Nutrition & Immunity

Importance of passive / maternal immunity

Comparision of live vs. killed vaccines

Active Immunity

Factors influencing the course of infection

Conclusion

Health management and Biosecurity are perhaps the most critical aspects of poultry production.  Today, with intensified approach towards poultry farming, it is becoming difficult to achieve adequate isolation and to ensure comfortable degree of protection against invading infection.  Maintaining optimum immune response  in the bird has become a major challenge and it starts with the breeder hen, then day-old-chick and continues throughout its life cycle.  Under today's prevailing problems such as respiratory complexes, complicated CRDs, increase in E.Coli and Salmonella infections etc and difficulty of treating the same with ever increasing antibiotic resistance, it is a challenge and at the same time, the need of the hour to enchance the immune status of the bird.

The ability of the bird to fight infection and disease is determined by its capacity to respond to invading pathogen. The body protects itself against foreign materials such as bacteria and virus through its immune system.  Invading organisms trigger the action of lymphocytes i.e., white blood cells or macrophages (scavengers in the body).  These lymphocytes are produced and programmed by BURSA & THYMUS called as B-cells & T-cells respectively.   B-cells migrate to spleen where they produce antibodies  on stimulation by antigen.  This is referred to as HUMORAL IMMUNITY.  The thymus, which is found in the neck of the bird, produces T-cells that work in cooperation with macrophages to kill invading bacteria or virus.  This is referred to as CMI (Cell Mediated Immune response).  Generally, humoral immunity is the main defense against bacteria, while CMI is critical for protection against virus.

A number of factors have been shown to have detrimental effect on the activity of immune system.  These include stress, toxins, diseases, nutrition, infectious pressure etc.  It is, therefore, essential to duly address these factors to maintain the immune system.  Of these factors, few can't be eliminated, rather can be minimised.  Eg.  Stress, Infectious pressure.  Mycotoxins are to be dealt with all seriousness, as the lowest so called 'safe level' can cause immunosuppression, specially the aflatoxins.

Nutrition forms the hub of efficient poultry farming, be it a broiler, breeder or a layer operation.  Industry is facing newer challenges in maintaining higher immune levels, apart from economic viability and higher productivity, of course, all are inter related.  Most of the research focus on poultry production is centered around determining and fine-tuning the vitamin, mineral and amino acid requirement of the bird.  It is inferred by all such development that we need to feed the bird for 'immunity' apart from optimal productivity.

Keeping broiler chicks as the focus some figures could be attributed to the immune system and it's cost.  During the course of maintenance some 1.17% of lysine requirement is used on the immune system.  This raises to approx. 6.71% during a disease challenge and this is taken as the expense of growth.  The highest priority for nutrients is the macrophages, which offer the 'front line' defense mechanism.  After the macrophages, come the B-Cells and then, the T-Cells.  The drawback with stimulating Macrophages is with their mode of action against invading antigen presenting surfaces.  Macrophages will engulf and destroy invaders by peroxidisation.  Although this is an extremely effective method of control, it also creates 'collateral' damage of the surrounding tissues with free radicles produced.  To reduce  the amount of tissue damage, antioxidants such as Vit.C, E & Selenium are beneficial.

The positive effect of high level of Vit.E on immunity is well established.  Vitamin E is an important biological anti oxidant having synergic action with Selenium.  Vitamin E is incorporated into the cell membrane and selenium in to the cytoplasm to protect the cell from oxidative damage, which is ongoing phenomenon specially under stress condition, which is never ending in poultry operation.  The fast multiplying immune cells need to be protected with higher level of Vit. E and Selenium in the diet.  It has been proven that Vit. E and Selenium prolong the CMI response, maintain the membrane integrity and favor the proliferation of T-Cells.  Additional supplementation of Vit. E becomes crucial specially during this time, inefficient absorption of fat-soluble  compounds limit the absorption of Vit. E and at the same time, most intense immunological pressure comes on to  young birds as they are exposed to pathogens for the first time through natural challenge and vaccination.

Gastrointestinal tract is a major interface between the host and environment and it is therefore the main site of pathogenic challenge.  Many of the pathogens from contaminated water or feed gain access to the system through gut.  Gut associated with immunesystem, hence become very important to present a first line of defense against invading pathogen.  Many of the probiotics are known to stimulate gut associated immune system by specific and non-specific means.  Yeast culture and Lactobacillus  species of organism are proven beneficial in this regard.  Recent interesting finding is that restricted feeding can increase immune response  by lowering insulin levels and increasing glucagon levels.

Day-old-chick, with inadequately developed immune system has to depend on the immunity passed by the mother.  This short-lived immunity, which is often referred as 'passive immunity', is through the immunoglobulins passed on to the chick from mother.  The success of passive immunity depends on adequate vaccination and antibody titer of breeding hens.  The higher the titer in the hen, the greater the transfer to the chick.  Specially, for diseases like NCD, IBD & IB, there is about 50% of transfer of titer from the breeder hen to the chick.  The most important factor in protecting all chicks seems to be the uniformity of titer in breeder hens.  So, the resistance power of chick is, to a greater extent, influenced by the mother.

Later in the life of chicken, the immunity is derived by active mechanism with vaccination program.   Vaccines are used to stimulate the bird's own immune system.  Vaccination is one of the more effective ways to prevent specific diseases.  This is why we vaccinate poultry;  so they are protected from explosive disease outbreaks.  Viruses stimulate the development of better immunity than other types of microorganisms; so most poultry vaccination are against viral diseases like Newcastle disease, infectious bronchitis, laryngotracheitis, fowl pox, and infectious bursal disease.  Disease producing microorganisms can be classified smallest to largest as viruses, bacteria, fungi, protozoa, and parasites.  All except the viruses are sensitive to drugs or antibiotics, so treatment against them is available when outbreaks occur.  Because viruses are resistant to drugs and antibiotics, their control is fully dependent upon prevention through sanitation, isolation and vaccination.

Vaccination is basically the introduction of a specific biological substance (antigen) into the bird to stimulate the formulation of a resistance or immunity to a particular disease.  Usually the biological substance is some of the live disease organisms that you want to protect the bird against. The presence of these organisms in the blood stimulates the body's defense mechanism to produce antibodies that attack the disease causing organisms when the bird is exposed to them.  Scientists have developed weakened (attenuated) forms of most disease causing viruses with little danger of causing the severe form of the disease.  Even the killed form of some disease causing viruses stimulate the production of antibodies.  In these cases, the 100 percent safely killed virus is used.  Short term protection against a particular disease can also be achieved by an antiserum that contains antibodies previously formed by animals that have been exposed to that particular disease, however it has limited practical application in birds.

So-called vaccination outbreaks do occur periodically.  The factors influencing vaccine response in poultry are many, mainly depending  on the host and environment.  Seldom are all factors considered when vaccination programs are initiated.  Ordinarily some protective immunity is produced when poultry are vaccinated, although the vaccine in itself cannot guarantee it.  Vaccination failures under field condition occur due to complex interaction of many factors viz. Stress, mycotoxins, latent form of immunosuppressive diseases, underlying nutritional deficiencies, vaccination storage conditions and vaccination procedures etc.  When vaccination failures occur, the total vaccination program should be reviewed.

MICROORGANISM:

• Virulence

• Infectious pressure

• New strains

BIRD:

• Age

• Type

• Immune status

• Immunosuppressive diseases

MANAGEMENT:

• Flock density

• Nutrition

• Water quality

• Litter management

• Ventilation

• Light

• Stress factor

• Biosecurity

Biosecurity   & Immunity are the key factors for efficient poultry production.  All efforts can be made to optimize the immunity and to prevent the diseases rather than 'firefighting' after infection takes the upper  hand.  Nutritional and Managemental factors are to be addressed for achieving higher level of immunity.