Mycoplasma – The Chronic Recurring Disease – Chronic Respiratory Disease (CRD)


Mycoplasma refers to a family (also known as a genus) of bacteria that lack a cell wall. This means that common antibiotics such as penicillin, or other cell wall synthesis (the combination of several entities to form something different (such as the process by which amino acids form proteins, or proteins form an organelle)) targeting antibiotics (also known as beta-lactam antibiotics). They can be parasitic (living off other organisms) or saprotrophic (living off dead or decomposing matter).

Mycoplasma in Chickens

The most common type of mycoplasma affecting chickens is mycoplasma gallisepticum. This type of mycoplasma is parasitic, and affects chickens, wild birds, turkeys, pigeons and other fowl. It is the causative agent of chronic respiratory disease (CRD) in chickens and infectious sinusitis in game birds, turkeys, pigeons etcetera. It is transmitted either through the eggs of carrier hens, or by chicken to chicken (airborne) transmission. It is highly contagious and is spread rapidly when the birds sneeze.

Some breeders breed without the knowledge that their flock is infected, therefore passing the disease on. Stress is thought to lower the resistance to the mycoplasma bacteria, and the disease sets in and the birds begin to exhibit symptoms. Some people dismiss this as the ‘common cold’, or think its ‘nothing’ and the disease is allowed to run riot throughout the stock.


  • Sniffling
  • Sneezing
  • Rasping or rattling in the throat
  • Foamy eyes and nose
  • Yawning

More advanced symptoms include:

  • Loud, sharp ”Coughing” noise
  • Stiffness
  • Stretching legs and wings, sometimes trailing them
  • Difficulty balancing, sometimes even falling over


Diagnosis is generally based on symptoms, and a blood test at the vets will give definite results. A course of medication will follow. Tylan is recommended for this purpose, but it is only available on prescription.

Some people recommend Tylan injections rather than tylan oral, as this is faster and usually more efficient.


A  vaccination is now available. The F-Strain is a low pathogenicity strain which gives immunity to the  birds for the laying season, but leaves them as carriers. It is, however, fully virulent for turkeys. Recently, 6/85 and ts-11 were introduced. These two live nonpathogenic strains give immunity, without making the inoculated bird a carrier.

Can You Breed From Birds With Mycoplasma?

Can You breed from chickens with Mycoplasma? Please comment below on how you feel about breeding from chickens with this chronic illness.

Well, the long and short of it is that there is no easy answer. If you have birds with mycoplasma, and you want to breed from them, every situation must be treated as a different case!

It all depends on how, where, when and why the birds have been infected, as well as the intensity of the infection.

Also, some strains are more virulent than others, so this will also have some effect on the decision to breed or not to do so. It should also be taken into account, that once the birds are heavily infected, there are two ways of transmission. One of these occurs when the birds are stressed, and actively ”shedding” pathogens. This is when the disease is carried from bird to bird through the air. The other is when the bird is not exhibiting symptoms, but still carrying the disease. This is when the bird transits the disease through the egg!

Birds which have been exposed to the disease, but have not contracted any signs are the obvious ones to breed from, if any. That said, they may still be carriers, but that could (theoretically at least) actually make the chicks immune to the disease! Because, as I discussed in my article on the chicken’s immune system (not yet published at the time of going to press), if an adult bird has immunity to a disease, some antibodies are actually passed on to the chick! But, it is a double edged sword, because, at the same time, disease pathogens could have been passed on, and this leaves the chick open to disease.

Birds that have been treated for mycoplasma have obviously had the disease more severely, so chances are, the oviducts would have been infected, guaranteeing the chicks to come down with the disease, UNLESS you medicate the birds with tylan, or similar, and collect the eggs that you will use for hatching  during this period of medication. IF you are lucky, the tylan may have intercepted pathogen transmission to the egg, or in some mysterious way, avoided infection!

Obviously, placing eggs under an infected hen is NOT advised, because she will only infect them, even if the eggs were uninfected! Therefore, an incubator is a better answer. An uninfected hen is not advisable either, unless she is vaccinated with a non-pathogenic strain, because if the eggs were NOT pathogen free, they will infect the previously uninfected hen!

So, can you breed from chickens with Mycoplasma? Yes. Yes you can, BUT you need to look at EVERY SINGLE CASE seperately, and evaluate  the risks and benefits, because, at the end of the day, it’s not really worth taking the risks of breeding from infected birds, unless you are trying to rescue a breed on the edge of extinction!!!