Fatty liver syndrome (FLS), also known as hepatic lipidosis, is seen commonly in overweight hens on a poor diet. FLS is very similar to nonalcoholic fatty liver disease (NAFLD) in humans, and have been used in research studies as an animal model for the disease. The liver is a vital organ, and is responsible for multiple metabolic roles. When a chicken develops FLS, it means that their normal liver cells are gradually accumulating fat which causes them to no longer work efficiently and 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 onset of clinical signs.
Influencing factors that cause increased risk for chickens to develop FLS include:
- Low-protein high-fat (LPHF) diet: Chickens on a low-protein (less than 17.5% Crude Protein) diet. Risk is further increased if the diet is also high in fat (greater than 3.5% Fat). This is related to the fact that birds have a unique method of removing lipids from the liver. Thus, when birds have a protein deficiency, usually related to inadequate amino acids, it results in the buildup of lipids and the formation of fatty liver.
- High-energy diet: Chickens on a high-energy feed with corn (maize) as the predominate ingredient. Incidences of FLS were reduced in laying hens that were fed a low-energy barley diet, especially during the summer months.
- Increased age: Older hens are more likely to develop FLS than young hens, regardless of their diet. In addition, older hens tend to have more severe accumulations of liver fat content.
- Hormone imbalance: Increased estrogen levels are an important factor in the accumulation of fat in the liver. Laying hens are predisposed to hormonal imbalances involving estrogen levels, due to fluctuations involved in the egg laying process.
- Heat stress: Exposure to excessive hot weather conditions.
Clinical signs include both nonspecific and liver disease associated. Nonspecific signs include lethargy, weight loss, reduced appetite, increased water consumption, poor feather condition, and dyspnea. Liver disease associated signs include abdominal swelling due to hepatomegaly or ascites secondary to hypoalbuminemia, coagulopathies, melena, abdominal beak and nails, abnormal color in the feathers caused by lack of pigment synthesis, and green or yellow feces caused by excessive biliverdin or bilirubin.