Nutrition and The Immune System – The Keys to Profitable Livestock Production

By Ralco Nutrition

Herd health is a key driver of profitability in today’s production environment. Maintaining health is extremely challenging, particularly as management systems become more intensive and profit margins are squeezed. Disease robs profits and productivity by reducing growth, increasing deads, lightweights and culls, and adding drug and vaccine costs. A healthy and robust immune system protects profits and animal welfare by minimizing the incidence and effects of disease.

The immune system is the body’s natural defense mechanism designed to combat invasion by microorganisms, including bacteria, viruses and fungi.  A responsive immune system improves animal health and welfare. Understanding how to build a healthy immune system is important for large and small producers alike to maximize productivity, welfare and profits. 

This paper provides a short review of the immune system and discusses how proper nutrition can build a robust immune system that responds quickly and appropriately to diseases.

The Immune System

The immune system is a well orchestrated system of specialized cells and proteins that defend the body against bacteria, viruses and other pathogens. The immune system is constantly on alert to defend against the first sign of invasion by harmful organisms. 

The immune system has two arms that have different functions and work at different times to provide a complete defense against disease:  the Innate Immune System (rapid defense) and the Adaptive Immune System (life-long immunity).

Innate Immune System

The first line of defense against the myriad of pathogens that assault the body is the Innate Immune System.  The innate immune response occurs within minutes of invasion. The innate immune system does not require prior exposure to the pathogen nor does it provide life-long immunity like a vaccine. 

The innate immune system has two components.  First, the body has physical and chemical barriers that prevent pathogens from entering. The skin and mucous membranes are physical barriers to microbial invasion.  The eyes, nose and mouth are protected by fluids or sticky mucus that captures microbial invaders. The gastrointestinal tract defends itself with stomach acid, mucus, and constant movements called peristalsis that flush invaders out of the intestine.  Together, these defense mechanisms are called the first line of defense.   

However, despite these defenses, microbes often manage to enter the body.  At this point, the second aspect of the innate immune system is activated called inflammation.  When pathogens breach the first line of defense, cells are damaged.  Dying cells release specialized chemicals that trigger the automatic response of inflammation.  Immune cells called neutrophils and macrophages (Fig 1) move to the infection site and destroy the invading microorganisms. 

Fig 1.  Cells of the immune system.

 Modified from www.irvingcrowley.com/cls/allcells.jpg

Adaptive Immune System

An amazing aspect of the immune system is its ability to remember enemies that it has encountered in the past and to respond much more quickly the next time the invader is seen again.  This is a hallmark of the Adaptive Immune System.  The cells of the adaptive immune system are called lymphocytes (Fig 1).  When lymphocytes encounter an invading organism, they have the ability to release antibodies (specialized proteins) that “mark” that organism for destruction by other cells.  This process takes seven to ten days.  This time is needed to allow the lymphocytes to multiply and produce large numbers of antibody-producing cells.  Once antibodies have been made, the adaptive immune system remembers that invader often for a lifetime.  If the organism is encountered again, the adaptive immune system will respond very quickly to produce antibodies and remove the invader.  It is likely that the invader will be destroyed before there are any signs of disease.  This is the type of immunity that is developed by vaccination.

Building a Robust Immune System

The ability of the animal to prevent disease infection is a delicate balancing act between the invading organism and the immune system.  Animals are particularly susceptible to disease when they are under stress.  Stressors include the birthing process, transport, mixing, poor diet, extreme temperatures, and antibiotic misuse.  Stress reduces immune function and predisposes animals to infection.  A strong and robust immune system will mitigate the effects of stress and allow animals to continue to grow despite disease challenges. 

Vaccination and development of lifelong immunity is an important part of disease management in herds and flocks. However, vaccines are expensive and may not be available for all strains of disease or for the less virulent invaders that reduce productivity.  As such, we are reliant on the animal’s innate immune system to maintain health and productivity. 

Nutrition is the key to a healthy immune system.  Appropriate nutrition can reduce the incidence and effects of disease.  There are four main building blocks of a healthy immune system:

• High quality diet with micronutrients for stressful periods and disease outbreaks
• Colostrum management to protect the newborn animal
• Anti-oxidants to promote lung and gut health
• Disease-ready immune system

High quality diet and micronutrients

A high quality diet provides energy and basic nutrients like protein, fat, fiber, vitamins and minerals, for optimal growth and development.  Like all cells of the body, immune cells require these basic nutrients to do their jobs and multiply when necessary.  Additional nutrients are needed for production of specialized immune proteins and other factors.  Of greatest interest for supporting the immune system are the vitamins and minerals. 

Several vitamins and minerals are important for immune system support.  Vitamin E is a powerful anti-oxidant that is present in the membranes of cells.  Vitamin E boosts immunity, increases antibody production, and improves lymphocyte function.  Vitamin E has been shown to reduce clinical mastitis in dairy cows and to improve the phagocytic activity of neutrophils.  Selenium is a component of an important anti-oxidant enzyme that works in synergy with Vitamin E.  Tissue stores of selenium and Vitamin E are rapidly reduced during infections.  These two components must be replenished during such stresses to maintain optimal disease defense. 

Vitamins A, C and D are also involved in immune system function.  Adequate levels are critical for optimum function.  Vitamin C increases the number of white blood cells and increases production of interferon, an important immune molecule that fights viruses.  Zinc and copper are needed for immune cell function also.

Colostrum protects the newborn

The immune system is not fully mature at birth.  Newborns are dependent on colostrum, the first milk produced, for immune protection.  Colostrum contains factors which are necessary for survival, including readily digestible energy that replenishes reserves and maintains body temperature.  Colostrum provides fluids and growth and immune factors.  The immune factors include antibodies, immune cells and immune regulation molecules.  These factors protect the newborn against diseases and participate in maturation of the neonatal immune system. 

While antibodies are often the main focus of discussions on colostrum, it is important to note that there are several other immune factors in colostrum that are critical for development of the immune system and the gastrointestinal tract.  These factors include anti-bacterial molecules, nucleotides, and anti-inflammatory factors. 

An often overlooked but important function of colostrum is to reduce gut inflammation after birth.  The newborn gut is sterile at birth, but it is immediately bombarded by bacteria, food components, and environmental contaminants during the birthing process.  Gut inflammation reduces the barrier function of the gut and alters nutrient absorption.  Colostrum contains immune factors that suppress gut inflammation and allows the neonatal gut to freely absorb energy and other nutrients.

A recent study showed that replenishing colostrum immune and growth factors shortly after birth significantly improved growth of low birth weight pigs.  Recent concerns about “failure to thrive” nursery pigs may be related to inadequate colostrum intake.

Fig 3. Effect of First Pulse® D (Ralco Nutrition, Inc.) on low birth weight “disadvantaged” piglets. The average weaning weight of First Pulse® D (FPD) pigs was +0.5 lb more than untreated pigs at 18 days after birth.

Gut health

Maintaining a healthy gastrointestinal tract is most important for animal growth and development.  A healthy gut allows maximum nutrient absorption and is a barrier against disease.  A major component of the immune system is located in the gut, called the gut associated lymphoid tissue (GALT).  Several aspects of gut health can be improved by nutrition.     

The newborn gastrointestinal tract is rapidly colonized by bacteria from the mother and the environment after birth.  This microflora develops over time into a stable population of over 400 bacterial species.  These bacteria provide vitamins and enzymes that salvage energy from indigestible carbohydrates.  They compete with disease-producing bacteria and stimulate immune system maturation.  For a healthy gut, the microflora needs to favor the beneficial bacteria, Lactobacillus and Bifidobacterium.  A healthy gut microflora has been shown to control several pathogenic bacteria, including Salmonella, E. coli and Clostridium. Improving the gut microflora can be accomplished by feeding a fermentable carbohydrate called a prebiotic.  Prebiotics selectively stimulate the growth of the beneficial bacteria.  Hemicellulose fiber is a unique and highly effective prebiotic that is selectively metabolized by Bifidobacterium, which produces byproducts that feed the Lactobacillus.  Probiotics (also called direct-fed microbials) are live bacterial cultures containing beneficial bacteria and they support the beneficial bacterial populations in the gut. 
   
Normal metabolism produces highly reactive, damaging molecules called free radicals.  The immune system also produces free radicals to destroy invading pathogens.  Free radicals damage cells and tissues is they are not rapidly neutralized.  Anti-oxidants are key dietary components that neutralize free radicals and prevent tissue damage.  Important dietary anti-oxidants are vitamins C and E, selenium, zinc, flavonoids, and herb essential oils, such as oregano essential oil.  Supplementation of diets with anti-oxidants is essential for lung and gut health.   

Because of their immature immune system, young animals are highly susceptible to infections caused by Salmonella and E. coli.  These bacteria colonize the intestine by attaching to gut receptors that have exposed sugars molecules.  To prevent this attachment, it is possible to disrupt bacterial binding by adding products containing mannan oligosaccharide (MOS) to the diet.  MOS acts as a “decoy” receptor for these bacteria and prevents gut colonization.  Because these bacteria do not attach to the mucosal surface, they are flushed from the intestinal tract.  Approximately 70% of pathogenic Salmonella and E. coli are susceptible to MOS.

Disease-ready immune system

A disease-ready immune system is “armed” and ready to act when there is the threat of a microbial assault.  An early, rapid and robust response often controls the infection before there are clinical signs of disease.  Many of the components of a disease-ready immune system have been discussed earlier.  However, another component that can enhance the immune system is ß-glucan.  ß-glucan is a component of yeast cell walls that can be added to diets, often in the form of hydrolyzed yeast cells.  Immune cells have specific receptors for ß-glucan.  When these receptors are bound by the ß-glucan, immune cells become primed and ready for defensive action. 

Natural plants and herbal extracts are potential alternatives to traditional antibiotics.  Essential oils, such as oregano essential oil, have powerful anti-microbial activity for many bacteria, but spare the beneficial bacteria cited above.  Oregano essential oil has been shown to improve sow feed intake, increase the number of piglets born, weaning weights, and improve broiler growth and liveability on farms with enteric challenges like coccidiosis.  These substances also have powerful anti-oxidant properties and they may provide protection from free radicals in the gut.

Conclusions

Herd health is one of the most important contributors to profitability of a livestock operation.  Infectious diseases negatively impact animal performance and welfare.  The immune system is the body’s natural defense against disease.  It is a complex and highly regulated system of cells and proteins that provide rapid protection against the infectious assaults that animals encounter daily.  Nutritional support for the immune system is important for maintaining peak protection from disease. Understanding how nutrition builds a healthy immune system allows producers to implement the most effective nutritional programs for their herds. Prevention of disease through nutrition is the key to herd productivity, animal welfare and producer profits.

Contact information:
Dr. Marnie Mellencamp, Director of Immunology
T: 507-337-6827, E: marnie.mellencamp@ralconutrition.com
www.ralconutrition.com