Nutritional modulation to enhance immunity in chickens

Prevention is better than cure, as they say. Many nutrients, energy, amino acids, vitamins and minerals - play different but significant roles in the immune response and so can contribute to keeping birds in good health, without the need for medication.

Presently, the aim of commercial poultry breeding is to achieve higher body weight and maximum egg production per unit of feed intake. However, there is a negative correlation between production and immunity in chickens as a result of the conflict between production and immunity, i.e. maturation and function oh the immune system. Accomodation of all the physiological demands within the limited resources, i.e. nutrients, available to birds may be the factor responsible for the negative relationship between performance traits and immunity. The genotypes with the maximum bodyweight exhibit lower immunity, as indicated by E. coli lesion score and cellular immunity antibody titres, compared to those having lower body weights. Therefore, the possibility of breakdown of the immune system in commercial chicken crosses is more evident nowadays than before.

In addition to genetic selection, certain non-genetic factors like dietary nutrient concentration also modulate the expression of the genes responsible for immuno-responsiveness by altering the maturity of the immune system and magnitude of antibody production.

Defence mechanism in chickens

Under intensive farming conditions, the poultry environtment contains ubiquitous micro-organisms that continuously challenge the bird;s immune system. Generally, the invading pathogen will be attacked by antibodies, whichs wil neyutralise, weaken and inactiveate the pathogen and finally, phagocytic cels will engulf the invader. The mechanism is quite effective in controlling extra-cellular phatogens, such as bacteria. For the intracellular pathogens-viruses-cell-medicated immunity (CMI) plays a key role. The CMI protects the host by destroying the cells that harbour the pathogen with the help of cytotoxic T-lymphocytes. Againts invading pathogens, the immune system produces a variety of compounds like acute phase protein (APP), proteolytic and hydrolytic enzymes, oxygen radicals and nitrogen derivatives, which destroy the invader or infective cells.

Nutrient recommendations are typically developed using indices of productivity such as growth, egg production and feed efficiency. The criteria for adequacy of immunocompetence are often ignored. Nutrients also influence the maturity of the immune system and magnitude of the antibody. During the acute phase of the immune response, the greatest nutritional need is for the synthesis and release of APP by the liver. The process requires more energy and amino acids than are normally needed for responding leucocytes. Interactions among various nutrients and imbalace or toxicity of nutrients lead to disturbances in normal physiology of the bird, with consequent immunosuppresiaon in chickens.

Energy

Variations on concentration of energy in the diet modulate the immune response in birds, probably due to the change in intake of nutrients, wich influence the immunity. Energy intake regulates the acitvity of the immune cells and activity of certain hormones, e.g. thyroxin, corticosteroids, growth hormones, glucagons, catecholamines, wich influence immunity. Variation in the level and composition of dietary fat also influence the immune response in chickens by altering the structure of the cell membrane and modulating the synthesis of prostaglandins. Mortality associated with E. coli and Mycobacterium tuberculosis was reduced by increasing the level of fat from 3% to 9% of the diet. Antibody titre against sheep red blood cells (SRBC) antigen was markedly increased with supplemental tallow at 6% in the chick diet. Higher levels of unsaturated fatty acids enhance immune function by stimulating macrophages.

Protein

The growth of bursa and thymus are relatively faster than the bird’s body growth. Therefore, it is important to supply the required quantity of protein, particularly during the early growth phase. Deficiency of protein at this stage leads to the improper development of lymphoid organs. Several research workers have suggested that there is a higher amino acid requirement for immunity than for growth. However, the influence of level of protein in diet on severity of disease depends on the type of infective organism. The lesion score to E. coli  inoculation dcreased with the increase in the protein level (18, 20.5 and 23%) in broiler diets. With coccidiosis, the mortality decreased from 32% to 8% in chickens fed protein-deficient diets compared to those fed a normal protein level.

High dietary protein increases the activity of trypsin in the chicken gut. A high level of trypsin in the gut leads to a faster release of coccidia from oocysts, which will aggravate the disease symptoms.

Dieatary methionine levels in exces of those required for maximum growth are essential for maximising immunity. Methionine is required by the thymus-derived- T-cell function. Methionine deficiency produces severe lymphocyte depletion and atrhopy of the bursa and an increased suspectibility to Newcastle disease coccidiosis.

Cystine supplementation also stimulates cellular and humoral immunity (70 to 84% as effective as methionine)

Deficiency (16 to 50%) of branched-chain amino acids, i.e. isoleucine, leucine, and valine, reduces the antibody titres againts SRBC in broilers.

Immunoglobulins contain a high concentration of valine and threonine. A deficiency of either of these amino acids reduces the immune response in chickens. A higher ratio between leucine to valine + isoleucine reduces immunity due to structural antagonism between the three amino acids. The absorption of valine and isoleucine are inhibited by a high leucine content din the diet.

Increasing the dietary concentration of lysine improved the haemagglutination and agglutinin titres, and IgG and IgM levels.

Arginine is a substrate in the synthesis of nitric oxide, a cytotoxic product that is helpfu in phagcytic activity of macrophages and kills bacteria and intracelluar parasites.

Vitamins

Vitamins act as co-factors in several metabolic functions in immune reactions and therefore, deficiencies  of vitamins cause impairmentt of immunity. Generally, higher levels of vitamins than the current recommendations will increase the immune response.

Retinal

This vitamins Is important for maintaining the cellularity of the lymphoid organs and epithelial tissues and for enhancing both cellular and humoral immunity. Vitamin A helps in maintaining the mucous membrane of natural orifices in healthy condition to prevent the invasion of microorganisms. Vitamin A directs differentiation and development of B-lymphocytes. The concentration of vitamin A in the diet modulates the expression of retinoic acid receptors on lymphocytes in chickens.

The production of immunosuppressive agents (hydrocortisones) is reduced with higher levels of vitamin A in the diet. Furthermore, deficiency of vitamin A causes keratinisation of basal cells of the bursa and impairment on the response of T-lymphocytes. Therefore, deficiency of vitamin A impairs immunity by producing defective T, B-lymphocytes, impaired phagocytosis and reduced resistance to infection. Increased morbidity due to Newcastle disease virus has been reported due to a deficiency of vitamin A in the diet. The requirement of vitamin A for maximum immunity, i.e. lymphoid organ weight, was higher than for the bodyweight gain in the chicken. An increase in vitamin A from 12850IU to 42850 or 74045IU/kg decreased mortality due to E. coli, and CRD in chickens and increased the rate of clearance of the pathogen from the blood. However, the benficial effect of higher levels of vitamin A depends on the concentration of other fat-soluble vitamins in the diet. An excessive level of vitamin A interferes with the utilisation of vitamins D and E.

The administration of 60IU of vitamin A per chick per day during a severe attack of coccidiosis reduced mortality from 100% to almost zero. However, practical chick and young layer diets should contain 4000 and 2000UI/kg, respectively. To minimize stress damage and also to prevent immune suppresion, dietary vitamin A levels shoul be increased to ten tomes the normal requirement. A combination of vitamin A (14000IU/kg) and zinc (65mg/kg) has been shown to enhance growth and both humoral and CMI immunity in chickens.

TO BE CONTINUE……

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Sanitation: Cleaning and Disinfectants

Diseases and infections have always been a big problem for the poultry industry - especially in the hatchery. Fortunately, microbial contamination can be prevented and controlled through good management practices and modern products for health care.
Microorganisms are everywhere! Some of them are relatively harmless, others are highly pathogenic. Some of them are deadly threat to the species, while remaining harmless to other species. Some organisms are easily destroyed, while others are very difficult to remove. The moral is: Treat all microorganisms as a serious threat to living young.
The understanding of the terms used to describe microbial control is important in selecting appropriate measures to eliminate pathogenic organisms. Three terms are often used, but often poor sterilization, disinfection and sanitation.

• Sterilization - The destruction of all infective and reproductive forms of all microorganisms (bacteria, fungi, virus, etc.).
• Disinfection - The destruction of all vegetative forms of microorganisms. Spores are not destroyed.
• Sanitation - The reduction of pathogenic organism numbers to a level at which they do not pose a disease threat to their host.

Most hatchery personnel have the impression that they are approaching a sterile condition because they use disinfectants when "disinfecting" the facilities. In fact, they may only achieve a sanitized condition at the very best. The most important consideration to remember when striving for a sanitized hatchery is that cleanliness is essential.

Proper cleaning of facilities removes the vast majority of all organisms and must be used before application of disinfectants. This applies to all areas within the hatchery including floors, walls, setters, hatchers, trays, chick processing equipment, air and personnel. The success of a hatchery sanitation program is limited only by its weakest link.

It is extremely important to remove as much organic matter as practicable from surfaces to be disinfected. All debris including down, egg shells, droppings, tissue residues, etc. must be removed from the hatchery. This is followed by thorough cleaning using warm water and appropriate cleaning aides. Care is focused on selecting the proper detergent and thus producing the cleanest hatchery environment possible. Special attention is placed on compensating for variations in hardness, salinity and pH of the cleaning water. A thorough rinsing with abundant quantities of clean sanitized water completes the cleaning process and removes most lingering residues of detergents, organic matter or microbial organisms that can interfere with the effectiveness of a disinfectant.

Only after the facilities have been thoroughly cleaned are the surfaces treated with an appropriate disinfectant solution. Not all disinfectants are suited for every situation. When selecting the right disinfectant, carefully consider:

1. The type of surface being treated.
2. The cleanliness of the surface.
3. The type of organisms being treated.
4. The durability of the equipment/surface material.
5. Time limitations on treatment duration.
6. Residual activity requirements.

If the surface is free of organic matter and residual activity is not required, quaternary ammonium compounds and possibly halogen compounds can be used effectively. However, if surfaces are difficult to clean, residual activity is required or the contaminating organisms are difficult to destroy, then multiple phenolics or coal tar distillates may be needed.

Careful attention must assure that the disinfectant, if used as directed, meets requirements of the user. Be reasonable and don't expect the product to produce unattainable performance. Instead, select a different product or modify disease control practices.

In general, disinfectants can be divided into seven major categories. A more detailed summary of the basic attributes of each category of disinfectants is available later in this discussion as "General Characteristics of Disinfectants". The various classes of disinfectants are:

1. Alcohols
2. Halogens
3. Quaternary Ammonium Compounds
4. Phenolics
5. Coal Tar Distillates
6. Aldehydes
7. Oxidizing Agents

Although many disinfectants are available, those most suited for use in today's hatcheries include quaternary ammonium compounds, phenolics and aldehydes. However, each disinfectant is used only in appropriate locations for meeting the purposes for which it is designed.

Several considerations must be remembered when using any disinfectant to maximize its effectiveness. Some of these general considerations are:

Few disinfectants are effective instantaneously. Each requires a certain amount of time to bond with the microbe and exert a destructive influence. Allow adequate contact time (usually 30 minutes is sufficient) or select a different disinfectant.

When selecting disinfectants, consider their effectiveness on organisms that are of greatest concern. If a hatchery is experiencing problems with a certain viral disease, the disinfectant selected must be effective for destroying the specific organism causing the problem. Not all disinfectants are effective on all types or species of organisms.

In most situations it is advisable to clean and disinfect in two different operations that are separated with thorough water rinsing. Many cleaning/disinfecting producers promote their product based on ease and economy of use because they clean and disinfect in one operation. If these products are used, make sure that they satisfy all efficacy requirements demanded of other disinfectants.

The efficacy of disinfectant solutions is usually enhanced when applied in warm solutions rather that cold solutions. "Hot" solutions, however, may reduce disinfectant efficacy or promote a "cooked-on" condition for unremoved protein-rich residues.

When possible, allow all surfaces to dry thoroughly prior to reuse. Dryness helps prevent the reproduction, spread and transport of disease organisms. Although a surface is clean, it is more easily recontaminated with organisms if water remains on the surface.

A listing of important characteristics for the more commonly used disinfectants used by the poultry industry is shown in General Characteristics of Disinfectants.

It is important when selecting the best disinfectant to consider its effect upon the developing embryo and the hatchery environment. Embryos are in a very sensitive stage of development when the eggs enter the hatchery. They can be severely affected if subjected to chemical vapors, even if a sterile environment is provided.

It must be remembered that an egg is not produced in a sterile environment. Before it is laid, the egg is subjected to a series of microbial attacks that can reduce the embryo's potential to develop into a healthy, robust chick. The vent of the hen is probably the most contaminated area that an egg passes through. Poorly maintained nests can also distribute organisms to noninfected eggs. Fortunately, nature has provided several protective barriers for the embryo. Hatchery personnel must not conduct any procedure that interferes with the egg's natural defense. Producers must make every effort to collect and store eggs so that natural protections are not compromised.

Keeping egg shell surfaces dry is very important to prevent excessive microbial contamination and shell penetration. Without benefit of aqueous water the potentially dangerous microorganisms have little opportunity to invade the egg shell and infect the embryo. Sweating of eggs as they are moved from warm to cool environments must be prevented if sanitation programs are to be successful.

Embryos have the same requirements prior to pipping that the chicks have following hatching. They have the need for heat, moisture, and a high-quality source of air. They can be severely affected by harmful fumes originating from many chemicals often found in or near the hatchery. Although hatchability may not be affected, the quality of the chicks can be reduced. Whenever unusual odors from detrimental chemicals are detected in the hatchery, the product must be removed. This applies to all chemicals within the hatchery, including disinfectants. As an example, vapors produced by improper use of phenolic disinfectants can cause changes in egg proteins and impair hatchability and chick quality.

Improper selection or use of some disinfectants can damage or hinder the function of hatchery equipment. Many disinfectants are corrosive and damaging to equipment parts. Some disinfectants can clog and gum-up spray nozzles if added to the water used in humidifiers. It is possible that electronic control devices can also be severely damaged or destroyed after prolonged exposure to some disinfectants.

Select disinfectants wisely and always follow label directions for their safe use. Not only does management have the responsibility to maximize hatchability and chick quality, but also to provide a safe working environment for the hatchery personnel. Safety of the people working in the hatchery must never be sacrificed for cost or productive efficiency.

Assuming that a proper state of sanitation is achieved, it must be remembered that the status of disease-free surfaces can be compromised if facilities are not maintained properly. Hatchery personnel must be made aware that they can be a major source of reinfection by transporting of microorganisms on clothes, hands and attire. Since people are direct carriers of microbes, provisions must be made available at appropriate locations in the hatchery for the washing of hands and footwear. Laboratory coats and caps can significantly reduce the spread of microbial organisms. Restricting movement of hatchery personnel by assigning duties within specific areas can reduce the distribution of organisms throughout the hatchery.

The risk posed by disease causing organisms is a constant challenge to hatchery personnel. Always use control measures that have been proved effective rather than trusting visual cleanliness as an indicator of sanitation. A clean surface does not always indicate a disease-free state. Assuming so may be fatal to the chicks and the management program.

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