Fatty liver hemorrhagic syndrome (also referred to as fatty liver syndrome or FLHS), a disease in chickens and other birds. Birds with this disease have large amounts of fat deposited in their liver and abdomen. [1] This often results in an enlarged liver that is easily damaged and prone to bleeding. [2] In some cases the disease is fatal, usually as a result of blood loss from an internal hemorrhage in the liver. [3] The hemorrhage often occurs when a hen is straining to lay her egg. [2] Fatty liver hemorrhagic syndrome is "the major cause of mortality in laying hens." [4]
Excessive dietary energy intake is believed to be the cause of fatty liver hemorrhagic syndrome. [2] Heredity may also play a role, but it is not the entire cause for the disease. [3] Birds housed in cages will more likely be affected because they are unable to exercise to burn off the extra dietary energy. [2] A 2019 study showed 74% of caged hens died from FLHS whereas only 0–5% of mortalities in hens from cage-free barn or free-range systems were attributed to this condition. [5] Walking hens are less likely to develop this problem. The disease is observed most often in birds that appear to be healthy and in a state of high egg production. [2] As a result, death can occur quite unexpectedly.
Affected birds are usually overweight and may also have pale combs. [1] Generally, however, the disease has few or no symptoms prior to the bird's death. [6]
Additional information needed The use of L-Tryptophan in the diet can decrease the syndrome. [7]