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 an abdominal enlargement. The combs may be pale, shriveled, or occasionally cyanotic. (1, 2, 3)

Mortality tends to be chronically higher than normal for a prolonged period. Morbidity (percentage of sick birds) is low. (1, 2, 3)

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

Dead birds

  • Poor bodily  condition
  • After clinical signs develop, the course of the disease is usually rapid, and birds die within a few weeks. Other affected  birds may die without showing obvious signs


  • Diarrhea
  • In some instances or sometimes it is difficult to observe diarrhea in live birds but generally, the dead birds may show diarrhea signs

Head Comb Wattles Face Nostrils Sinuses Mount Beak Earlobes

  • The comb may be pale
  • Comb shriveled
  • Comb occasionally 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
  • Dehydration

Feather Abnormalities

  • In erythroblastosis and myeloblastosis, haemorrhage from feather follicles also may occur

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

  1. Egg drop
  2. High mortality or increases rapidly
  3. Dead birds in good bodily or fleshing condition
  4. Many visibly sick birds
  5. Flock behavior activity change
  6. Respiratory abnormalities
  7. Neurological Nervous
  8. Lameness or unusual movements, incoordination, ataxia
  9. Eyes 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


  1. Y.M. Saif.2008.Disease of Poultry. 12th Edition.page 531
  2. David E. Swayne. 2013.  Diseases of Poultry 13th Edition. page 570
  3. Mark Pattison, Paul F. McMullin, Janet M. Bradbury. Dennis J. Alexander. 2008. Poultry Diseases. 6th Edition. 284
  4. Paul McMullin. 2004. A Pocket Guide to Poultry Health and Disease. First Edition.
  5. Steven Leeson, John D. Summers. 2008. Commercial Poultry Nutrition. Third Edition.
  6. Donald D. Bell, Williams D. Weaver. 2009.  Commercial Chicken Meat and Egg Production. Fifth Edition.
  7. Gail Damerow 1994. The Chicken Health Handbook.

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