What is CRD ?

CRD is an abbreviation commonly used for Chronic Respiratory Disease.  The term CRD is mostly identified with Mycoplasma gallisepticum, or MG for short.

In the poultry world there are many respiratory diseases. Many of these respiratory diseases share the same symptoms, and are only identifiable through lab testing by blood sampling or PCR testing. The following are all respiratory diseases: Fowl Pox, Newcastle disease, Infectious bronchitis (IB), Avian influenza (AI), Infectious coryza, Laryngotracheitis (LT), Turkey rhinotracheitis, Swollen head syndrome (SHS), Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS), and Mycoplasma meleagridis (MM)

Mycoplasma gallisepticum ... defined

There are many thoughts about the prevalence, treatment, management and irradication of MG.

MG has always posed a great threat to the commercial industry, both meat birds and layers. 

Mycoplasma gallisepticum is minute in size with minimal genetic information and with a total lack of a bacterial cell wall.


Infection with Mycoplasma gallisepticum occurs naturally in chickens and turkeys. Transmission occurs by two major routes.

~vertically through the egg (1-2% occurrence ; 6-9 weeks after outbreak as high as 50%)

~horizontally by direct or indirect contact of susceptible birds with infected carriers or contaminated debris.

The route of infection is via the conjunctiva or upper respiratory tract with an incubation period of 6-10 days. Transmission may be transovarian, or by direct contact with birds, exudates, aerosols, airborne dust and feathers, and to a lesser extent fomites. Spread is slow between houses and pens suggesting that aerosols are not normally a major route of transmission. Fomites appear to be a significant factor in transmission between farms. Recovered birds remain infected for life; subsequent stress may cause recurrence of disease. 

It is important to differentiate from Infectious Coryza, Aspergillosis, viral respiratory diseases, vitamin A deficiency, and other Mycoplasma infections such as M. synoviaeand M. meleagridis (turkeys).


Tilmicosin, tylosin, spiramycin, tetracyclines, fluoroquinolones. Effort should be made to reduce dust and secondary infections.


Eradication of this infection has been the central objective of official poultry health programs in most countries, therefore M.g. infection status is important for trade in birds, hatching eggs and chicks. These programs are based on purchase of uninfected chicks, all-in/all-out production, biosecurity, and routine serological monitoring. In some circumstances preventative medication of known infected flocks may be of benefit.

Shared waterers, feeders, dander, poultry shows (where birds are handled one after another), hair (up to 3 days), clothing, shoes, standing water (up to 9 days), poultry swaps, vehicle tires are all ways this bacteria can be spread. 

External Signs/symptoms


~runny nasal discharge

~watery or foamy eyes

~poor productivity

~stunted or slowed growth

~poor appetite

~leg problems

~reduced hatchability and chick viabilty

For an overview as well as a checklist for poultry diseases and their symptoms. 


Why do I need to know about this?

We want all poultry enthusiasts to know about this disease and to have an understanding of its prevalence. We also hope to provide you with good information as to how to help keep your flock clean, what are your options when you discover this is in your flock. We also hope to be a support for those that have gone through the devastating experience of eradicating an entire flock due to the discovery of MG. 

At one time MG was so prevalent in the commercial industry that work began to study and eradicate it from the industry as it was costing great financial loss.Those efforts resulted in scientists using a treatment for the eggs to eradicate MG from the developing embryo. As the scientists were successful in treating these eggs and developing MG free stock this began the eradication of MG in the commercial industry.  Many commercial breeder flocks of layers and meat birds today are of clean stock and are monitored by the USDA and the NPIP program. 

None of the "well known" big hatcheries that sell exhibition poultry take part in the MG testing program. 

Backyard poultry, poultry exhibitors, and small farm flock owners are under   Subpart E—Special Provisions for Hobbyist and Exhibition Waterfowl, Exhibition Poultry, and Game Bird Breeding Flocks and Products with the USDA NPIP program.  MG testing is a voluntary program under subpart E.

MG is worlwide in distribution. There are many theories on how many poultry flocks (under category E) are infected and or have carriers within those flocks. Many carrier birds will never show a sign or symptom and your flock may never have an outbreak. Generally there is a "trigger" for a bird with MG. Weather, with extreme conditions can be a trigger as well as high stress conditions, such as poultry shows and swaps, change of environment, and adding new birds into an existing flock.

Candid Conversation about CRD/MG ...

Now that you have an understanding of what CRD/MG is, and how scary it all sounds, we can "talk". First, we are not veterinarians and the statements we make are solely our opinions on the subject. Our opinions are based on the research we have done and our personal experiences with Mycoplasma gallisepticum.

Many years ago we contracted MG in our original starter flock. Thankfully we had not started breeding or hatching. We chose to have our birds tested to confirm our suspicions, knowing MG was reportable. We destroyed 200 birds. We were able to maintain a separate building that repeatedly tested negative. It was a very stressful time for us, but through our experience we feel we gained a great deal of knowledge and understanding. 

We chose to destroy our birds, we felt as responsible breeders it was our only option. The reality is MG is WORLDWIDE!  The work in producing MG free commercial stock is very important as we need the commercial poultry industry to feed the masses. However, if the same requirements were made for the small exhibitors flock it is reasonable to suggest that almost all non- commercial poultry would be lost. Most of us do not want to just have Leghorns and Cornish crosses in our backyards. MG is out there, that is a simple fact. Starting our breeding flocks over we had to do the same process the commercial industry started out with. We treated all hatching eggs with a Tylan shock dip to erradicate the MG bacteria from our future breeding stock.

 The truth is, this bacteria can be tracked in through vehicle tires, wild birds and many other ways. Good bio-security, having separate buildings for chicks and using proper integration methods can keep your flock healthy. For the small backyard poultry owner that has an outbreak it is easily remedied by treatment of symptoms and you can still enjoy your birds. For the larger poultry farm and one that breeds and sells to the public it is best to cull birds that are suspect. Avoiding shows, swaps, and other peoples poultry yards will help in the prevention of MG into your flock. Most poultry owners have MG in their flocks and do not know it. Many birds may live their life without ever showing a symptom. Those that show will often put their birds on an anti-biotic prior to a show and then again for 10-14 days after a show. 

Many poultry breeders and enthusiasts have never heard of MG. Many have heard the term "chicken cold" and have experienced a "cold" in their flock. The chicken cold is more than likely MG. Be aware that there are many breeders who DO know they have MG in their flocks, continue to breed and do not attempt to "clean-up" their flocks. Destroying a flock and starting over is an expensive proposition and can take considerable time. No breeder can afford to have to continually start over again and again. One rather well known show breeder we talked to was disgusted that we would destroy our flock. This breeder simply found it acceptable to continually use anti-biotics on her birds and sell birds and hatching eggs with no thought as to the those purchasing her birds/eggs. It is our opinion, that although it is unrealistic for a breeder to continuosly "start over", all known birds and birds that have continuous outbreaks should be culled. 

As a producing flock we take great care and have a strict protocol for rearing our birds. We strive for healthy, long lived, disease free birds. The very nature of the bacterium means that we cannot guarantee MG free birds. ONLY flocks CERTIFIED MG CLEAN by NPIP can be considered "clean". We can say, we monitor our flocks health continuously and our birds are in excellent health exhibiting no CRD effects. We have excellent hatch rates, well shaped eggs, healthy growth of chicks and maturing birds, and our birds are anti-biotic free. We have never regretted starting over and learning about MG, and the experience has allowed us to be better breeders of these amazing creatures.

If you suspect you have MG in your flock

 and would like support or would like to know more about prevention, contact us .