemic inflammation and to elucidate the fate and sequestration of circulating Ca during an intravenous (IV) inflammatory challenge with lipopolysaccharide (LPS) in postpartum dairy cows. This in vivo challenge allows us to model an acute inflammatory response that is predictable and reliable. Then, we will investigate the dose-response relationship between Ca availability and the magnitude of immune cell activation and inflammation in immune cells of postpartum cows. In the requested 1-year funding period, we will address the following 2 specific aims:
1A) Measure the effects of Ca supplementation during an in vivo LPS challenge on the magnitude, duration, and resolution of the inflammatory response in postpartum dairy cows, and
1B) Analyze the systemic fate and sequestration of supplemental Ca during this LPS challenge.
2) Describe the in vitro Ca dose-response of cytokine production and global transcriptome effects in bovine innate immune cell populations.

We will achieve aims 1A and 1B in a matched-pair randomized control study. LPS-challenged cows in the treatment group (n=8) will receive IV Ca to maintain eucalcemia for 12 h following LPS, while paired LPS-challenged cows in the control group will receive saline solution instead of Ca. Plasma cytokine concentrations and speed of resolution of inflammation will be quantified. Urine, fecal, milk, and peritoneal fluid Ca concentrations will be measured and compared. Aim 2 will be completed using monocytes and granulocytes isolated from 10 postpartum cows. Dose-response to different Ca concentrations is determined in vitro, and cytokine production, Ca kinetics, and global transcriptome changes in response to LPS will be compared.