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Fatty Liver (Photo: BIOMIN / Filipe Ribeiro)

Fatty liver

Birds afflicted with fatty liver syndrome present general obesity (on the average 20% overweight) with enlarged, fat-infiltrated livers, which are soft and easily damaged. Variable low mortality (2-5%) may be observed, caused by internal liver hemorrhage. In that case, birds will be found suddenly dead with pale head skin.

Liver function in poultry

The liver has various functions in digestion, metabolism and absorption, for example, metabolism of chemicals, absorption of protein, digestion of fat, metabolism of carbohydrate and absorption of vitamins. Almost all chemicals, including toxin components in the feed and chemical compounds in medicine are also metabolized and detoxified by the liver. All amino acids that are absorbed by the intestinal tract move to other organs through the portal vein in the liver, and catabolism of excess amino acids, uric acid formation from ammonia and albumin formation are also a major event occurring in the liver.

As glycogen, an intermediate metabolite of carbohydrate, is synthesized and stored in the liver, it plays a major role in glycogenesis together with the pancreas.  Fat soluble vitamins are also absorbed and stored in the liver. Erythropoiesis, the production of red blood cells, is also an important function of the liver. The liver thus performs numerous functions to maintain a proper body system, but poultry in modern production systems are facing a lot of challenges that threaten liver health.


Evaluating liver health

Although the liver has so many essential functions for bird health,  'physiologically normal' livers are rarely seen in field conditions because of frequent medication and exposure to toxic materials from the feed and the environment. Observation of liver color is the easiest and most reliable way to evaluate liver health. The liver could show various colors according to age, fat deposition, necrosis caused by viral infection, yolk absorption at an early stage and various other factors.

Liver color observation should be done with a fresh sample within 30 minutes post mortem. Color changes in the liver could occur post mortem due to movement of red blood cell by force of gravity.

A healthy liver shows a yellow color until 8 to 10 days of age because of yolk content absorption, but gradually changes to a brown color with age. Here then, a yellowish brown color would be regarded as an abnormal color of the liver, but it does not always signal pathological conditions that require treatment.

Yellowish colored liver of 4 day-old chick
Yellowish colored liver of 4 day-old chic

Fatty liver syndrome

Fatty liver syndrome is a non-infectious condition that affects laying or breeding hens, especially caged animals. Some strains appear to be more susceptible than others, higher producing hens are the most susceptible within a flock and outbreaks of the problem are often associated with hot weather and a period of extensive egg laying.

Usually, the cause is related with high calorie intake (high energy diets or incorrect energy: protein ratios) but other factors, such as intake of the hepatotoxic aflatoxin or mismanagement of layer birds must not be disregarded.

In case exposure to is to blame, commonly known as lean bird fatty liver, livers are yellowish with petechial hemorrhages but not swollen; microscopic lesions of centrilobular necrosis and bile duct hyperplasia are present, but no excessive abdominal fat is found.

Several similar conditions can be related to fatty liver in poultry, namely: 

  1. Fatty Liver Hemorrhagic Syndrome (FLHS) 
  2. Fatty Liver and Kidney Syndrome (FLKS)

Fatty Liver Hemorrhagic Syndrome

Fatty Liver Hemorrhagic Syndrome (FLHS) is a metabolic disease commonly occurred in long-lived birds including breeders and layers. Lipogenesis and secretion of lipoproteins are natural metabolic functions of the liver for accumulation of energy, and these are controlled by estrogen. FLHS occurs when the accumulation of fat in the liver is increased beyond its storing capacity, and it sometimes causes hepatic rupture and bleeding.

Fatty Liver Hemorrhagic Syndrome is commonly seen in overweight birds during the laying cycle, and causes egg production drops with low mortality. High energy diets with high calorie/protein ratio, low calcium consumption, stress and mycotoxins are common predisposing factors that can facilitate the occurrence of FLHS. As a color change to yellow is an early sign of FLHS, regular monitoring during necropsy is recommended to detect the early phase of fatty liver.

Common gross lesions observed in birds with Fatty Liver Hemorrhagic Syndrome
Common gross lesions observed in birds with Fatty Liver Hemorrhagic Syndrome | Source: BIOMIN
Fatty and necrotic changes in the liver of a 40 week-old broiler breeder
Fatty and necrotic changes in the liver of a 40 week-old broiler breeder | Source: BIOMIN

Fatty Liver and Kidney Syndrome

Fatty Liver and Kidney Syndrome (FLKS) is caused by biotin deficiency at an early age, of younger than 2 weeks. Biotin, also known as Vitamin H or B7, is an essential vitamin that is important for skin formation and maintenance. Biotin deficiency in young birds causes low mortality (<2%) with skin disorders and hepatic lesions. Biotin supplementation is a treatment option that shows good prognosis.

Picture of hepatic lesions in a 4 day-old chicken with Fatty Liver and Kidney Syndrome
Hepatic lesions in a 4 day-old bird with Fatty Liver and Kidney Syndrome | Source: BIOMIN

Depending on the potential cause for fatty liver, different corrective actions are proposed (see tables below).


Potential causeChecklistCorrective action
Aflatoxin B1
  • Young animals: Fibrosis of liver leads to hardening of the organ.
  • Older animals: Hepatic lipidosis, with softening of the organ.
  • Pale friable livers seen at slaughter.
  • Histopathology of the liver
  • Origin of raw materials from supplier/region with history of Afla contamination.
  • Check average contamination levels.
  • Positive for Afla in raw materials (ELISA) or feed (HPLC).
  • Prevent mold growth, purchase clean raw materials.
  • Avoid contamination of feed bins or feed/water lines by stale, wet or moldy feed.
  • Add an effective mycotoxin deactivator in the feed.


Potential causeChecklistCorrective action
Energy: protein balance

Excessive energy in diets can cause lipidosis and fatty liver problems.

  • Carbohydrate level in diet.
  • Energy-protein ratio in diet.
  • Avoid high carbohydrate diets, especially in summer.
  • Adopt proper energy-protein ratio.
Poor quality fat in the diet

Peroxides can impair the liver activity, creating fatty liver.

Quality of fats in term of peroxide value, rancidity and free fatty acids.
  • Avoid low quality fats.
  • Use low quality fats in the grower/finisher phases.
  • Replace animal fats with vegetable fats.
Choline / biotin deficiency

Pale friable livers seen at slaughter.

AA scale at feed mill.Increase level of synthetic amino acids in the diet.


Potential causeChecklistCorrective action
Viral hepatitis
(IBH – Viral inclusion body hepatitis)

Adenovirus causes yellow/hemorrhagic liver and focal necrosis. Symptoms include immunosuppression, diarrhea, anorexia, depression, ruffled feathers, especially in the region of head and neck.

  • Necropsy: Macroscopic lesion in the enlarged, dystrophic liver with yellowish color and crumbly texture; enlarged kidneys.
  • Histopathology: Detection of intranuclear inclusion bodies.
  • Isolation of serotype I or II or III from the lesions by serological assays.
  • Use inactivated vaccines (exist only for group I).
  • Check the breeding stock and eliminate the affected birds.


Potential causeChecklistCorrective action
Full fed broilers at slaughter

High lipid concentrations in the blood at slaughter can lead to paler livers.

 Fast birds before slaughter.
Hormone status

An over-stimulation of egg production may lead to excessive levels of estrogen in blood that facilitate fat storage in the liver and occurrence of fatty liver, especially in layers and breeders.

Management of laying birds (excessive estrogen stimulation).
  • Improve management of laying birds.
  • Correct lighting program.

Find this handy checklist and more in our Science & Solutions special issue.



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