Avian Lymphoid Leukosis (LL) in Lay ...

Avian Lymphoid Leukosis (LL) in Laying Hens

Avian Lymphoid Leukosis (LL)  in Laying Hens

Happenings / Clinical Signs

Outward signs of the leukotic disease are mostly nonspecific

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

Neck wings breast abdomen shanks legs hocks feet joints vent skin

  • Abdominal enlargement


  • Diarrhea

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, shriveled, or occasionally cyanotic.

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

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.

Paul McMullin. 2004. A pocket Guide to Poultry Health and Disease. First Edition.

Steven Leeson, John D. Summers. 2008. Commercial Poultry Nutrition. Third Edition.

Donald D. Bell, Williams D. Weaver. 2009.  Commercial Chicken Meat and Egg Production. Fifth Edition.

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