Every time I say to people " You should vaccinate your flock against...a...b...c...," I get the same reply: I Never vaccinate, I believe birds should handle their own immunity.
I belong to a show poultry organisation called SASPO in South Africa, the South African Show Poultry Organisation. In short it is an organisation that monitors pure bred poultry in SA, and ensures the continuity of these pure breeds, by strict adherence to standards. We have shows for this purpose.
Unfortunately, putting a bird on a show that lasts (here at least) five days, plus the transport that is really long distance in Africa, place your bird in a stress situation among 3000 odd other birds and lock them up for five days, it is a recipe for disaster.
Caging is often inadequate here, birds often get cold as all shows are in winter, summer being too unbearably hot.
So: I vaccinate.
Firstly because it is the law here to vaccinate a flock against endemic diseases such as Newcastle and Infectious Bronchitis, and Gumboro.
So those are a must. There are so many types of Newcastle, I only do two strains: The first is a mild vaccine that sensitises the bird to the stronger strain given five days later. The Infectious Bronchitis is included in both vaccines.
the I vaccinate against Gumboro, (IBD), pox at 6 weeks and MG, Mycoplasma Gallisepticum, which is an underlying disease that creeps up on you without warning. if you see a flock of birds growing at uneven pace, with some not thriving while others grow by leaps and bounds, chances are you have MG. MG is shed by infected birds in times of stress. It will re surface any time there is stress, stress being inclement weather heat or cold, overcrowding, bullying in the flock, predators, rats, lack of food, wrong feed, lack of water or lack of access to food and water if there is overcrowding.
Obviously you try to minimise stress but this is not always possible.
These vaccines are essential though there are others that you could add, like Infectious Coryza. In some countries, I know in some states of the US it is illegal to vaccinate against some diseases such as Infectious Laryngotracheitis, IL, as the vaccinated birds do become carriers. There are vaccines available now, called ML Modified laryngotracheitis which is I believe milder and does not cause a vaccine positive.
Vaccinating is a choice. You need to find out what diseases are prevalent in your area, and vaccinate accordingly. If you have had a flock of birds for many years and have religiously vaccinated along the way, you can cut down on some vaccines, or even miss a generation with no ill effect.
It is wise after five years of regular vaccination to cut back, and allow the natural immunity of the bird to assert itself. You could perhaps cut out the Coryza, or Mareks. I no longer vaccinate against Mareks, although I did for many years, because it is no longer a problem in my flock. Should I suspect a problem, Mareks will feature in my vaccination programme once more.
The immunity of your birds lies in many things:
1. the environment. What feed they get, the housing, cleanliness of the bedding, overcrowding.
2. Vaccination programme.
3. Handling. deworming, delousing, general health of feathers.
I firmly believe that NOT immunising your flock is playing russian roulette, even if you only have 20 birds. remember no one is an island, and you will have people around you with birds. There are air borne diseases that can affect everyone in your area up to a 10km radius.
We cannot control avian influenza, or the bad poultry practices of other people, but we can make a difference in our own back yard by being vigilant and consistent in our caring for our own birds.