Chronic Respiratory Disease (CRD)

​​​​CRD is one of the most common causes of disease in backyard fowls, occuring when chickens and turkeys that are infected with Mycoplasma gallisepticum are stressed. The bacteria then causes major damage to the bird's respiratory system.​

M.​ gallisepticum spreads via eggs, airborne transmission and indirect or mechanical routes such as introducing infected birds to an existing flock, or via bird transport containers. M. gallisepticum can reside in a flock with few indications of its presence until the flock or individuals in it are stressed sufficiently to show signs of respiratory disease.

Signs of CRD

The signs of CRD are sniffling, sneezing, coughing and other signs of respiratory distress. When suspected, observe the birds from a distance to get a good idea of the symptoms as birds often do not display signs of disease once caught.

Sometimes CRD slowly spreads through the flock causing poor production, retarded growth and wet noses. In these cases there are usually few mortalities unless the underlying stressors increase.

Similar Diseases

Other diseases that have similar clinical signs are Coryza, Infectious bronchitis, Infectious laryngotracheitis and Fowl cholera.


There are antibiotics that can help to control the disease but reducing stress is an essential component to managing the disease once it is in the flock. Ask your veterinarian about appropriate treatments.


Point-of-lay pullets that are vaccinated against CRD are available from suppliers - make sure you ask about the vaccination status of the birds you are acquiring.

Management issues must be addressed before the birds arrive. Ensure birds are free of M. gallisepticum on introduction. An all-in, all-out system with thorough cleaning down between batches and acquiring vaccinated birds helps. Ensure the nutrition and flock dynamics (size, age distribution, presence of roosters etc) are also optimal. Housing that is difficult to clean and thus accumulates manure, dust and vermin leads to many common ailments in poultry.

For further information:


Animal Disease Enquiries

13 St Johns Avenue,
New Town, TAS, 7008.