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Fatty liver disease

Fatty liver disease

Fatty liver disease: Fatty liver haemorrhagic syndrome (FLHS) is a metabolic condition that occurs in commercial layers and is frequently the major cause of death in high producing laying flocks. 
FLHS is characterised by excessive fat in the abdomen and liver, and haemorrhage from a ruptured liver. The syndrome occurs in caged laying hens, primarily in birds that are in positive energy balance. Outbreaks occur sporadically in commercial flocks, and 3 - 5 % of the affected flocks die from the condition. 

The decrease in egg production and increase in mortality associated with FLHS have implications for the welfare of hens and cause considerable economic losses to egg producers. 

Example: a farmer has 2,000 chickens and he gets an outbreak of FLHS, how much does it cost him? (click on the table to enlarge)

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Symptoms

The liver is a vital organ, and is responsible for multiple metabolic roles. When a chicken develops FLHS, it means that their normal liver cells are gradually accumulating fat which causes them to no longer work efficiently. Over time these liver cells may be destroyed. As the cells die, they are replaced with scar tissue or fibrous connective tissue. 

Affected birds may appear as if they suddenly became ill. However in reality, the condition has most likely been building up until the bird's liver and other organs can no longer compensate, resulting in the clinical signs. The onset of FLHS in chickens is influenced by several nutritional, metabolic, environmental, genetic, and hormonal factors.

The FLHS outbreaks are often associated with hot weather and a period of extensive egg-laying. The hens in the flock are overweight (on the average by 20 % or more) and a sudden drop in egg production is observed. The birds are discovered suddenly dead, with pale head skin. In the abdomen, large blood clots are detected. 

It is difficult to see if a hen has FLHS when the hen is alive. Signs which indicate that chickens are suffering from FLHS include:

  • Obesity
  • Difficulty breathing
  • Distended, enlarged abdomen
  • Decreased egg production 
  • Paleness 
  • Dandruff on combs 
  • Greenish diarrhea 
  • Lethargic 
  • Sudden death

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Predisposing factors

FLHS is a so called multi-factorial disease, this means that it is caused by numerous factors related to nutrition, hormonal factors, housing conditions and genetics. 
The fat content of the liver of laying hens increases under normal metabolic conditions of egg laying. The additional effects of environmental factors - including excess energy intake and confinement - appear to alter liver function and utilisation of fat and therefore induce FLHS. 

Feed
FLHS is highly influenced by the feed. Factors that puts chickens more at risk to develop FLHS are:

  • Chickens on a low-protein (less than 17.5 % Crude Protein) diet are more at risk of developing FLHS. When birds have a protein deficiency, usually related to inadequate amino acids, it results in the buildup of fat and the formation of fatty liver.
  • Risk is further increased if the diet is also high in fat (more than 3.5 % Fat). 
  • High-energy diet: Chickens on a high-energy feed with corn (maize) as the predominate ingredient are more at risk of developing FLHS. 
  • Older hens are more likely to develop FLHS than young hens, regardless of their diet. 
  • (Heat) stress: Exposure to excessive hot weather conditions or other sources of stress increases the risk of sudden death in hens with FLHS. 
  • The exposure to mycotoxins in the feed increases the risk of FLHS.

Diagnosis

Signs that a hen has FLHS are very difficult to identify while the bird is alive. However, it is usually easy to see during necropsy. FLHS-affected chickens develop gross lesions of the liver that are characterized by enlarged, friable, soft, and varying in color from tan to yellow to orange. Haemorrhaging is usually present in varying amounts. Sometimes blood clots are observed in the abdominal cavity, originating from the liver. The liver color and amount of haemorrhaging present usually is in direct correlation with the amount of fat accumulation in the liver. To diagnose FLHS, the major laboratory in The Netherlands, GD animal health, has developed a “Fatty liver combination test”. With this test, it is possible to differentiate whether the chickens have FLHS and if it is necessary to start treatment. This test is now available at Kepro.
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To do the test, you need to select some chickens which are suspected to have FLHS. On these chickens you need to do a post-mortem examination, and use the color combination chart to check the color of the liver. Possible outcomes can be “no treatment required”, “testing required” or “treatment required”. If the test indicates “no treatment required”, it is necessary to...

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