Integrated Disease Prevention Management in Poultry
Mr. Reddy, N.K. Praharaj, S.V. Rama Rao and B.L.N. Reddy
Various aspects of poultry health maintenance and disease prevention are outlined. The present day health problems are often multi factorial and require special attention to avoid disastrous consequences. Health is a state of complete physical, mental and social well being of poultry, which is an important factor determining the profitability of poultry production. Disease represents a restraint to reproductive potential and yield, feed conversion efficiency and product quality. The causative factors of disease are classified as agent, host and environment. The interaction of these three factors is required to start disease in birds. Intensive health monitoring of elite primary breeders, GGPs, GPs is essential for effective prevention of vertically transmitted diseases. Integrated disease prevention and control involves all the measures designed to prevent or reduce the incidence, prevalence and consequences of the disease. Broadly these measures include 1. Controlling the reservoir or source of infection. 2. Breaking the routes of transmission and 3. Manipulating the susceptible host. The practical use of vaccines to prevent or reduce disease losses in poultry is discussed. The objectives of vaccination, the types of vaccine, vaccination programme, combined vaccines and vaccination failures are presented in a non technical manner.
The concept of preventive medicine in poultry is now more important than ever, because the occurrence of disease will limit the performance of the bird and prevent it from achieving its maximum genetic potential. The present day poultry health problems are seldom unifactorial, on the contrary. They are very often multi factorial, requiring special attend on to avert disastrous consequences. These problems, which may not be frank disease hut results in sub and time consuming to overcome. It is much better to avoid those happenings in the first place through an integrated system of health maintenance and disease prevention. Successful prevention depends on knowledge of causation, dynamics of transmission, identification of risk factors and flocks at risk, availability of prophylactic or early detection and treatment measures, application of these measures to appropriate or flock and continuous evaluation procedures applied.
Structure of poultry industry and disease control
The basic structure of the poultry industry can be regarded as a Breeding Pyramid. The apex of the pyramid is occupied by Elite (Primary) Breeders, Great Grand Parents (GGPs) and Grand Parents (GPs), followed by Parents in the middle and commercials at the bottom of the pyramid (Hunton, 1993).The major genetic manipulations take place at elite and GGPs level.This involves careful recording of the main production parameters and also, selection for desired traints. At this level intensive health monitoring is essential, so that diseases which can be vertically transmitted or which can depress performance are excluded. At this stage, the pathogens detrimental to the production and health of birds are to be eradicated from the elite breeders to GGPs, GPs and Parents can produce devastating results in the commercial poultry industry as hundreds or thousands of commercial birds are descended from each bird of the elite breeder flocks. So the disease status, immune system and genotype of elite flocks have potentially profound effect on the health of commercial flocks. The need to protect elite and GGPs from catastrophic and vertically transmitted diseases dictates high levels of biosecurity.
Concept of health and disease
Health is one of the most important factors determining profitability of all systems of poultry production. It is defined as a state of being that is not merely absence of disease, but a state of complete physical, mental and social well being of poultry. Health and disease lie along a continuum and there is no single cut-off point. The lowest point on the heath disease spectrum is death and the highest point corresponds to perfect health. It is thus obvious that health fluctuates within a range of optimum well being to various levels of dysfunction, including the state of total dysfunction, i.e. death.
Health and Disease Spectrum
1. Perfect Health
2. Better Health
3. Freedom from Disease
4. Unrecognized Disease
5. Mild Disease
6. Severe Disease
Health status not only influences the average performance of a flock but also its variability. The perfect health implies that a bird should be able to express as completely as possible the potentialities of its genetic heritage. This is possible only when a bird is allowed to live is healthy relationship with its environment an environment that transforms genetic potentialities into phenotypic realities.
The disease is Just the opposite of health i.e., any deviation from normal functioning or state of complete physical or mental wellbeing. The term "disease" literally means "without ease" (uneasiness)disease, the opposite of ease when something is wrong with body function. Disease represents a restraint to reproductive potential and yield, feed conversion efficiency and product quality.
The causative factors of disease may be classified as Agent (Pathogen), Host (Bird) and Environment ( Jordan , 1996). These three factors are referred to epidemiological triad. The mere presence of agent, host and favorable environmental factors is not sufficient to start the disease in bird. What is required is an interaction of these three factors to initiate disease process in the bird. The agent, host and environment operating in combination, determines not only the onset of disease which may range from a single case to epidemics but also the distribution of disease in the flock.
A. Agent factors
1 . Biologic agents: The biologic agent may include viruses, Chlamydia, rickettdiae, mycophasmas, bacteria, fungi and parasites, These agents exhibit certain biological properties viz., a. Antigenic variation, b Variation En virulence, c. Variation in immunogenic, d. Infectivity (numbers necessary to establish infection in the host), e. Tropism, f. Survival within and outside the host and g. Resistance/Susceptibility to antimicrobial and disinfectants.
2. Nutritional agents 3- Physical agents 4. Chemical agents 5. Mechanicalagents
B. Host Factors (Intrinsic)
3. Immune status
4. Stress (associated with point of lay or social stress)
C. Environment factors (Extrinsic)
b) Ambient Temperature
2. Air Quality
b) Gases like NHs, C02. And CH4
c) Free radicals
a) Floor/Cage rearing
b) All-in-all out
c) Multiple ages
d) Vaccination & Medication
e) Debarking, Dubbing & Sexing
h) Hygiene and disinfection
i) Disposal of dead birds, litter and hatchery waste.
a) Deficiency or excess of nutrients
b) Water quality and supply
c) Feed toxins
d) Feed contaminants
e) Change of diet
f) Drugs-antimicrobials, growth promoters
c) Wild birds
d) Opportunistic infectious agents
a) Population density
b) Sex ratio
D isease transmission
Infectious diseases do not occur by chance. It is required for a harmful infection environment. The disease causing organisms are introduced or transmitted to a poultry flock in a variety of ways.
Disease prevention and control
Disease control involves all the measures designed to prevent or reduce the incidence, prevalence and consequences of the disease. The basic approach in controlling disease is to identify the weak points of diseases and break the weakest links in the chain of transmission (Pattison, 1993). Broadly these measures include: 1) controlling the reservoir or source of infection, 2) breaking the routes.
1) Controlling the reservoirs and source of infection
If the first link in the chain of causation (i.e. the disease agent) is deemed to be the weakest fink, logically, the most desirable control measure would be to eliminate the reservoir source. This includes all the measures directed to reduce the quantity of the agent available for dissemination.
1. Early identification of reservoir/ source of infection
2. Treatment of affected birds
3. Epidemiological investigation
4. Isolation (separation) of infected birds from healthy birds
5. Serological testing and removal of carriers
6. Hygienic disposal of dead birds, litter and hatchery waste
7. through cleaning, washing and disinfection of farm houses, equipment
8. Feed and Water quality control
9. Hygienic hatching of chicks
2) Breaking transmission routes
A major aspect of communicable disease control relates to "breaking the chain of transmission". Microbes travel from place to place by chicken crates, egg filler flats, trucks, other equipment and people. They can be transmitted from one flock to the other through workers. The organisms are found on the skin and in the digestive and respiratory organs of dogs, cats, rats, mice and wild free flying birds, Flies, beetles and other insects are also notorious spreaders of disease causing organisms. Blocking the routes of transmission imply on control of environmental factors, that is, to bring about an adjusted equilibrium between host and environment through encouraging some ecological influences and inhibiting others (Woodger.1996).
3) Manipulating the susceptible host (birds at risk)
The third link in the chain of transmission is the susceptible host or birds at risk. One effective way of controlling the spread of infection is to strengthen the host defense (Cheville, 1979). Under certain circumstances this may be accomplished by the following ways:
1. Genetic improvement of disease resistance by conventional selection and genetic engineering (gene, transfer).
2. Manipulation of immune system by
b) Avoiding social, environmental and managerial stress.
c) Providing good quality, well balanced feed
Over decades of research, avian immune system has been successfully manipulated to benefit the poultry industry. The efficient functioning of avian immune system is judged through successful vaccination programme. It is one of the most powerful and cost effective weapons of poultry preventive medicine. Diseases with both demonstrated and predicted potential for producing disastrous losses have been controlled through vaccination. Vaccination is the second line of defense against disease losses, and it keeps disease losses within acceptable limits when sanitary management fails. Vaccination has to be designed according to the needs of the situation (Beard, 1979).
1) Vaccination objectives: The first key to develop an effective vaccination programme is to determine the vaccination objectives. The most important objectives of vaccination in poultry are as follows:
1. To prevent or reduce disease losses due to morbidity or mortality in vaccinates.
2. To prevent spread of diseases
3. To provide parental antibodies to chicks of immunized hens
4. To prevent adverse effects of vertically transmitted diseases in chicks
5. To prevent diseases which infect young chicks and subsequently results into development of unprofitable adults?
6. To protect against disease which damage immune system?
7. To reduce condemnation at slaughter
8. To prevent or reduce losses due to poor egg quality
2) Types of vaccines: Once the objectives are established and decision is made to pursue the vaccination programme, the type of vaccine, frequency/timing and route of administration should be matched to those objectives. Vaccines for poultry are of two types, either live or killed, each having specific advantages or uses.
Live vaccines contain a virus or bacteria that must infect the chicken and multiply in its body to produce immunity, hope fully with minimal reaction. Advantages of live vaccines are ease of administration, low price, rapid onset of immunity and a broader scope of protection, since chickens are exposed to all stages of the replication virus.
Killed vaccine is prepared from bacteria or virus which have been inactivated and processed. Killed vaccines are usually combined with adjuvant such as aluminum hydroxide or oil. Adjuvant enhance the immune response by increasing the stability of vaccine in the body which stimulates the immune system for a longer period of time. Advantages of Rifled vaccines are assurance of administration of a uniform dose, safety, development of uniform levels of immunity and increased product stability.
3) Vaccination programme: Vaccination programme vary with the type of poultry and severity of the field challenge.
The immune responses needed in broilers are for a short duration because of the short life span of the bird (six weeks). Breeders and layers require different programme because of longer life span (Aini, 1980). When designing a vaccination programme, one must first determine the disease challenges faced by the poultry industry in the region. To be effective, a vaccination challenge should be provided before any natural exposure to infection.