Chicken Health

Contents

Introduction
Basic Hygiene
Isolate sick chickens
Disinfect your hands
Disinfect areas
       Three basic concentrations to use
       Maintenance Hygiene
Immunity
       Importance of Natural Immunity
       Farm Immunity
       Immunity and Mortality in Start-up Chicken Operations
       Herd Immunity
       Acquired Immunity
       Maternal Immunity
       Immunity in Show Poultry
Non-responders
A Basic Vaccination Program
Why is Mortality in Chickens so high?
Viral Diseases

Introduction

With the exception of Broilers, we do not advocate the stringent Bio-security measures normal in large commercial enterprises which strive to maintain pathogen free environments. Such measures are expensive and in the long term prevents the establishment of natural immunity, which is the small-scale poultry keeper's most effective weapon against disease.

Broilers are not recommended for small farmers. They are better suited to large concerns and mass-production. Very few small farmers have ever made a long-term profit from rearing and/or selling broilers. Certainly we have not met one.

However, some basic measures are essential to avoid unnecessary disease and mortality:

Basic Hygiene

• As soon as possible, established a closed group. In other words, having to bring in chickens from outside sources is always a risk
• This means you should aim to breed your own chickens
• Avoid bringing in chickens that you do not know the source of
• Never bring in vaccinated chickens

Isolate sick chickens

• Sick chickens not only infect others, recovery is often dependent of the total virus onslaught. The more sick chickens together, the higher the virus concentration.
• Disinfect your hands when handling sick chickens, spray some Hibitane® or any of the sanitizers prescribed for Corona on your hands before and after. Rub your hands together until they are dry. Hibitane® is obtainable in concentrate and must be diluted in water, preferably in a spray bottle.
• As soon as possible, established a closed group. In other words, having to bring in chickens from outside sources is always a risk.
• This means you should aim to breed your own chickens
• Avoid bringing in chickens that you do not know the source of
• Never bring in chickens that have not been vaccinated

Disinfect your hands

• When handling sick chickens, spray some Hibitane® or any of the sanitizers prescribed for Corona on your hands before and after handling the chicken.
• Rub your hands together until they are dry.

 

Hibitane® is obtainable in concentrate and must be diluted, preferably in a spray bottle. The active ingredient in Hibitane® is Chlorhexidine. A number of products containing this compound can be obtained from Dischem.

Disinfect areas 

• When clearing a cage of chickens, disinfect the coup with Virkon S, which is available in concentrated from (50g & 10kg quantities).
• Don’t use F10! In spite of what the distributors claim, there is significant evidence exist that there are viruses (eg. Canine Parvo Virus) that this product does not kill.
• Dilute in a spray bottle or rucksack spray and disinfect all surfaces.
• See the enclosed directions which concentrations to use for different applications.

 

Three basic concentrations to use

• Mild – 1 teaspoon per litre
• Concentrated – 2 teaspoons per litre,
• Oral – 1 teaspoon per 10 litre that can be used in drinking water.

 

Maintenance Hygiene

• Spray Vircon S mild solution
• over all chickens once per week
• Over sick chickens once per day

• Spray Vircon S Concentrated Solution over all concrete paths once per week
• Vircon S oral solution in water once per month

 

Immunity

Immunity in essence results from antibodies that develop in the body of an animal after exposure to an antigen (a foreign body) which may or may not be harmful. A harmful antigen is referred to as a pathogen. Viruses and bacteria are examples of potentially harmful pathogens that may result in disease. Exposure to such pathogens usually results in the formation of antibodies that may protect against the disease that the animal was exposed to.

An antibody is specific to the pathogen that resulted in its formation or a pathogen very similar thereto. The sketch above is a basic illustration of antibodies that developed in response to a New Castle Disease infection as well as antibodies that developed in response to a Infectious Bronchitis challenge. Antibodies that developed in response to New Castle Disease will not protect again antibodies that developed against Infectious Bronchitis and vice versa. This is because the viruses are very different. 

If antibodies develop faster than the virus, the virus will be destroyed. If the virus replicates faster than anybodies can develop, the animal will die.

Various different types of immunity can be defined. The following are relevant to the small scale chicken farmer:

• Natural Immunity – The immunity in a population developed over generations through natural exposure to disease

• Farm Immunity - Immunity that develop on a particular farm in response to specific pathogens on that farm
• Herd Immunity - when 80% or more of a population have developed immunity against a specific pathogen.
• Acquired Immunity – Immunity in an animal that developed in response to vaccinations
• Maternal Immunity – Passive immunity derived from the mother via the egg

 

Importance of Natural Immunity

• The feeding of the poor depends on the availability of poultry that are naturally immune
• In general poor people in South Africa do not have refrigeration facilities and cannot realistically buy frozen chicken that will quickly decay
• This segment of our population have no real alternative other than to buy live chickens that they can take home and keep alive until required for food. In this scenario natural immunity is vitally important
• Poor people are generally not in a position to vaccinate their poultry
Content for id "farm" Goes Here

 

Farm Immunity

Most small-scale chicken farmers practice little or no bio-security. If you visit them, they will often invite you into their chicken coups with little though that you may be carrying disease. The up-shot of this is that over time the operation will develop a high natural immunity in their flock.

However, the immunity that develops may be specific to that farm. I the chickens from this farm went elsewhere, their immunity may not cover than against disease that were not prevalent on the home farm. This is what is referred to as "Farm Immunity".

Immunity and Mortality in Start-up Chicken Operations

An new start-up operation on premises that have not had chickens for a long time, at least for two years, may well be free of disease, at least for a while. However, sooner or later disease will creep in, no matter how efficient the bio-security may be. When this happens, mortality may initially be high until herd immunity develops. Once this happens, disease will will decline to manageable proportions. In chicken operations, a mortality of between 10 and 15% is normal.

Natural or Farm immunity cannot develop in the total absence of disease. Therefore, as difficult as it may be, some disease on small-scale chicken farm may in fact be desirable. It should just be kept to manageable levels.

Herd Immunity

Herd Immunity is when more than 80% of a population has developed immunity against a particular disease. If a virus should enter the population, there is thus an 80% chance that the virus will attempt to infect an immune individual, in which case it will be destroyed by the antibodies of that individual.

Should one of the 20% susceptible individuals be infected, there will still be 80% of the population that cannot be infected and the virus is unlikely to spread in the population. At the very least the spread will be slow and the virus concentration will remain relatively low in comparison to a population where 100% of the individuals were susceptible. In this scenario even the susceptible individuals will stand a greater chance of recovery.

Acquired Immunity

Acquired Immunity is an immunity in an animal that has developed in response to a one or more vaccinations.

In what can be described as the first documented vaccination, a British physician Edward Jenner in 1796 infected an eight year old boy with Cowpox, a virus relatively harmless to humans, which resulted in the boy becoming immune to Small Pox, a virus disease deadly to humans. The Cowpox virus is sufficiently similar to the Small Pox virus to enable the antibodies that developed in response to to the Cowpox virus exposure to also protect against Small Pox.

On a basic level, vaccination is the deliberate exposing of an animal to a harmless form of the disease, thereby causing the development of immunity against the more serious form of that disease.

In modern medicine this is usually a synthetically produced virus that is close to the natural form but harmless; close enough so that the antibodies produced in response to the vaccine will be close enough to the natural antibodies to recognise the serious disease virus and destroy it before the chicken becomes sick.

Maternal Immunity

Newly hatched chicks, like mammals and humans (humans are mammals!), are initially protected against disease through antibodies derived from their mothers. In mammals this transfer of immunity is via the colostrum in the milk in the first few days after birth and in chickens the transfer of immunity is via the eggs. This type of immunity is what is referred to as Maternal Immunity.

This maternally derived immunity is passive and declines after hatching. How quickly this happens depends on the level of immunity of the mother against a particular disease. A high level of Maternal Immunity takes longer to decline than a lower level. The Maternal Immunity needs to be "boosted" before it declines to a level at which a chick becomes susceptible to infection.

This "boosting" can happen through exposure to the disease itself, which can be very risky, or by vaccination. The level of immunity of the mother depends on the mother's exposure to a particular disease:

• either the disease itself or
• through vaccination

 

Unfortunately a high Maternal Immunity can "protect" a chick against a vaccination, causing that vaccination to be ineffective. To overcome this problem, chicks need to be vaccinated a few times against a particular disease. Eventually the Maternal Immunity will decline to a level at which the vaccination will not be destroyed and the immune system of the chick will respond.

Immunity in Show Poultry

If you show your poultry, you will have no option but to expose them to other poultry from all over the country. In addition, you will expose them to members of the public who come to view an exhibition with absolutely zero control over who may have come from a diseased flock or not.

You will also have no control over whether other exhibitors vaccinate their chickens or not; or how ineffective their vaccination regimes may be. It also often happens that sick chickens sometimes arrive at shows. This is not necessary that they left home sick, but often the stress of traveling may cause them to become sick.

Therefore, the only conclusion that can be reached is that natural immunity levels within exhibition poultry is high. That said, responsible exhibitors will practice a proper vaccination regime. Not only to protect their own poultry, but also that of their fellow exhibitors.

Non-responders

It is important to note that vaccination is not always successful. This is a normal phenomenon. Some individuals will not respond to vaccination at all while other individuals will to build immunity to varying degrees. Some will develop a high immunity and others a barely sufficient immunity.

The level actual level of immunity that develops can depend on a lot of factors. Vaccination procedures are important to the success of a vaccination will be discussed in detail below.

A Basic Vaccination Program

1- Day-old: NCD* (a strain suitable for day-old chicks) + Infectious Bronchitis

2-Weeks old: same as one-day old

4-Weeks-old: NCD* (La Sota Strain) + Infectious Bronchitis

Every 8 weeks: NCD* (La Sota Strain) + Infectious Bronchitis

September & December every year: Fowl Pox

Gamboro: Breeder females only, once per year

* NCD = New Castle Disease

Why is Mortality in Chickens so high?

 

In chicken operations, a mortality of between 10 and 15% is considered acceptable. The phenomenon is best explained by the somewhat controversial Ecological theory of the r&K Continuum as illustrated above. While there are exceptions, a surprising number of species adhere hereto in terms of their Life History Strategies.

Insect can reproduce in their millions with a life expectancy of sometimes just a few days. Elephants for example, have a life expectancy of around 65 years, a gestation period of 22 months and a high survival rate. A reproductive rate of not more than about one offspring every 3 to 9 years from about 14 to 17 years of age. A total of not more than about 12 calves in a reproductive life.

Humans have a lower natural life expectancy than elephants, about 45 years. However, medical science has extended life expectancy to well beyond that of elephants. The human gestation period is 9 months with generally have only 1 offspring per year during the reproductive period between 12 and 40 years of age. In total up to 15 children are possible in a reproductive life-time.

A bitch can have an average of 9 puppies per year in a reproductive live span of about 6 years. Therefore about 50 puppies in a reproductive live. Life expectancy is around 12 years.

A hen can lay up to 300 eggs in her reproductive year, and with a hatching rate of about 75%, can have as many as 200 offspring. Hence a lower lifespan and a higher mortality.

Viral Diseases

• There is no cure for viral diseases other than the animal's own immune system killing the virus through the production of antibodies
• The only way for us to protect our birds against virus infections is by vaccination
• Natural immunity will also protect a bird, but they need to be exposed to the disease in the first place; and this can be costly due to potentially high initial mortality
• Antibiotics only cure secondary bacterial infections and not the virus infection

There are many virus diseases that affect poultry. A few common ones most likely to impact on the small-scale chicken farmer in South Africa will be described here.