Chickens Don't Get Colds
This is an important point and I've seen it brought up in a lot of places but it's worth repeating. Chickens aren't mammals, they don't get the little colds that we do. If I wake up with a sneeze, I barely notice it. I've probably got a little cold or my allergies are acting up. Sure, chickens can sneeze if things are dusty or there's a lot of ammonia, but that's not the same as a cold.
Chickens don't get colds. They get viruses. Viruses are interesting little beasties in that you don't fight them directly. If you put your bird on an antibiotic because they're sneezing, you're only dealing with any secondary infections that might pop up and/or masking symptoms. The virus is not affected, your bird is still sick with the virus. Even after the virus has run it's course, the bird may be a 'carrier'. This means they still have the virus, they're just not showing any symptoms. They can pass this virus on to birds that don't have it yet. This carrier state can go on for a couple months or the rest of the bird's life, depending on the type of infection.
Consult a vet if you have birds in your flock starting to sneeze/cough/sound congested or if there appears to be something else spreading. What they have needs to be identified.
What Chickens Do Get
There are a host of things that your chickens can get. Many are very contagious, some are deadly, and some just won't go away. It's a reality that some of the diseases that chickens can get are not curable, treatable, and result in the flock being culled and everything being sterilized in an attempt to keep the infection from spreading to any new birds you acquire. Some are even reportable to the state. My reference of choice is Merck's Veterinary Manual.
Merck's Veterinary Manual - Poultry
I'm not going to list all of the diseases here, but the ones you hear about most often are:
Infectious Bronchitis, abbreviated IB
Mycoplasmosis (mycoplasma gallisepticum and mycoplasma synoviae), abbreviated MG and MS respectively
Fowl Pox, also seen as chicken pox
Infectious Laryngotracheitis, abbreviated ILT
The reality is that a lot of these disease are out there. Marek's is assumed present in most large flocks (Merck Veterinary Manual, 2013). MG and MS is found in a lot of flocks in the US. The only way to be certain whether or not a bird has any of these is a blood test that can help identify carriers. Necropsy can also be used to give a definitive diagnosis in birds that are acutely ill. Many of these diseases start out the same, particularly the respiratory ones.
One way to keep these diseases at bay is to have a solid biosecurity plan for your healthy flock. This is a good article on biosecurity:
American Bantam Association - Recommended Biosecurity for Non-Commercial Flocks
Keep in mind that even a closed flock can be exposed to some things. Some of the infections can be carried by wild birds or can be transmitted from an infected flock via dander. Some can lay dormant in the soil. Unless you have your birds completely secured inside with no contact with the ground and no contact with wild birds, there is some chance of transmission. Your vet can help you weigh the risks. Immunity can be gained through exposure, but you can also have carriers in your flock that are just asymptomatic. Reoccurring 'colds' can be a virus that reappears under times of stress.
Vaccinations and Chickens
And back to the original point of this article. With the number of contagious viruses running around, it's not a surprise that there have been vaccines developed to prevent them. For the commercial flocks, these are part of how they manage thousands of birds without having regular outbreaks. For exhibitors that introduce their birds to strange poultry and stress, it's a way to avoid some infections. For a backyard keeper with a closed flock, they're used less often.
Many hatcheries offer vaccinations against Marek's and coccidosis for their one day old chicks. This is because the vaccination needs to be done within the first day of life to be effective. As Marek's is a devastating virus in a flock, I recommend it. It's cheaper to have the hatchery do it and something you don't have to worry about. Coccidosis is handled through medicated feed or the vaccination. As I don't like to use medicated feed (organic producers can't use medicated feed, but can vaccinate), I have my birds vaccinated for this as well. Many do not have these vaccinations done, but it's not a risk I'm willing to take. Infectious bronchitis, bursal (if it's active in your area), and Newcastle can also be vaccinated against in that first week.
For broilers, that's pretty much it. They are only around for 12 weeks on average. For your layers, exhibition birds, and pets, there are other possibilities. Fowl pox (if it's active in your area), coryza, and MG all have vaccines available. This is an example of what a commercial layer's vaccination program could look like:
Merck's Veterinary Manual - Vaccination Programs
Your Chickens and Vaccination
What does all of this mean for you and your chickens?
Vaccination of your chickens is a personal choice and there's no one size fits all. The diseases I would see in New Hampshire aren't the same as the ones you'd see in New Mexico. Some keepers don't vaccinate at all, some keep to a rigorous schedule of boosters. Neither is right or wrong. There is the argument that keepers should breed for disease resistant birds, but at the same time, subclinical infections can affect productivity without showing symptoms (Marek's Disease, Merck Veterinary Manual, 2013). Without checking to see if the bird is a carrier, there is no way to be certain whether the bird is resistant or is asymptomatic.
If you're concerned about your flock and want advice on potentially vaccinating, the first step would be to contact your state vet and see what diseases are active in your area and see what they recommend for your type of flock. They will be able to give you advice based on your region and your individual situation.
APA - Directory of State Vets
APA - State University Poultry Departments
Vaccinations can get expensive. The vaccines are sold in doses of 1,000 and once open need to be used immediately. That is a lot of waste. Some of the vaccines are inexpensive, such as IB and Newcastle, while the corzya vaccine can rack up $100. If for nothing more than economic reasons, a shotgun approach to vaccination is probably not the best plan for the non-commercial flock. Some vaccinations, such as bursal, are only for use if you're in an affected area. Other vaccinations may require a prescription.
In my case, working with my extension office and local keepers, I'm going in the direction of Marek's, Newcastle, coccidosis, and IB as diseases I want to vaccinate against. They are in my area and my birds are likely to encounter it, since my flock is not closed and they free range in an area with a big wild bird population. I have decided that these are the diseases that I will specifically arm them to face, understanding that other immunities and exposures will probably occur during their lives.
If you do decide to vaccinate, be aware of the kind of vaccine used. Live vaccine can make your birds mildly sick and can put your birds into a 'carrier' state temporarily. Do not mix birds that have not been vaccinated with birds that were recently vaccinated with a live vaccine. I learned that one myself and that was actually the trigger of my research. Quarantine doesn't identify carriers, as they show no symptoms but are shedding the virus. Most shows won't allow you to exhibit a bird that has received a live vaccine 30 or 45 days before the show since they could pass that along to other birds at the show. Also, if you are showing a bird, be sure to schedule a blood test as required by your state and the show rules. Don't put this one off, or you might miss your show!
I wish there was a clear cut bit of advice I could give for this topic, but unfortunately it's too complicated for that. My only real advice is to talk to your state vet and fellow keepers in the area, get a good biosecurity plan together, get your birds from a reputable source, quarantine, be aware of who could be a carrier (exposure and live vaccine), and don't think that your flock sneezing just means that there's a cold going around. Chickens don't get colds.
Chickens, Vaccines, and You
This is a hot button topic for a lot of people, so I'm not looking to give advice. I'm looking to make people aware of something that's a reality...