vaccination in poultry industry

Introduction

Disease prevention through vaccination is one of the aspects of bio-security. Disease causing organisms can be classified as smallest to largest - viruses, mycoplasma, bacteria, fungi, protozoa and parasites. All these organisms are susceptible to chemotherapy, except viruses. Bacterial infections are controlled through antibiotics but not much medication is available to fight viral infections thus vaccines are used. Control of viral diseases is dependent on prevention through sanitation and bio-security and by vaccination. Vaccination is no substitute for effective management. Vaccine is effective in reducing clinical disease but exposed birds may still get infected and shed disease organisms. Vaccination before infection occurs in a flock is the best means of protection.

Vaccines are intended to stimulate the immune mechanism of an animal to produce antibodies, which will inactivate pathogens and also produce minimal harm. Vaccine is a protective measure against outbreak of contagious and infectious diseases and plays a major role in preserving productive health of poultry.

Vaccine contain specific biological substances called antigens (Ag).In the bird antigen is recognized as a foreign body and responds by producing specific antibodies (Ab). An ideal virus vaccine is made from a non disease producing highly immunogenic virus causing little reaction and much protection. Vaccine may be live or killed, both types give reaction. (A bacterial vaccine is live or inactivated preparations of bacteria termed bacterins).

Live vaccine:

Live vaccine consists of live micro agents. Live vaccines are viruses or bacteria weakened under controlled laboratory conditions into a safe virus/bacteria strain that can infect the chicken immunity and stimulate immunity without causing severe disease. Live vaccines stimulate the complete immune system including local, cellular and humoral immunity. Protection following vaccination is relatively rapid (few days to a week) depending on properties of particular virus/bacteria. Protection for most of live vaccines does not last for a full breeder cycle and needs regular revaccination.

Live vaccine can be administered by mass applications such as drinking water, spray or aerosol. Live virus vaccines reproduce in the host to increase their number. Most poultry vaccines are a live virus type. They can be given at a younger age than killed vaccine.

Killed or inactivated vaccine:

Killed or inactivated vaccines contain pathogens that have been chemically inactivated with or without a suitable adjuvant so that they will produce immunity, but are unable to cause or transmit the disease. They are killed in such a manner that the part of the organism which injures the bird and allows the pathogen to multiply is destroyed, leaving the immunity stimulating portion of the pathogen intact. The adjuvant causes a mild reaction at injection site attracting cells such as macrophages, which start the immune response. Adjuvant also acts as a slow release formulation stimulating the immune system for extended period of time. Inactivated vaccines do not stimulate complete immune system like live vaccine. They do not induce local immunity and only limited cellular immunity but there is a very strong humoral response (circulating antibodies) and takes up to 6 weeks for this protection to develop. A killed virus product is dependent on the number of antigenic units (virus particles) present in the vaccine dose to stimulate antibody production.

Inactivated vaccine must be administered by injection to each individual bird at the prescribed dose rate is laborious.

Development of competent vaccines is one of the factors for emergence of poultry industry.

Vaccination schedule aids in achieving maximum benefits through maximum protection of flock against disease. Under optimal standards of management & husbandry practices, with no exposure to pathogen a bird is sure to respond effectively to vaccination. In addition to providing all the nutrients through feed, strict bio-security rules following vaccination schedule is must. Small decline in any of the managemental practices can lead to irreversible loss, in form of disease outbreak.

Parent flock is vaccinated in such a way that there are required levels of antibodies of major diseases in chickens. The yolk sac antibody protects the chicks from natural infection but is maintained till defensive organs (thymus, bursa, spleen & bone marrow) are fully functional (21 days of age). Vaccination schedule based on the parent flock vaccinations with slight variation based on season or prevalence of disease in area is helpful.

More doses or higher frequency of vaccine does not have any effect on protection of bird. Only required amount of antigen is utilized to induce the immune system to produce antibodies, additional dosage is either eliminated or deposited hindrance the immune system in recognizing other antigens- immune-suppression develops leading to vaccine failure. Additional quantity/dosage leads to excess expenditure too.

POINTS TO BE CONSIDERED TO AVOID THEIR INTERFERENCE DURING VACCINATION ARE:

1. High level of passive immunity:

Primary protection comes from immunity passed on by hen to her chicks called maternal immunity and is passive. Maternal antibodies may neutralize vaccine in young chickens, if given at too early stage. When the maternal antibodies disappear the chick is left unprotected, even though it has been vaccinated. Thus it is better to administer the vaccine when the passive immunity is low after about 5 to 7 days.

2. Stress:

Anything which upset physiological and psychological stability of bird is a stressor and reaction of an individual to the stressor is called stress. Stress leads to severe immune-suppression which may result in failure of vaccination. Vaccinate birds only under stress free condition.

3. Inactivation of live vaccine & Spilling of vaccine:

Improper handling during transportation, storage, and at time of administration may lead to failure of vaccines. Vaccine contamination must also be prevented as it can cause serious complications. Live vaccines should always be stored and transported at 2-8oC and never exposed to sunrays. The diluents should be chilled before the reconstitution of vaccines. Live vaccines are disease agents which can cause disease under certain circumstances. If vaccine dribble out it may become a source of disease in birds, thus tip out or left over vaccine must be neutralized with strong disinfectant and empty vials or droppers/containers for be burnt or disinfected to prevent accidental spread to other poultry.

4. Health Status of birds:

Immune system of a sick bird is weak and cannot satisfactorily withstand a vaccine. Vaccination of sick bird can precipitate the incidence of disease and it can also lead to other diseases. Sick birds should therefore, be allowed to recover before vaccination. Immunosuppressive disease cause immune-suppression in birds and the birds will not respond properly to the vaccine resulting in vaccine failure

5. Temperature & Ventilation:

Ambient temperature above 30oC affects the immune system of the birds adversely, so vaccinate birds during cooler period of the day only. Ammonia is produced as breakdown of uric acid (an end product of protein metabolism). Improper ventilation leads to higher concentration of ammonia (NH3) in poultry house due to which there is immune-suppression and failure of vaccination. This ammonia is prevented to accumulate in the poultry house by ensuring proper ventilation.

6. Age, dose and route of vaccine:

Route and dose prescribed by the manufacturer must be followed. Under dosing will not protect the bird adequately. The age of bird at vaccination, proper timing of revaccination affects the level, quality and duration of immunity. Vaccines may be administered:

a) Parentally:
Parental routes are:
Subcutaneous
Intramuscular
Intranasal
Intraocular
b) Orally The vaccine is given orally through drinking water. Following precautions should be taken for proper oral vaccination in birds:
Stop the water supply to the birds for one hour before vaccination in hot weather and two hours in cool weather.
Use plain water without any water sanitizer for mixing the vaccine.
Skimmed milk powder should be mixed in water before adding the vaccine to it. It should be mixed @ 3g/Lit of water. This prevents the microbicidal activity of the residual sanitizer and also it stabilizes the microbial antigens. The vaccine should be mixed in such a quantity of water as will be consumed by bird within one hour.
Follow the instructions from the manufacturer.

CARE DURING VACCINATION PROGRAMME:

Buy the vaccine from a reliable well recognized source after checking the expiry of vaccine, as they have limited lifespan within which they must be used.
Vaccines should be stored at a temperature of 2^o to 8^o degree C. They should neither be frozen in a freezer nor stored above 8^o C. Same temperature is to be maintained during transporting; a flask with ice cubes or iced water is also suitable for the purpose. In farm storage in lower compartment of refrigerator is suitable.
Vaccination should be carried out during the cooler period of the day which reduces stress in birds. Temperature above 30^oC may affect vaccine potency. Mixing of vaccine should not be done in sun, as direct rays will affect the potency and inactivated vaccines. Vaccine should be mixed and kept in shade during distribution period. Don´t use premixed vaccines kept overnight.
As vaccines are vacuum sealed (administered via drinking water) when opened in air draw contaminated air into the container thus such vaccines must be opened under water into which it is to be mixed.
Tape water is mixed with chlorine to kill germs and this water when used can kill inactivated live vaccine. All sanitizers in water should be avoided during vaccination, thus avoid such water or treat before use. Antibiotic treatment should be stopped three days before and after vaccination. Live virus vaccine are readily destroyed by sanitizers and chlorine. Water equipments should be free of disinfectant.
For vaccination via drinking water, the amount of water for mixing varies with age, type of bird and climate. Water should be withdrawn 2-3 hours before giving the vaccine for fast consumption of vaccine. Remove water up to 2 hours in hot weather and 2-4 hours in cool weather before administration. All vaccines should be consumed within two hours of mixing; adding skim milk powder prolongs vaccine life. Adequate dosage of vaccine must be provided to flock. As water is withdrawn all birds will come to drink water so it is advisable to distribute the vaccine in more drinkers than needed for normal watering of flock.
Designing and implementing an effective vaccination schedule requires a thorough knowledge of disease, risk situation in a specific area, an understanding about the interaction between chick and vaccine and thorough planning. Decide whether or not to vaccinate against a disease depends on the likelihood that the birds in a flock may be exposed to that specific disease.
As a good breeder hen produces a maximum number of hatching eggs thus there must be least negative impact of disease on egg production. Broiler chicken also relies on breeder hen for maternally derived antibody during first few weeks of life for protection against disease. Thus breeder vaccination needs additional attention. For many viral diseases the breeder is primed with live vaccine followed by an inactivated booster vaccination 4-6 weeks later to provide protection for full production cycle.

GUIDELINE FOR SUCCESSFUL VACCINATION:

Vaccination of poultry younger than 10 days (5-7days) of age cannot be expected to produce uniform or lasting immunity, even in the absence of maternal immunity. Exception is that vaccination for Mareks disease is ordinarily given on the day of hatch.

Guideline for vaccine administration:

Each vaccine is designed for a specific route of administration so use only the recommended route.
Do not vaccinate sick birds (except in outbreak of laryngotracheitis or fowl pox).
Protect vaccines from heat and direct sunlight.
Most vaccines are living, disease producing agents so handle them with care.

Layer Breeder

Bulk of breeder vaccinations are administered in the first 18 weeks (rearing phase)Protection should be at peak level when first hatching eggs are collected and persist up to end of egg production cycle.

To avoid stress to the breeder bird vaccination during lay is kept to an absolute minimum, generally limited to the mass administration of certain live vaccines (ND- Newcastle disease, IB-Infectious bronchitis).

Vaccination at day old or in ovo with suitable MD-Markes Disease vaccine to reduce losses, Sensitive nature of vaccine used requires specific attention to vaccine handling and administration procedures. Vaccination in hatchery is preferred. Even the best MD vaccination does not equate guaranteed freedom.

Vaccine against coccidiosis has been a routine addition to most breeder vaccination schedules. Administered correctly these vaccines induce a predictable immunity to the selected Eimeria strains.

Broiler Breeder

Vaccination of the broiler breeder does not end at protecting the hen and egg production. Breeders immunity has a direct impact on the immunity of the broiler at hatch. Protection to offspring´s/chicks is transferred via yolk called maternally derived antibody (MDA). Chicks hatched in an environment will face the same disease challenges the hen faced in past, but there is balance now a day by keeping hen in one environment, hatching eggs in hatchery and raising broiler chick in different environment away from breeder.

IBD-Infectious Bursal Disease is best example of vaccination in breeders primarily for benefit of broiler.IBD specific MDA protects the broiler from infection during the first two to 3 weeks, after which live IBD vaccines are administered.

Vaccination of the breeder prevents transmission of reovirus via egg and transfers protective levels of reovirus specific MDA to broiler chick. Reovirus is associated with poor growth in broilers.

Avian encephalomyelitis (AE) and chicken infectious anaemia (CIAV) are both viral pathogens transferred `from breeder to broiler via the egg.

Breeders are vaccinated against salmonella and are less susceptible to salmonella infection; there is also reduced risk of salmonella transmission via the egg. The protection level of MDA transferred from breeder to the broiler protect against infection during 1st weeks post hatch, when broiler is most susceptible to infection

TABLE: 1. VACCINATION SCHEDULE FOR POULTRY (BROILER)