IMMUNOMODULATION IN POULTRY UNDER STRESS CONDITIONS
Post no 1358 Dt 13 th August 2019
Compiled & shared by- DR RAJESH KUMAR SINGH, JAMSHEDPUR,9431309542,rajeshsinghvet@gmail.com
Introduction:
Modulation of the immune system denotes to any change in the immune response that can involve induction, expression, amplification or inhibition of any part or phase of the immune response. Thus, immunomodulator is a substance used for its effect on the immune system. There are generally of two types immunomodulators based on their effects: immunosuppressants and immunostimulators.
Stress reduces the overall performance of broilers alterations in body homeostasis results in physiological changes of an individual causing stress. Various kinds of stressors can induce stress, among which, heat stress plays a major role. The heat stressed birds may fall short to perform with respect to the body weight, feed efficiency, laying performance and mortality. However, the heat stress susceptibility of a breed depends upon various factors such as strain, feathering pattern, nutritional plane and production system. Further, it can be considered as a factor responsible for immune suppression in birds, resulting in infectious diseases and reduced performance in the flock. This causes potential economic losses and the farmer need to face the debts in the business. So, to counteract this stress induce immune suppression, one should follow certain strategies including supplementation of some nutrients like vitamins, minerals, electrolytes and some additives like probiotics, prebiotics, essential oils, polyherbal preparations, aspirin, betaine, and acetic acid. These substances bring about the change in the internal environment of gastrointestinal tract.
Avian Immune System——–
The avian immune system consists of two types of immune mechanisms – nonspecific and specific.
Nonspecific Immune Mechanisms
Non-specific immune mechanisms consist of natural ways with which a bird tries to resist a disease. These natural mechanisms need to be given special attention while designing a good health management program:
• Genetic factors. Continuous selection programs over generations help breeders to develop chickens that have high resistance power against certain disease organisms. As an example, some strains of chickens are genetically resistant to the lymphoid leukosis virus.
• Body temperature. Chickens have a high body temperature, which ranges between 40.5°C – 41.5°C/105°F–107°F. This prevents a number of common mammalian disease organisms from affecting them. For example, black leg disease and anthrax of cattle are not problems in poultry.
• Anatomic features. A chicken’s skin is covered with feathers. This prevents it from external injuries. Pathogens are unable to penetrate the chicken’s intact body coverings (skin and mucous membranes), becoming trapped in the body’s mucus secretions.
• Commensal bacteria. The gut of a healthy chicken has a stable microbial population. These microflorae help prevent disease organisms from invading and establishing themselves.
• Cilia in the respiratory tract. The trachea is lined with cilia. Cilia play an important role in removing disease-causing organisms and debris. While cilia can help in removing mild levels of dust, high levels of dust or ammonia can make the ciliary system to become overwhelmed and ineffective.
These non-specific mechanisms clearly indicate the importance of biosecurity and good farm management to keep chicken healthy and productive.
Specific Immune Mechanisms———-
This is an acquired immune system, which has two components — non-cellular (humoral) and cellular components. The non-cellular component includes immunoglobulins (or antibodies) and the cells that produce them. Antibodies are specific to the foreign materials (antigens) to which they attach. For example, the antibody against Newcastle disease virus attaches only to the Newcastle virus, not to the infectious bronchitis virus. The cellular component of the specific immune mechanism includes all the cells that react with specificity to antigens, except those associated with antibody production. The cells associated with this system, T Lymphocytes (T-cells), begin as the same stem cells as B-Lymphocytes (B-cells). T-cells are programmed in the thymus, whereas B-cells mature in the bursa of Fabricius.
Immunity Types
There are two types of immunity – active immunity and passive immunity. Active immunity is defined as the process in which a chicken produces its own antibodies following exposure to a foreign body such as bacteria. This process occurs when the chicken is given a vaccine or when there is field disease challenge. Active immunity is adversely affected by anything that damages the cellular or humoral immune systems.
Passive immunity (maternal immunity) is the process wherein the chick receives pre-made antibodies from a hen through the egg. Maternal antibodies are present in the yolk, albumen, and fluids of the egg.
Poultry Gut Immunity
The gastrointestinal tract is an important organ for maintaining health. It has two important functions -– to absorb nutrient and to act as the barrier against unwanted compounds and germs. Because of its extensive surface, the GI tract is also a major port of entry for many pathogens. The GI tract immune system has the major responsibility to act on known pathogens while ignoring components of food or “commensal” microorganisms that inhabit the gut. Failure to do this might end in intestinal inflammation and tissue degeneration.
Inflammation
The immune system in the intestines plays a major role in maintaining gut health. The inflammation due to compromised gut health if not tightly controlled can cause great damage to the intestine itself. It poses risks to high producing poultry such as broilers that include growth retardation, increased risk of infections, etc. Clostridia, like infections, benefit from this type of inflammation. One possible option to reduce the inflammation is to reduce the energy content, and thereby decrease the inflammatory stimulus. A few AGPs were found to have anti-inflammatory action. As there is a great awareness today to reduce AGPs and/or completely withdraw AGPs altogether, producers are actively searching for suitable alternatives.10
Immune modulators
An immunomodulator may be defined as any biological or synthetic substance that can stimulate/suppress either innate, adaptive, or both arms of the immune system. A potent immunomodulator has many advantages over antimicrobials. Because immunomodulators do not affect microbes directly, they may avoid the problem of rapid emergence of resistance
Causes of heat stress
In our country, the high ambient temperature is a big concern, as in summer, the temperature may reach up to 40-47°C. The temperature above 35°C induces heat stress on birds. The second reason is an increase in relative humidity above 60% along with high temperature. It causes heat load on birds due to lack of heat dissipation by birds. Third reason can be taken as the low protein intake by birds. Although proteins increase the heat production, but the low protein diets may cause detrimental effects, as they will reduce feed efficiency and body weight. It will also increase feed consumption and abnormal fat deposition. Another reason is the concentration of ammonia in the shed, which will result in accumulation of aerial ammonia in shed which may increase by high temperature and can affect the homeostasis in birds. Hence ideal and balanced feed with all essential nutrients should be brought into practice.
What is immunosuppression
Immune suppression literally means, “suppression of the immunity”. It is a great concern in the poultry industry worldwide. It may occur due to infections, but, stress (high temperature, poor nutrition, poor management) induced immune-suppression is reported already by many researchers. depressed immunitydue to cortisone production and leucopenia due to atrophy of lymphoid organs such as thymus, bursa of fabricius, and spleen. It results in poor performance, low body eight, increased FCR, mortality and secondary bacterial infections in the flock.So, to counteract the above consequences due to immunocompetance, we must look into certain strategies for its amelioration by means of immunomodulation or immunopotentiation through dietary interventions and medications.
Commonly used immune modulators in poultry
Direct-Fed Microbials (DFMs) / Probiotics
DFMs have been used as prophylactic agents against enteric pathogens, presumably by balancing microbiota, by modulating host immunity, or both. The dietary B. subtilis, when used in a Broiler as a potential growth promoter, can provide beneficial effects on Broiler performance and modulate host humoral and cellular immune responses to enteric pathogens.7
DFMs stimulate the immune system that is exhibited in higher production of immunoglobulins, stimulation of macrophages and lymphocytes activity and also by augmentation of the production of γ-interferon.1 Regular and judicious use of probiotics has a striking effect on the immune system viz. stimulation of both humoral and cell mediated immunity through enhanced production of natural interferons/cytokines; increased macrophage, lymphocyte and natural killer (NK) cell activity; up regulated oxidative burst in heterophils; and increased immunoglobulin (IgG, IgM and IgA). Probiotics produce a gut-stabilising effect and good immune regulation, particularly through balanced control of pro-inflammatory and anti-inflammatory cytokines. Feeding probiotics could improve antibody titres against viral diseases like Newcastle disease (ND) and Infectious bursal disease (IBD). The use of probiotics increases the amount of IgA found in the intestinal lumen, the numbers of IgA, IgM and IgG producing cells, as well as the number of T cells in the cecal tonsils.5
Butyrate
Butyrate has been appreciated for its beneficial effects on the host, including trophic and anti-inflammatory effects on epithelial cells.11 A scientific study indicated that dietary butyrate supplementation can improve the growth performance in chickens under stress, and that this could be used to moderate the immune response and reduce tissue damage. It also found butyrate supplementation in the diet of broilers to be beneficial, especially in the presence of immune stress. Improvement of growth performance in poultry may be achieved, in part, through modulation of the response to immune challenge with butyrate administration.
Essential Oils
Essential oils exert their mode of action mainly with their bactericidal effects of essential oils. Production and secretion of endogenous digestive enzymes, modulation of the immune system, and antifungal and antiviral activity have been proposed to address their effects on animal performance. Carvacrol, a commonly used essential oil in animals, has anti-inflammatory properties.
Prebiotics
Prebiotics are non-digestible feed ingredients that are metabolized by specific members of intestinal microbiota and provide health benefits for the host. Prebiotics are capable of modulating gut microbiota and the immune interactions in favour of chicken health.
Nutritional strategies
At high environmental temperature, feed intake is reduced, which may cause deficiency of micronutrients like vitamins and minerals. Vitamin A, E and C have major role in stress alleviation and immunomodulation in heat-stressed chicken.
Vitamin A
Vitamin A is a fat soluble vitamin having significant role in immune function and reproduction. In layer if supplemented @ 8000 IU/Kg. diet, it reduces heat stress and increases egg production. While in broilers, it’s supplemented @ 15000 IU/Kg. diet, which gives excellent results with improved weight gain, feed efficiency and carcass quality. It is very effective if given in combination with zinc to minimize heat stress.
Vitamin C
Ascorbic acid is a water soluble vitamin and can be synthesized in poultry and not required as a supplement under normal condition. However, in heat stressed chicken, it is proven to be beneficial by reducing corticosterone production with simultaneous increase in insulin and thyroid levels. It also deprives protein derived glucose synthesis and increase fat degradation. In case of broiler breeders, it increases egg weight, fertility and hatchability. In heat stressed broilers, ascorbic acid requirement is more, as it also acts as antioxidant. It improves carcass yield and quality, feed efficiency, carcass protein content and reduces crude fat.
Vitamin E
Vitamin E is a fat soluble vitamin and its dietary intake reduces heat stress and improves egg production. It increases yolk and albumen contentin the egg. It increases plasma concentration of yolk lipids by production and release from liver. It protects the liver and body cells from oxidative injuries also. Vitamin E supplementation @ 250 mg /Kg. diet is beneficial for egg production at high temperature. Vitamin E shall be supplemented before, during and after any stressful condition.
Herbal plants and HSPs
Natural herbal plants and their derivatives like secondary metabolites are being used traditionally for their therapeutic and immunomodulatory functions. These herbal principles or metabolites include saponins, glyacoproteins, polysaccharides, and flavonoids etc. These metabolites have a wide variety of medicinal values actions like lymphocyte stimulation etc. Aloe vera,&Agelicagiggas are some of the examples of these herbs. Beside this some Chinese herbs like Panax ginseng, Gingiberofficinale, and Saussurealappacan be quoted as good examples of such herbs.Many of the herbs mentioned above are used as the immunomodulators, tonics and adaptogens.
Essential oils
Essential oils (turpenes and phenylpropenes) are the derivatives of mixture of aromatic oily liquids obtained from the leaves, flowers, buds, wood, bark, fruits, seeds, of some plants. They have their own characteristic odor or fragrance. Some of them are liquid at the room temperature while some are volatile in nature. The mixture of different essential oils containing cavacrol, thymol, terpenoids, garlic oil, cineol, geranitol, â-inone, citral, graniol etc, when added @ 24mg/Kg of diet, acts in a wide range like antioxidant, antibacterial, antimycotic, antiparasitic, insecticide, hypolipidemic factor, immune-modulator, digestive stimulator and heat stress alleviator.They are potent antioxidants and acts as preservative by its antioxidant properties along with the meat obtained from the birds fed on such feed which is fortified with essential oils and improves their shelf life. Turmeric powder, if included in poultry rations @ 0.1-0.2% will enhance the immunity of the birds. Essential oils from tulsi, ashwagandha, garlic, turmeric and aamla have found to be beneficial in summer season to reduce heat stress in layers. Aamla and ashwagandha are also helpful in broilers with respect the body weight, immune status and as an antioxidant.
Probiotics
Probiotic is a generic term and its products containing bacteria and/or yeast cultures that stimulates the growth of microbes capable of modifying gastrointestinal environment to favor health and improving feed efficiency. Probiotics mainly contain Lactobacillus species like L. bulgaricus, L. acidophilus, L. lactis, L. plantarum, S. thermophilusetc, and some other species like Enterococcus fecalis, and Bifidobacteriumetc, which enhance health by producing lactic acid in gut and making alterations in gut microflora and eliminating pathogens to improve feed utilization.It also develops immune response by stimulating immune cells to produce cytokines. Probiotics, especially lactobacilli, could modulate systemic antibody response to antigens in chicken, when fed @ 50 mg/Kg. diet. Lactobacillus based probiotics also enhances the response against coccidiosis, especially against E. acervulina. These probiotics also stimulate cells of cecal tonsils.
Minerals and others:
Chromium, anessential trace mineral for normal physiology of birds improves feed efficiency, feed intake, body weight and carcass characteristics if supplemented @120ppb/Kg of diet. It functions for deprivation of serum cortisol and insulin levels. Chromium usually depletes stress in heat stressed birds, and hence its supplementation in diet is very necessary. Organic form of chromium is more active in biological system than that of inorganic one. Cr-Nano particles are more effective than Cr-Macroparticles as having greater absorption rate in the gut. Chromium also increases antibody response and leucocytes activity. Following are the recommended levels of inclusion of above said feed supplements and additives. Conclusion: Preferences for optimum production performance with high feed efficiency under various climatic conditions have made modern chicken more prone to heat stress and subsequent immunesuppression. Certain nutritional strategies like inclusion of feed supplements such as vitamins, minerals and electrolytes were proven to be very beneficial in challenging immune-suppression. Some novel feed additives like polyherbal preparations, essential oil mixtures, probiotics, acetic acid, betaine, aspirin, and prebiotics also have made it advantageous to alleviate heat stress and to potentiate immunity of chicken and are proven to be very promising in enhancing heat tolerance of birds.
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