Dr.R.N. Sreenivas Gowda
Former & Founder Vice Chancellor, Karnataka Veterinary, Animal And Fisheries Sciences University,(KVAFSU) Bidar, Former Director, Institute of Animal Health & Veterinary Biologicals, Bangalore, India, and Former- Professor and University Head: Dept. Of Pathology, Veterinary College, UAS, Bangalore, India
Among all livestock species, poultry production tops in the world, and poultry is reared to meet the demand of animal protein through eggs and meat at lowest prices. The producers often face several hurdles in rearing them, which depend on the utility type, the direction of use, and consumer requirements. For all these years, the aim was to increase production results, including weight gain in meat type chicken at shortest period and increase in number of eggs in layers, while trying to reduce feed intake. Besides good management and nutrition, control of infectious diseases is essential for the production of healthy poultry flocks, and this is generally achieved by extensive vaccination programs in combination with good management practices, including biosecurity measures to reduce the risk of infection.
The immunosuppression(IS) problem appears unnoticed in almost all the flocks and it is a hidden problem in the poultry industry. Despite of all sorts of management, nutrition and disease control but actual fact indicating the scale of the problem is difficult to find. Infection with pathogens and/or environmental factors, including management errors, can result in immunosuppression, and interactions between the two usually exacerbate the problem.
The biggest losses in poultry production are reflected in reduced growth and performance of individuals, reduced egg production and shell quality, increased morbidity and mortality rates, and greater susceptibility of immunocompromised individuals to secondary infections. Effective management strategies are key to minimizing the impact of immunosuppression in poultry.
What is immunosuppression?
Immunosuppression in chickens refers to a weakened or impaired immune system, making them more susceptible to diseases. This can be caused by various factors, including infectious agents like viruses, mycotoxins, and stress, often stemming from poor management practices, often these appear as sub clinical and unnoticeable.
Immune system in the Chicken
The immune system in chickens consists of primary immune organs and sac lymphoid tissue. The primary immune structures are 1). The primary immune organs thymus, where T lymphocytes are produced and mature; 2). The bursa of Fabricius, where B lymphocytes mature, and 3)The primary immune organs. The bone marrow, where blood cell precursors are produced. In addition, during the embryonic development of chickens, the source of maternal antibodies is the yolk sac.
Primary lymphoid organs mainly act as a center for the production and maturation of adaptive immune cells. Secondary lymphoid tissues specialize in controlling immune responses. They activate immune effector cells, such as lymphocytes. After maturing in primary lymphoid organs, T and B lymphocytes re-enter the bloodstream and colonize secondary lymphoid tissues to facilitate antigen presentation to lymphoid cells and initiate and regulate the adaptive immune response.
The main difference between the immune system in mammals and chickens is the lack of encapsulated lymph nodes. Instead, there is “diffuse” lymphoid tissue and its clusters in organizations such as Peyer patches, ceacal tonsils, and Meckel’s diverticulum. Lymphoid tissues include the spleen and mucosa-associated lymphoid tissues (MALT), also classified as the mucosal immune system (MIS). Lymphoid tissues in mucous membranes lining systems associated with nutrition (gut-associated lymphoid tissue—GALT), respiration (nasal-associated lymphoid tissue—NALT, bronchus-associated lymphoid tissue—BALT), and vision (conjunctiva-associated lymphoid tissue—CALT).
In chickens, these tissues are immunologically well-developed and are the first line of defense against pathogens. In about 20-wk-old chickens, the primary immune organs, that is, the bursa and thymus, are involute, and it is in the MIS that the humoral immune response occurs.
Chickens have 3 immunoglobulins (Ig) classes: IgA, IgM, and IgY. The chicken IgA and IgM are similar in structure to mammalian IgA and IgM. There are no analogs to mammalian IgE and IgD in chickens. IgM is associated with the primary immune response in chickens, and its monomer is a B-cell receptor.
Occurrence of immunosuppression
Immunosuppression in chickens, the weakening of their immune system, can be caused by various factors, environmental stressors, nutritional, poor management practices and infectious agents, dpecifically, viruses like Infectious Bursal Disease Virus (IBDV) and Chicken Infectious Anemia Virus (CAV) are major culprits, along with mycotoxins and other stress factors.
The chicken is more prone to immunosuppression caused by noninfectious and infectious causes:
- Noninfectious causes
In non-infectious conditions, IS is caused by various factors including environmental stress, nutritional deficiencies, and mycotoxins. These stressors can impair the immune system’s function, leading to increased susceptibility to infections.
- High density flocks
- Feed and water deprivation
- Frequent handling for weighing & vaccination handling
- Adverse environmental conditions ( Cold &Heat)
- Heat stress- summer months
- Managemental errors-frequent disturbances
- Various bacterial and fungal toxins in feed
- Infectious causes
These include various infectious agents caused by Virus, Bacteria and protozoan spps,
- Viral
- Infectious Bursal Disease Virus (IBDV)
- Chicken Infectious Anemia Virus (CAV)
- Marek’s disease(MDV)
- Avian Leukosis Virus (ALV),
- Reticuloendotheliosis virus(RE)
- Bacterial
- Mycoplasma (CRD)
- E.Coli
- Staphylococcus aureus (which can cause staphylococcosis).
- Parasite
Coccidial species are a subclass of obligate intracellular protozoan parasites belonging to the apicomplexan class, among which two groups, Cryptosporidium baileyi and Eimeria species, have been linked to immuno-suppression,
Subclinical Immunosuppression:
This refers to a weakened immune system that may not show any outward signs of illness but can still make chickens more susceptible to disease.
Effects of immunosuppression:
- Flock performance might have been substandard: well before the producer realized there was immunosuppression in the flock;
- Reduced growth and performance: Immunosuppression can lead to reduced weight gain, poor feed conversion, and lower egg production;
- Increased susceptibility to infections: Immunosuppressed chickens are more likely to develop severe and persistent infections;
- Increased morbidity and mortality: Immunosuppression can result in higher rates of disease and death within a flock;
- Secondary infections: Weakened immune systems can be more susceptible to secondary infections, exacerbating the problem;
- Treatments to control diseases: might have been less effective than expected;
- Routine vaccination programs against common diseases might have been less effective and needed to be modified or intensified to improve protection;
- Economic losses: Immunosuppression can have significant economic consequences for poultry farmers, including reduced production, increased treatment costs, and higher mortality rates.
Immunomodulation
Immunomodulation refers to the alteration of the host’s immune response to foreign agents and pathogens either by antibody stimulation (immune-stimulation) or inflammation suppression (immunosuppressant) in order to maintain the desired level of host immune-protection.
Objective of Immunomodulation
The preliminary objective of immunomodulation is to improve host resistance to external as well as internal attacks by the microbes or other infectious agents. The basic objectives of immunomodulation in domestic animals include:
- To trigger powerful and sustained immune response against disease causing microorganism
- To improve maturation of specific and nonspecific immunity throughout neonatal period besides insusceptible young animals.
- To augment local protective immune reactions at susceptible sites or gastro intestinal tract.
- To overcome the immunosuppressive effects of stress and environmental pollution
- To enhance duration and level of immune response following vaccination
- To maintain immune surveillance.
Immunomodulators
- These are the agents which specifically modulate immune system regulating immunity and disease resistance.
- In poultry it is specifically important as the growth, disease resistance, FCR, body weight gain production output mainly depends on the health and immunity of the chickens.
Feed nutrients and feed additives
Immune function is a complex system that requires higher concentrations of nutrients (amino acids, fatty acids, vitamins, and minerals) than those for productive traits. Besides, immunity is given first priority with regard to nutrient distribution among body functions. Protein and essential amino acids are vitally important for growth and antibody formation and a well-functioning immune system(fig.1.). This goal is achieved by supplementation with industrial amino acids such as methionine, lysine, arginine, tryptophan, and threonine to ensure adequate intake of limiting essential amino acids.
Fig ;1. Action of micronutrients on immune system
Nutritional immunomodulation: can be altered through incorporating some feed additives, such as photogenic plants, plant extract, prebiotic, probiotics, symbiotic, yeast, and enzymes, have reported immunomodulatory effects (Fig.2). It is widely recognized that beneficial microbiota—probiotics, lactic acid bacteria, and Saccharomyces cerevisiae, with its cell wall constituents glucan and MOS—and organic acids are necessary for immunity and gut health. The probiotic as immunomodulatory interventions show the prospect to improve Poultry tolerance to bacterial diseases such as salmonella, help detoxify aflatoxin, and decrease the hazards of nitrate.
Phytochemicals
Improving animal health and the GIT tract health are priorities in animal production other than reproduction. These are potential feed additives possessing multiple functions, Including anti-inflammatory, antifungal, antiviral, and antioxidative properties
Turmeric Rhizome Powder (TRP)
TRP in the diet significantly increased blood IgA, IgG, and IgM levels, and decreased the ratio of monocytes in 42-day-old broilers given SRBCs (sheep red blood cells) . RP supplementation increased the total secondary antibody titer against SRBCs in broilers and decreased the heterophils and lymphocytes ratio (H/L) under heat stress treatment
Cinnamon: Dietary supplementation of cinnamon extracted oil or leaves has shown to decrease coliform bacteria in the jejunum and large intestine and improve growth performance in broilers
Thyme: Thyme is the name for Thymus; thymol, carvacrol, p-cymene, and γterpinene are the major active components in the essential oils. Supplementation is in the form of essential oil orleaf powder. This essential oil improved cutaneous basophil hypersensitivity to phytohaemagglutinin P (PHAP) along with reducing the H/L ratio.
Essential oils (EOs): these are vital aromatic components, which are used as natural substitutes for antibiotic growth promoters(AGPs) in poultry feed. These have antimicrobial, antiviral, antifungal, antiparastic properties. Other benefits are, they act as appetite stimulant, improves enzyme secretion related to food digestion, and immune response activation
Byrates: Byrates stimulates digestive secretions (bile and mucus)while enhancing enzymatic activity In broilers, EO (essential oils) boost trypsin, amylase and jejunal chyme secretions as well as reduces the pathogens adherence (for example, E.coli and Cl. perfringens) to intestinal wall.
Conclusion
Knowledge on poultry immunity will facilitate the development of antibiotic alternative strategies to improve growth potential of poultry. Optimal combinations of various alternatives, coupled with good management and husbandry practices, will be the key to maximize performance.
Immunomodulation is widely acknowledged as alternative therapy for a range of diseases. Restoring of sufficient immune response is a robust therapeutic strategy to combat several ailments. With regular therapies for different illnesses, Immunomodulators containing extract derived as bioactive components in standardised dosages might be regarded as supplemental therapy/ adjuvant therapy to increase the quality production of eggs and meat.