Minerals and the Immune System

Selenium (Se) is an essential trace mineral for health and normal immune function in both animals and humans, with Se and vitamin E being important antioxidants and sharing many biological activities (Ewing, 2007), (McDonald, 2011), (Paul, 2014).  Seleno-proteins are present in every cell type and protect the host from oxidative stress in various ways. Additionally, Se stimulates the production of IgM antibody-producing cells, it helps protect some tissues from poisonous substances such as arsenic, cadmium and mercury and is necessary for the repair of DNA (Paul, 2014), (Ewing, 2007).

Numerous studies have shown that selenium-deficient cattle have a greater incidence of retained placentas compared to cattle receiving adequate Se, with Arthington (2022) explaining that retained placentas are closely linked to the animal’s immune system because of the resulting inflammatory responses associated with the expulsion or retention of the placental membranes.  Selenium supplementation has also been found to reduce the recovery time in cows inflicted with metritis.   A study conducted by Harrison et al. (1986) found that metritis-inflicted cows receiving supplemental Se had fewer uterine recovery days when compared to cows not supplemented with Se when inflicted with metritis. It has also been reported by McDonald (2011) that Se supplementation of cattle and sheep at pasture can prevent “Ill Thrift” (a condition causing weight loss and even death) and in some instances, supplementation resulted in dramatic increases in growth and wool yield.

Every tissue within the animal body has been found to contain zinc (Zn) (McDonald, 2011), with the trace mineral having an essential role in the immune system in addition to being involved in wound healing (Ewing, 2007).  Zinc is known to be a component of over 200 enzymes and proteins which are necessary for protein synthesis, carbohydrate metabolism and the configuration of DNA and RNA (Kegley, 2016).  These Zn compounds are necessary for rapid cell proliferation and protein synthesis when the specific immune system is activated.  Prasad (2008) and Spears (1991) confirm that Zn is crucial for the normal function and development of cells mediating innate immunity, neutrophils and NK cells, phagocytosis, and cytokine production.   If an animal is deficient in Zn, it affects the immune system and is associated with loss of appetite and delays in wound healing.  With research  (Chirase, 1991), (Paul, 2014), (Spears, 1991) suggesting that the provision of higher concentrations of Zn above maintenance recommendations can be beneficial to the animal’s health during disease.

The benefits of Zinc supplementation in livestock have been well studied with Chirase et al. (1991) investigating the effect of Zn supplementation on feedlot steers challenged with a respiratory virus, where they found that the supplemented animals had an improved rate of disease recovery.  A trial conducted by Spears and Kegley (2002), investigating fed steers with no added Zn compared to supplementation with 25 mg Zn/Kg DM from zinc oxide and two different zinc proteinates, revealed that all supplemental Zn sources increased average daily gain as well as carcass quality grade.  It was also observed that lymphocyte blastogenesis and humoral antibody titres after IBR (Infectious Bovine Rhinotracheitis) vaccination did not differ among the different Zn supplements during the growing period.  In another study (Spears, 1991) it was found that stressed steers supplemented with Zn had an increase in antibody titres to the BHV-1 (Bovine Herpesvirus 1) vaccination compared to steers not being supplemented.  They also found that Zn supplemented steers experienced a greater dry matter intake compared to the control animals.  The effects of Zn fortified milk fed to newborn calves were investigated by Prasad and Kundu (1995) where it was found that Zn supplementation resulted in greater immunoglobulin (antibody) responses to antigen challenge.

Copper (Cu) performs numerous functions in the animal body and a deficiency affects the innate immune response.  It was observed by Boyne and Arthur (1986) that Cu deficiency resulted in a significant reduction in the neutrophil killing of C. albicans, phagocytic activity, nitroblue tetrazolium reduction (an estimate of free radical production), superoxide dismutase activity, and neutrophil viability.  When cattle were made Cu deficient in a study by Ward et al. (1993) they reported a reduced cell-mediated immune response.   Also, a reduction in serum IgM concentration following disease exposure in copper-deficient animals was reported by Paul (2014), and Enjalbert et al. (2006) discovered that an inadequate Cu status (based on plasma Cu concentrations) was associated with poor calf health and performance.  The importance of adequate Cu in the diet of livestock for overall health was confirmed by Stabel et al. (1993) as they suggested that copper-deficient animals are at a greater risk of infection compared to nondeficient animals.

Most iron (Fe) present in the animal body is found in haemoglobin, and deficiency affects the formation of this compound.  When the need for Fe increases, after prolonged haemorrhage or during pregnancy, then haemoglobin synthesis may be insufficient, resulting in anaemia.  Anaemia caused by a deficiency in Fe is mostly found in rapidly growing sucklings because the Fe content in milk is usually very low (McDonald, 2011).   Svoboda (2004) reported that Fe deficiency impairs the peripheral lymphoid compartment and may be associated with increased susceptibility to infectious disease and impaired immune mechanisms in piglets.  Although a deficiency in Fe is not common in older animals, McDonald (2011) suggests that increased supplementation of Fe is required when high levels of copper are used for growth promotion.

It has been shown that chromium (Cr) influences both immune function and energy metabolism and is present in small amounts in all animal tissues. However, the practical significance of Cr supplementation in the nutrition of livestock is still being investigated and although no recommendations for dietary levels have been made (McDonald, 2011), research has identified situations in which Cr supplementation might have a commercial application, e.g. during periods of stress, both environmental and metabolic (Ewing, 2007), (NRC, 2016), (Paul, 2014).

Chromium has been shown to have beneficial effects on health and production in animals (NRC, 2016), with supplementation reducing serum cortisol and increasing serum IgM (antibodies) and total immunoglobulins (Chang, 1992).  Steers were fed varying levels of Cr (0, 0.1, 0.2, or 0.3 mg Cr/kg DM) in a study conducted by Bernhard et al. (2012), who reported chromium-supplemented steers had improvements in dry matter intake, feed efficiency and performance within the first 28 days (animals would have been under significant nutritional and physiological stress at this time), and supplemented cattle maintained these advantages throughout the remainder of the trial.

An animal’s requirements for Cr may become more critical at times of stress, malnutrition, and blood loss.  McDonald (2011) reported positive responses to supplemental Cr where animals were under physiological stress, in addition to reports of an increased immune response, energy status, dry matter intake and milk yield in primiparous cows (have been pregnant or given birth once), and reduced morbidity in calves.  The benefits of Cr supplementation were further proven in a trial by Moonsie-Shageer and Mowat (1993) where they reported Cr supplementation decreased morbidity.  Overton (2014) also verified that dairy cows fed Cr during the transition period and early lactation had improved immune function, increased milk production, and decreased cytological endometritis.