Multicausal Respiratory Disease Com ...

Multicausal Respiratory Disease Complex in Laying Hens

Respiratory Disease Complex or Multicausal in Laying Hens

Happenings / Clinical Signs

Although much is known about the individual agents responsible for respiratory diseases in poultry, uncomplicated infections with single agents are the exception. Under commercial conditions, complicated infections involving multiples aetiologies with viruses, mycoplasmas and other bacteria, immunosuppressive agents, and unfavourable environmental conditions are more commonly observed than simple infections. In addition, respiratory reactions induced by routine vaccination programs may themselves play a major role in the development of respiratory disease.


  • Low mortality or increases gradually
  • Poor body fleshing condition if  birds survive the initial infection
  • Most mortality occurs after the respiratory infection

Visibly sick birds

  • Few visibly sick birds
  • Birds with persistent anorexia become emaciated and die


  • Respiratory signs spread slow
  • Respiratory signs are usually mild
  • Respiratory signs usually occurs five days after administration of a live vaccine (IBV) or (NDV)


  • Dirty vents may be present


  • Dirty or Pasty vents or feathers with droppings around the vent may be present
Causing Agents
Multifactorial. Cold environment. Respiratory viruses. Secondary bacterial infection. Live respiratory virus vaccines. Immunosuppression. Dust, ammonia. Stress factors
Affected Systems/Organs
Respiratory and Reproductive System
Transmission via aerosols, dust, water.
Mainly Affects
Egg Production and Liveability
Good management. Control factors
Suggested Actions
  • Technical assistance recommended
  • Can be managed with feed additives, off-the-shelf medications
  • Diagnosis should be confirmed with rapid assays and/or a certified laboratory
  • Veterinary intervention is recommended
  • Can be managed with vaccination programs.

Impact on Egg quality


Impact on Liveability


Impact on Production


Overall Economic Impact


Y.M. Saif.2008.Disease of Poultry. 12th Edition. page 707

David E. Swayne. 2013.  Diseases of Poultry 13th Edition. page 775

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