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Chronic respiratory disease (CRD) is one of the most common respiratory diseases of poultry. The disease occurs when birds infected with Mycoplasma gallisepticum are stressed. The subsequent invasion by secondary bacteria causes the major damage to the bird.
Scientific name
Mycoplasma gallisepticum plus other organisms
Cause
- Mycoplasma gallisepticum
- + Chronic stress factor
- + Secondary coliform organisms
Species susceptible
- Chickens
- Turkeys
Incidence
Very widespread and present in most commercial flocks
Transmission
CRD is the most prevalent of the so called 'stress diseases' and outbreaks occur most frequently at times of stress:
- Moving
- Chilling
- Vaccinating
- Beak trimming
- Worming
- Poor ventilation
- Damp litter
- Ammonia build-up
- Other diseases
However, transmission may occur in flocks that appear to be perfectly healthy.
1. Egg Transmission2. Airborne (aerosol)Major importance as the means by which the disease perpetuates itself
3. Indirect or mechanicalGenerally rapid, but does not travel long distances
- Infected Carrier birds
- Persons such as service personnel
- Vaccinators and blood testers
- Equipment (crates, vehicles, and vaccinating equipment)
Incubation period
Incubation is 5 to l0 days.
Symptoms
- Sniffing
- Rattling
- Sneezing
- Coughing
- Wet noses
- Retarded growth in growing birds
- Production loss (20 to 30%) in hens
- Deaths are few in uncomplicated cases
The disease spreads slowly through the flock and there is a continual cycle of re-infection so that the disease never disappears by itself.
Financial losses are due to:
- Poor feed conversion
- Retarded growth
- Drug costs
- Mortality
- Increased culling
- Poor production
Diagnosis may prove tricky
- Isolation of mycoplasma is difficult
- Must be confirmed to be Mycoplasma gallisepticum (other types of Mycoplasma exist)
- Blood tests vary in reliability
Post mortem
- Mucus in the trachea, sinuses and bronchi
- Cloudy, thickened air sacs
- Perihepatitis
- Pericarditis
Similar diseases
- Coryza
- Infectious bronchitis
- Infectious laryngotracheitis
- Fowl cholera
Treatment
1. Antibiotics:
- Help control the disease
- Minimise secondary bacterial complications
- Do not control the disease completely
2. Flock management:
- Control stress factor
- Hygiene
- Isolate young birds from older birds
- Isolate affected groups (50 to 100m apart)
- Buy vaccinated pullets
- All-in, all-out management
Prevention
1. Antibiotics:The organism may be present in a flock without producing any signs of disease. It will spread slowly to other birds until the birds are 'stressed' when it will spread more rapidly.
=> Where CRD is a problem: Treat the flock before the birds are stressed
- In the first 3 days of life
- At four weeks of age
- At maturity
These measures may not prevent the disease but will lessen the likelihood of an outbreak.
2. Vaccination:Pullets reared in isolation can be vaccinated to prevent infection with Mycoplasma gallisepticum.
TAG : Poultry, Chicken, Turkey, Mycoplasma, Bird
When you say that transmission is often via eggs, does this mean that infected birds will lay infected eggs, which will hatch into chicks that are carrying the disease? I began with poultry in May, hatching all my own eggs, and ended up with a very large percentage of the flock suffering. However, we did notice that some clutches suffered more, or faster than others. I imagined that they were more susceptable, but now wonder if the eggs were infected?
One of the most visible symptoms of CRD that I noticed in the broilers that I am raising was they had their mouths open at least 3 to 5 days before the disease started causing heavy casualties. I thought that they were feeling too hot or something when in fact they were sick and we were late in giving them medication on time.