Avian Lymphoid Leukosis (LL) in Lay ...

Avian Lymphoid Leukosis (LL) in Laying Hens

Avian Lymphoid Leukosis (LL) in Laying Hens

Outward signs of the leukotic diseases are mostly non-specific. They include inappetence, weakness, diarrhea, dehydration and emaciation. In Lymphoid Leukosis, especially, there may be abdominal enlargement. The combs may be pale, shrivelled, or occasionally cyanotic.

Mortality tends to be chronically higher than normal for a prolonged period. Morbidity (percentage of sick birds) is low.

Observed Clinical Signs Happenings

Visibly sick birds

  • Few visibly sick birds
  • Weakness
  • Inappetance
  • Dehydration


  • Low mortality or increases gradually
  • Birds die within a few weeks
  • Other affected birds may die without showing obvious signs

Head Comb Wattles Face Nostrils Sinuses Mount Beak Ear lobes

  • Comb may be pale
  • Comb shriveled
  • Comb occasional cyanotic

Body Parts (Neck, wings, breast, abdomen, shanks, legs, hocks, feet, joints, vent, and skin, abnormalities), skinny body, retarded growth, weight depression

  • Abdominal enlargement
  • Emaciation
  • skinny body


  • Diarrhea

Avian Lymphoid Leukosis (LL) in Laying Hens DOES NOT exhibit or manifest any of the following clinical signs happenings:

  1. High mortality or increases rapidly
  2. Dead birds in Good body fleshing condition
  3. Many visibly sick birds
  4. Flock behaviour activity change
  5. Respiratory abnormalities
  6. Neurological Nervous
  7. Lameness or unusual movements, incoordination, ataxia
  8. Eyes abnormalities
  9. Feathers abnormalities
  10. Feed Consumption Changes
  11. Diet or Feed Changes (Recent Feed delivery, Recent formulation /diet, Other silo or improper storage, Another feed brand)
  12. Shell quality defects
  13. Internal Egg defects


Causing Agents
Viral disease. Virus (Retroviridae family), Neoplastic Disease. Lymphoid Leukosis. These are the oncogenic virus (otherwise known as oncoviruses or tumor viruses).
Affected Systems/Organs
Tumors invariably involved: Bursa. Liver. Spleen, Kidney and others visceral organs.
Congenital (from parents) transmission is most important. Bird to bird transmission is poor but infection may occur through the feacal oral route.
Mainly Affects
Biosecurity, all-in/all-out production system. Control arthropods. Hygiene.
Suggested Actions
  • Can be confirmed with clinical signs and gross lesions
  • Diagnosis should be confirmed with rapid assays and/or a certified laboratory
  • Veterinary intervention is recommended

Impact on Egg quality


Impact on Liveability


Impact on Production


Overall Economic Impact


Y.M. Saif.2008.Disease of Poultry. 12th Edition.page 531

David E. Swayne. 2013.  Diseases of Poultry 13th Edition. page 570

Mark Pattison, Paul F. McMullin, Janet M. Bradbury. Dennis J. Alexander. 2008. Poultry Diseases. 6th Edition. 284

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