Fatty Liver Syndrome – could this “silent killer” be affecting your egg production?

11 January 2021

Fatty Liver Syndrome (FLS) is an underdiagnosed disease that occurs when there is a mismatch between energy intake and energy requirements. FLS can result in a drop in egg production/egg mass and an increase in mortality.

When and why does Fatty Liver Syndrome occur?

FLS typically occurs at two key economical moments during the laying cycle: immediately before or at peak production and/or at the end of the laying cycle. During peak production, young hens are not always able to increase their feed intake to a level that meets the energy requirements for egg production. They have high levels of oestrogen, and are in a negative energy balance. As a result, they will start to convert carbohydrates to fatty acids - a process which takes place in the liver. If transport of fatty acids out of the liver cannot match production, fat starts to accumulate in the liver, resulting in FLS. At the end of the laying cycle, lower egg production results in lower energy requirement of the birds. If feed intake is not reduced, excess carbohydrate is metabolised into fatty acids in the liver, resulting in an increase in fat deposition in the liver, and in FLS.

Indicators of Fatty Liver Syndrome

FLS can present itself in different ways. In some farms, FLS results in a drop in egg production of 25-30% with almost no mortality.  In other farms FLS may result in mortality as high as 5%, with a drop in egg production of the surviving birds of only 5-10%. Next to the drop in egg production and the increase in mortality, flocks suffering from FLS can have birds with sunken eyes and pale to yellow combs. These are all very common symptoms, and if FLS is suspected, a diagnosis can be made by necropsy with help from your vet. Enlarged, pale and friable livers with abnormal amounts of fat in the abdominal cavity will be found. Liver fat percentage in birds suffering from FLS can be as high as 70%. Livers of affected birds become very fragile and liver damage, particularly bleeding, is common.

Factors increasing the risk of Fatty Liver Syndrome and how to avoid it

It is not fully understood why FLS occurs in some flocks and not in others. There are, however, a number of risk factors associated with the problem. 

Activity level - If birds are active, the energy requirements for maintenance are higher, so they use their fat reserves to produce energy, which reduces the risk of accumulation of fat in the liver. FLS therefore occurs more often in caged birds compared to free range animals and during periods of high temperature as this reduces activity levels of birds. Countries/seasons with shorter periods of daylight, as birds are less active when it is dark, also increase risk.

Diet - Several factors associated with diet can increase the risk of developing FLS. Overfeeding (feed intake should be aligned with the energy content of the feed, avoiding an excess energy intake), an incorrect balance between protein and energy, high levels of carbohydrates (i.e. starch) and insufficient levels of unsaturated fatty acids (i.e. linoleic or arachidonic acid) should be avoided, amino acid composition of the diet should be correct, and diets should contain enough choline, methionine and vitamin B12 as these are vitamins that stimulate fatty acid transport from the liver.

Exposure to harmful substances - There are a number of substances that can have a negative impact on liver function and on fat metabolism, resulting in FLS. Examples are moulds, mycotoxins, bacterial toxins and certain pesticides.

Stress - Stress reduces liver function, which may result in accumulation of fat in the liver.

Farm-O-San FLS can help prevent and improve symptoms of fatty liver syndrome in laying hens. It contains a number of ingredients with proven benefits for layers and breeders at risk of developing FLS. Poly Unsaturated Fatty Acids (PUFA’s) are an alternative source of energy for the hens, which reduce the conversion of carbohydrates to fatty acids in the liver. A number of vitamins, such as choline and vitamin B12, maintain proper fat transport out of the liver as lipoproteins. Biotin and vitamin B1 improve carbohydrate and glucose utilisation and stimulate carbohydrate and energy metabolism. Lastly, FLS contains vitamin E, selenium and AO Mix, which have antioxidant activity that birds with FLS benefit from by maintaining a correct free radical balance.

Dr. Sophie Prentice                                                                                                          Monogastric Feed Additive Product Manager