The immune system is a critical part of maintaining homeostatic balance in the animal and is often the system that is side-lined in favour of performance and growth. Stress (environmental, management or pathogenic) increases susceptibility to infectious disease and impairs animal performance. A function of the animals feed is to consistently provide nutrients that help improve the animals’ immunity and resilience to disease. Let us take a look at the role of 2 common macro-minerals, Calcium and Magnesium, in immunity:

1. Calcium is essential in the immune response for the activation of different white blood cells in innate immunity (Saltmarsh, 2008).
2. Calcium is important in the strength of the neutrophil oxidative burst, the killing response of the innate immune cells (Sweeney et al., 2014). 
3. According to the University of Bristol, Calcium represents the immediate inflammatory signal in wound healing before white blood cells. 
4. Ca influx is an essential mechanism in the activation of mast cells. Mast cells play an important protective role as well, being involved in wound healing, angiogenesis, immune tolerance and defence against pathogens (Saltmarsh, 2008).
5. Many ion channels in T-cells (acquired immunity) are regulated by calcium. Therefore, calcium plays a role in the activation and proliferation of T-cells (Badou et al., 2013).
6. Intracellular calcium stores decrease in peripheral blood cells (PBMC) before parturition, resulting in hypocalcemia. Therefore, maintaining blood calcium concentration through parturition can help sustain an active immune system (Kimura, Rheinhardt and Goff; 2006).
7. In a study by Kvidera et al. (2017), ionized calcium was found to be severely decreased (46%) following LPS administration. Other studies observed similar results (Griel et al., 1975; Elsasser et al., 1996; Waldron et al., 2003b). This decrease is presumably due to calcium’s involvement with immune system activation.
8. Hypocalcaemic cows are five times more likely to contract mastitis than cows that do not suffer milk fever (Chapinal et al., 2012).
9. Magnesium is an important modulator of intracellular free calcium ion concentration and intracellular pH. These are critical in determining cell contraction, secretion, motility, and proliferation (Brandao et al., 2012). 
10. Tam et al. (2003) reviewed the role of magnesium in the immune system. Magnesium deficiency was shown to increase pro-inflammatory cytokines and impair the efficiency of the innate and acquired immune response. 
11. Kubenam (2008) found that magnesium deficiency results in lower levels of IgG and IgA in serum, as well as lower levels of IgG in colostrum, depriving piglets of antibodies.
12. Trawinska et al. (2013) found magnesium supplementation resulted in a significant decrease in Enterobacteriaceae in sow faeces.

Calcium and magnesium on their own will not guarantee an efficient functioning immune system; however, as we can see from the research, they are vital tools in the complex pathways of the immune system. Both calcium and magnesium are macro-minerals that are incorporated in animal diets currently. Focusing more on the sources and bioavailability of these minerals provides us with a tool to help improve the efficiency and robustness of an animals immune system.