INTRODUCTION
The importance of essential micro-nutrients (trace minerals and vitamins) on livestock productivity has been recognised for a considerable period. Recently, the importance of trace mineral nutrition on immune competence and the effectiveness of vaccination programs have received increased attention.
Morbidity and mortality of stock due to disease causes economic losses and reduced genetic gain. A major cause of wastage is the inability of stock to respond immunologically to antigen challenges (eg bacteria and viruses).
Stock are able to overcome infections by developing an elaborate immune system which recognises and destroys foreign harmful substances (ie antigens).
“The immune system initiates responses to destroy antigens”
To ensure a comprehensive immunological response to a foreign substance and to optimise the outcomes of vaccination programs, the immune system must not be compromised by inadequate nutrition. That is, to meet present and future disease challenges the immune system requires sufficient energy, protein and macro-minerals and an adequate concentration of micro-nutrients (ie trace minerals and certain vitamins).
Whilst certain vitamins and trace minerals (ie vitamin E, copper, zinc and selenium) have attracted considerable research, other trace minerals (eg chromium, iron, manganese and iodine) should not be overlooked and it is probable that they will receive more attention in future studies.
This article examines the important role that vitamin E, copper, zinc and selenium play in providing an immune system capable of responding to and defeating the challenges of antigens.
IMMUNE SYSTEM RESPONSES
The immune system comprises of three integrated components that collectively initiate immune responses to protectthe health of cattle.
“Responses include non-specific and specific responses”
NON SPECIFIC RESPONSES (NATURAL AND ADAPTIVE)
This initial response involves physiological barriers (eg mucous membranes) body functions (eg secretions in the intestinal and respiratory tracts) and self clearing mechanisms (eg vomiting and diarrhoea) which require proper nutrition and hydration. These activities require trace minerals to be active and effective.
SPECIFIC RESPONSES(INNATE AND ADAPTIVE)
These highly complex responses involving humoral and/or cell mediated immune functions require trace minerals to be effective.
- Humoral immune responses involve the systematic production and secretion of antibodies produced by lymphocytes (special category of leukocytes) to inactivate specific antigens.
- Cell mediated responses involve lymphocytes that stimulate and recruit phagocytic activity which find and eliminate abnormal body cells that contain specific antigens (ie bacteria, protozoa, viruses).
Deficiencies and excesses of trace minerals have a direct effect on the immune system and can make the animal more susceptible to infection. Specific ways that nutrition affects the effectiveness of the immune system include:-
- Anatomical development of lymphoid tissue
- Mucous/lung surfactant production
- Synthesis of immunologically active substances
- Cellular proliferation, activation and movement
- Intracellular killing and the detoxification of free radicals produced by phagocytic cells
- Modulation and regulation of immune processes
Producing phagocytes, antibodies and lymphocytes to provide an effective immune system requires proper energy, protein and mineral nutrition (Table 1)
Table 1. Nutrient requirements of the immune system – a partial list of functionsa.
| ITEM | NEEDED FOR: |
| Energy Protein | Rapid proliferation of immune cellsCell replicationSynthesis of antibodies and cytokines |
| Minerals(Cu,Zn,Mn,Se,Fe,S)b | Antioxidant systemsEnergy productionProtein synthesisMembrane integrity (physical barrier to pathogens) |
| Vitamins(A,D,E,C,B complex)c | Antioxidant systemsCellular differentiationEnergy productionProtein synthesisMembrane integrity |
aAdapted from Nockels and Whittier (1995).
bCu = copper, Zn = zinc, Mn = manganese, Se = selenium, Fe = iron, S = Sulfur
cVitamins D, C, and the B complex are needed in the immune system; however, no specific cattle data are available.
“Micro-nutrients are vital for effective immune systems and responses:
TRACE MINERALS AND THE IMMUNE SYSTEM
Proper nutrition has been well recognised as a pre-requisite for a healthy immune system. Although all nutrients (Table 1) are important for immune function, the roles of certain trace minerals and vitamins are extremely important.
Most trace minerals are essential for enzyme activity including enzymes for energy production, protein synthesis and cell replication (Table 1). Additionally, several trace-mineral dependant enzymes act specifically within the immune system such as those removing free radical produced by phagocytes.
The trace minerals and vitamins most often associated with immune function and subsequently have received the most research are copper, zinc, selenium and vitamin E.
“Micro-nutrients play an important role in immunology interactions and vaccination programs”
TRACE MINERAL AND VACCINATION
Due to various factors (vaccination protocols, health of stock, stress etc) the vaccination of stock does not always induce an effective immune response in some stock. The vaccination response also depends on good nutritional status of the livestock before and after the vaccination process.
“Good nutritional status fends off infection and enhances immune function”
Micro-nutrients (copper, zinc, selenium) have also been recognised for their role in proper functioning of the immune system and improving the resistance to disease via vaccination.
TRACE MINERAL DEFICIENCIES
Trace mineral that can compromise the immune system are frequently divided into two groups:
Primary – a deficiency resulting from the inadequate intake of an essential trace mineral necessary to support the physiological functions associated with the particular trace mineral.
Secondary – a deficiency resulting from the consumption of a trace mineral(s) which limits the pre or post absorption of an essential trace mineral thus limiting the physiological functions associated with that trace mineral.
In highly developed agricultural systems primary deficiencies resulting from the reduced intake of trace minerals are relatively uncommon. Unfortunately seasonal variations and challenges frequently occurring in semi tropical and warm temperate pasture production systems found in Queensland and northern NSW result in a higher incidence of primary deficiencies. This is the result of reduced intake of total digestible nutrients (TDN) from lower quality pastures and crops. The situation can be further compounded due to the presence of antagonists, eg bore water high in minerals that cause secondary deficiencies.
“Marginal deficiencies result in reduced immune performance”
The general approach for either deficiency is often addressed by increasing the supplementation of the most obvious mineral deficiencies providing mixed results. Trace mineral supplementation involves only small amounts of minerals and requires careful analysis, monitoring and supplementation to avoid imbalances or excesses both of which are antagonistic to mineral absorption and subsequently to effectiveness of the immune system.
ROLE OF MICRO-NUTRIENTS
As suggested, nutrition to increase the defence mechanisms of livestock to combat infection has received increased interest in recent years. In challenging beef production systems, certain micro-nutrients (vitamin E, copper, zinc and selenium) when properly supplemented have been shown to enchance the immunity of livestock and increase the resistance to disease.
Stock requirements for micro-nutrients are influenced by several interacting factors including age, stage of pregnancy, growth and lactation. Studies have indicated that the amount required for optimal immune response is greater than the recommendation for the production functions (ie growth, pregnancy, lactation and reproduction), that is, cattle can have sufficient trace mineral intake for the production functions but insufficient for optimal immune function.
COPPER (CU)
Copper has been shown to be important for immune system function. Cu metabolism affects the function of several classes of immune system cells, particularly those involved in producing antibodies.
“Copper is involved in many aspects of immune responsiveness”
Copper is also vital for the activity of an enzyme responsible for the removal of toxic free radicals from the body (Cu – Zn superoxide dismutase) as well as the activity of phagocytes. Copper aids in the scavenging of free radicals thus preventing oxidative damage to tissues.
Copper deficient animals exhibit reduced numbers of circulatory neutrophils and decreased activity of peripheral macrophytes (ie copper deficiency reduces the activity of phagocytes). Copper deficiency also reduces the activity of the humoral and cell mediated immune systems.
Copper deficiencies are most common when stock have low intakes of low quality feed (ie primary deficiency). Secondary deficiencies occur as a result of the presence of copper antagonists (eg sulphur, molybdenum, and/or iron) which substantially hinder the absorption and metabolism of Cu.
ZINC (ZN)
Zinc plays an important structural and activator role with numerous enzymes and is important for antibody production. Zinc is vital for the proper functioning of lymphoid tissue for cell production.
A Zn deficiency results in atrophy of the thymes and an increase in leukocyte count (evidence of infectious disease) with reduced numbers of lymphocytes. In several studies, zinc supplementation resulted in greater antibody responses to an antigen challenge.
SELENIUM (SE) AND VITAMIN E
The trace mineral selenium is very important to specific and non specific immune processes. A main function of Se is to protect biological membranes from oxidative degeneration due to the presence of free radicals which can lead to tissue breakdown. Se deficiency results in immunological suppression whereas supplementation results in augmentation and/or restoration of immune function.
Se deficiency inhibits the resistance to microbial and viral infections, neutrophil function, antibody production and the proliferation of lymphocytes.
“Greatest benefits are found when Se is combined with vitamin E”
Studies have shown that combining the two micro-nutrients increased the defence against disease (eg mastitis and metritis) and decreased the duration of infection. The majority of research supports that a combination of vitamin E and Se improves the killing ability of neutrophils.
Selenium is closely linked with vitamin E as an additional line of defense against free radicals. The antioxidant roles of Se and vitamin E share common biological activities via the metallo-enzyme, glutathione perioxide. This enzyme is responsible for protecting cellular membranes from oxidative damage.
“Forages are the main source of Se and vitamin E and soils low in selenium produce plants low in selenium”
Selenium deficiency can occur in soils in various locations in semi tropical and tropical environments although actual locations should be evaluated on an individual basis.
Table 2: Relative Bioavailability of Some Mineral Sources
| ELEMENT | SOURCE | BIOAVAILABILITY |
| Selenium | Sodium selenite | High |
| Copper | Copper oxideCopper carbonateCopper sulphate | LowIntermediateHigh |
| Zinc | Zinc oxideZinc sulphate | HighHigh |
FEEDING LEVELS
SELENIUM
The National Research Council (NRC) recommends feeding selenium at a level of 0.3 ppm (mg/kg) on the total diet. The Se status of cattle is best determined by blood testing because the absorption of selenium can be decreased by substances in the intestinal tract such as high concentrations of sulphates or nitrates from water and feedstuffs.
Some forms of selenium are more available (ie bioavailability) than other forms. Sodium selenite is a more common source of supplemental seleniums.
VITAMIN E
The NRC recommendation for vitamin E is 150 IU/day for dry cows and 300 IU/day for lactating cows, however, the beneficial effect of vitamin E against disease requires greater intakes than the NRC recommendation. The level of supplementation will depend on the quality of food fed to stock. Stock on matured pasture and/or stored conserved forages may require twice the amount of the recommended vitamin E intake.
The amount of vitamin E in a plant decreases as the plant matures and can be low in stored conserved pastures and crops. Livestock consuming greater than 50 per cent of their forage from above-average quality pastures probably do not need supplementation with vitamin E.
The various forms of supplemental vitamin E have different bioavailabilities to the animal and the feeding level will vary with the different forms of vitamin E.
COPPER
The NRC recommendation suggests that copper be supplemented at 10ppm in the total diet but studies have shown that 20ppm of supplemental copper in the total amount seems to have the greatest positive impact on the immune system. As with selenium, different forms of copper have different availabilities to the animal (Table 2). Note: both the form and type of administration of copper needs to be carefully assessed to prevent excesses leading to toxicity and mortalities. Young stock are more sensitive to copper toxicity than adult stock.
The amount of available copper absorbed by stock can be decreased when dietary iron, sulphur, molybdenum or zinc intake is high.
ZINC
The NRC recommendation level for zinc is 40 ppm in the total diet. Zinc fed at 40-60 ppm in the total diet has been shown to enhance immune functions. Zinc sulphate has a higher bioavailability than zinc oxide (Table 2). Other forms of zinc that have high bioavailability are zinc proteinate and zinc methionine.
FEED MANAGEMENT
Micro-nutrients should be thoroughly mixed in the ration to ensure all stock consume adequate amounts and avoid excesses. Some trace minerals can be injected (eg copper and selenium). Trace mineral blocks may not allow the consumption of adequate intakes of micro-nutrients. Trace minerals provided as dry powder are convenient to mix with grain-protein and fortified molasses supplements.
“Nutritionists can assist in the formulation of suitable mineral mixtures”
To overcome primary and secondary deficiencies and avoid excesses, it is important to formulate rations based on a feed history and knowledge of specific nutritional deficiencies.
Feed history involves the analysis of feeds and water samples to optimise trace mineral intakes, eliminate antagonistic factors and avoid mineral toxicity. Tissue samples (blood and liver) by your local veterinarian can confirm the incidence of trace mineral deficiencies.
MANAGEMENT PRACTICES
Studies indicate that the effects of micro-nutrients on the immune system although beneficial can be variable. The interactions between trace minerals, animal production status and disease resistance are extremely complex. Factors that can affect responses include the duration and concentration of trace mineral supplementation, physiological status of the stock, the presence of antagonistics, environmental factors and the influence of stress on mineral metabolism.
Supplementing stock, particularly heifers with Se, Cu and Zn on poor pastures can be very beneficial.”Weaners are a deserving group for trace mineral supplementation”
To prevent disease and infection challenges, efforts should be made to support the immune system of young stock. Multiple factors at weaning (eg transportation, yarding, separation from dams and processes such as branding/dehorning/ vaccination) cause significant stress which reduces the effectiveness of the immune system.
Effects of stress can be compounded by several factors (eg removal of milk, decreased feed intake, different feeding regime) which can hinder the weaners ability to overcome nutritional deficiencies and increase the susceptibility to infection.
Studies suggest that Cu, Zn and Se supplementation should be increased in the diets of weaners and all stock nutritionally challenged by low intakes of poor quality feeds.
BOTTOM LINE
To avoid compromised immune systems and optimise immune responses to disease challenges, proper nutrition involving energy, protein, macro minerals and micro nutrients is essential.
A properly functioning immune system will reduce the incidence and duration of infections and enable vaccination programs to be more effective at preventing health problems and reduced economic returns due to morbidity, mortality and reduced productions and increased pharmaceutical and veterinarian expenses.
“A proper health program needs an effective nutritional program”
Properly fed stock are more resistant to many bacterial and parasitic infections. This is due to a number of interrelated factors including better body tissue integrity, more antibody production, more immunity to disease, greater detoxifying ability and increased blood regeneration.
Micro nutrients involving balanced trace mineral intakes and interrelationships are an important part of optimal herd health, productivity and immune function.
Proper feed and nutritional management is necessary to avoid primary and secondary deficiencies and optimise the use of trace minerals. Most importantly trace mineral intake should be balanced and excesses prevented to allow the immune system to function effectively. That is, like most nutrients, trace minerals should not be over supplemented.
In challenging pasture production systems found in northern NSW and Queensland, focussing on improvements in micro-nutrient nutrition to improve herd health and immune competence benefits production. It is possible that studies involving other trace minerals will challenge health and feed management programs in the future.
“Ideally involve a veterinarian and nutritionist when addressing micro nutrients deficiencies”
FURTHER READING
“Health – Passive immunity and Colostrum” ABBA Brahman News, June 2015 pp. 36-39.
“Health – Immune Sysytem and Vaccination” ABBA Brahman News, December 2014 pp. 46, 48-50.
BRAHMAN NEWS SEPTEMBER 2016 ISSUE #192 PAGE 48
By Alex Ashwood
