Fatty liver hemorrhagic syndrome (FLHS) is one of the leading causes of mortality for laying hens, mainly those housed in cages. This disease is observed mainly in hens in the middle and late stages of egg production.
During a post-mortem examination, severe fat buildup is noticed in the abdominal cavity and the visceral areas.
The liver is swollen, spherical, and extremely delicate or fragile.
Due to fat accumulation, its color changes from pale brown to yellow.
This condition commonly results in liver rupture, hemorrhages, and unexpected mortality due to internal hemorrhages.
It is relevant to remember that death from FLHS occurs only in extreme cases following massive liver hemorrhage, suggesting that a significant number of hens within a flock might suffer from “sub-acute and chronic FLHS”. The chronic form of FLHS may cause a drop in egg production but little or no change in mortality. These hens may show reproductive dysfunction.
In 2021, researchers from Hebei Agricultural University in China concluded that liver metabolites and arachidonic acid metabolism were linked to the pathophysiology of FLHS. Hens with FLSH have significantly higher levels of metabolites like alanine aminotransferase, aspartate aminotransferase, low-density lipoprotein, total cholesterol, and triglycerides, decreased high-density lipoprotein, and hepatic steatosis.
The FLHS causes profound changes in liver function that can be detected by blood tests (Table 1).
In the layers with FLHS, liver carnitine and stearoyl carnitine are reduced.
As an essential factor in fatty acid metabolism, carnitine plays a key role in fatty acid transportation into mitochondria for oxidation.
The conditions of fatty liver disease promoted fatty acid oxidation to provide energy, accompanied by carnitine consumption.
Table 1. Blood metrics of hens depend on the incidence of FLHS
Environmental factors that increase incidence
Data from diverse surveys and controlled studies worldwide have revealed that housing systems do not affect mortality rates or that mortality rates are lower in conventional cage systems than in free-range or organic systems. However, the cause of death is well related to the cage system. The most common cause of death in conventional cages is FLHS, with 58 to 74% of necropsied hens dying from this condition.
Conventional cage systems have decreased worldwide due to welfare concerns and governmental regulations, but they are still the predominant housing system wor...
