CRD-Chronic Respiratory Disease in Chickens-Mycoplasma gallisepticum (MG)
Mycoplasma gallisepticum (MG) is a bacteria-like organism that causes respiratory disease primarily in chickens and turkeys but it can also infect gamebirds, pigeons, ducks, geese, peafowl and wild birds. Respiratory infections and disease usually happen in the fall and during or right after extreme weather changes. MG infection in chickens is also known as Chronic Respiratory Disease (CRD, and chickens who are exposed to it will carry the disease for the rest of their lives even if (after treatment) they do not show signs of it anymore. Birds who have been exposed or recovered from MG should not be used as breeding stoc. "MG does not make people sick and eating eggs from infected birds will not hurt you. Do not use eggs from birds that have been treated with antibiotics" (1). Starting your flock with NPIP certified birds, keeping their feed,water and coop clean, sanitized, dust free and ventilated goes a long way to prevent respiratory illness in Chickens. See Symptoms and treatments below.
How to tell if your chickens have CRD
Symptoms of Chronic Respiratory Disease in Chickens are:
- Mild Lesions
- Coughing
- Sneezing
- Rales
- Difficulty breathing
- Foamy eyes
- Reduced growth rate
- Loss of egg production
Causes-How Chickens Get MG
MG cannot survive long without a host (your chicken) but can survive long enough to contaminate your entire flock. Causes for MG are:
"MG-infected birds can also spread the disease to clean flocks. People that work with other live birds can also bring back MG to their poultry operations on their person, clothing, footwear and equipment. People can harbor MG inside their noses for days" (1).
- High dust content in chicken coop or poultry houses
- Infected chickens can give the disease to their baby chicks, through eggs
- Breeding with an infected mate
- Can be spread through body secretions
- Nasal discharges
- Eye discharges
- Fecal matter (chicken poop)
- Contaminated egg flats, equipment, cages, tools which have been exposed to contaminated feces (chicken poop)
- Can be spread from respiratory secretions (snot) from infected birds in feed, water, and on surfaces
- Contaminated feed and water drinkers
"MG-infected birds can also spread the disease to clean flocks. People that work with other live birds can also bring back MG to their poultry operations on their person, clothing, footwear and equipment. People can harbor MG inside their noses for days" (1).
How to Prevent & Control MG
Ways to prevent Chronic Respiratory Disease in Chickens are:
- Start your flock with disease free birds from known MG free flocks
- Practice Biosecurity to keep MG out. (Wear shoe coverings, do not allow vehicles on your property, wear clean aprons, face masks, and gloves).
- Keep wild birds away from your chickens
- Keep rodents (mice, rats, etc.) away from your chickens
- If you visit other birds be sure to change your clothing, foot wear, and wear a mask for a few days when going back around your own birds.
- Vaccinate show birds and valuable breeder birds annually (once a year) and monthly right before scheduled shows or onset of lay.
- Minimize your contact with other flocks.
- Serious breeders use Dipping hatching eggs in an antibiotic cold-water bath subsequent MG testing, and strict culling of infected offspring to prevent exposure to MG.
Treatment for MG
"Birds that are infected with MG remain carriers of the disease throughout their lives.
Some antibiotics such as Tylosin or tetracyclines, fluoroquinolones (available by prescription through a licensed veterinarian) can reduce clinical symptoms but will not completely eliminate MG. More importantly, some antibiotics cannot be used for birds raised for meat and eggs. Even if birds have been treated with antibiotics, they can still spread MG to other birds. Harvesting (or culling??) meat birds may be better than treating them because treatment can be expensive. Weigh the costs and benefits of maintaining a flock with MG (which may require the continuous use of antibiotics) or depopulating the infected flocks followed by thoroughly cleaning and disinfecting the facilities and equipment and starting fresh with an MG-free flock. Practice strict biosecurity to keep your flock MG-free" (1).
"Snicks, sneezes and coughing will occur in affected birds. The flock will exhibit a decreased appetite and appear fluffed and lethargic. Premortem diagnosis can be achieved by serology, PCR, or culture and identification. Necropsy will reveal air saculitis and fibrinous polyserositis. A killed vaccine is available that will reduce clinical signs but will not prevent vertical and horizontal transmission. The standard course of treatment is injectable or water-based tylosin for a minimum of thirty days. Owners should be aware of the egg and meat withdrawal times after discontinuing antibiotic use. While clinical signs will improve, the organism is never completely cleared from the system" (Brendan Noonan, DVM, DABVP (Avian Practice) angell.org/avianandexotic).
Some antibiotics such as Tylosin or tetracyclines, fluoroquinolones (available by prescription through a licensed veterinarian) can reduce clinical symptoms but will not completely eliminate MG. More importantly, some antibiotics cannot be used for birds raised for meat and eggs. Even if birds have been treated with antibiotics, they can still spread MG to other birds. Harvesting (or culling??) meat birds may be better than treating them because treatment can be expensive. Weigh the costs and benefits of maintaining a flock with MG (which may require the continuous use of antibiotics) or depopulating the infected flocks followed by thoroughly cleaning and disinfecting the facilities and equipment and starting fresh with an MG-free flock. Practice strict biosecurity to keep your flock MG-free" (1).
"Snicks, sneezes and coughing will occur in affected birds. The flock will exhibit a decreased appetite and appear fluffed and lethargic. Premortem diagnosis can be achieved by serology, PCR, or culture and identification. Necropsy will reveal air saculitis and fibrinous polyserositis. A killed vaccine is available that will reduce clinical signs but will not prevent vertical and horizontal transmission. The standard course of treatment is injectable or water-based tylosin for a minimum of thirty days. Owners should be aware of the egg and meat withdrawal times after discontinuing antibiotic use. While clinical signs will improve, the organism is never completely cleared from the system" (Brendan Noonan, DVM, DABVP (Avian Practice) angell.org/avianandexotic).
Treating the Chicken Coop for MG
While your chickens are being treated for MG you should remove all chickens from the coop for one week. Clean and disinfect the chicken coop (preferably with bleach) floors, roosts, walls, ceilings, nest boxes, and any place that the chickens have contact with. Allow several days for the coop to air out before returning your non infected birds or new birds to it.
What to Do If you have High Mortality Rates
Call your local State Department of Agriculture, State Veterinarian's office or diagnostic lab if you have an unusually high level of mortality on your farm, the dead birds or live birds that show the same symptoms, may be submitted for necropsy to a regional MDA Animal Health Diagnostic Laboratory (1).
More About Respiratory Disease in Chickens |
References:
- Jonathan Moyle ([email protected]) and Nathaniel Tablante ([email protected]), University of Maryland Extension; Daniel Bautista ([email protected]), University of Delaware; F. Dustan Clark ([email protected]), University of Arkansas Extension. Recognizing and Preventing Mycoplasma gallisepticum (MG) Infection in Poultry. (June 2015). University of Maryland Extension. Solutions in your community. https://extension.umd.edu//sites/extension.umd.edu/files/_docs/programs/poultry/FS-1008%20Recognizing%20and%20Preventing%20Mycoplasma%20gallisepticum%20(MG)%20Infecti....pdf
- Brendan Noonan, DVM, DABVP (Avian Practice) angell.org/avianandexotic. Retrieved on Feb. 25, 2025 from https://www.mspca.org/angell_services/respiratory-disease-chickens/
