Very high energy levels in layer diets over a prolonged time. Excess energy is stored as fat in the liver. Layer diets and intake of birds need to be monitored closely during the laying period. Usually a reduction in energy level of the diet, allowing birds to use some of the energy stored in the liver, reduces the condition.

FLS is in the most cases a physiologically problem. A very good treatment you can make with Carnitine.

The fatty liver haemorrhagic syndrome (FLHS) is a widely prevalent sporadic disease mainly among commercial layers. 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.

please fine the attached link

http://www.thepoultrysite.com/publications/6/diseases-of-poultry/219/fatty-liver-haemorrhagic-syndrome

It is mainly due to high energy level, nutrient deficiency (biotin, choline etc), toxins in feed etc

Supplement Nutrients (Choline, Vitamin E, B12 and Inositol) 

dilute the feed

Use Liver tonics containing betaine

excessive feeding with lack of proper exercise (esp caged hens) is one of the main predisposing factor of FLHS. It is also associated with environmental stress and hormonal imbalance that mostly happens in high producing birds. Low protein diet, toxin in feed may also be important in making birds susceptible to FLHS. It can be best managed by proper monitoring of feed intake, production and allowing birds to do excercise and including Vit E, Se. Livertonic may also be of help.

If protein to energy ratio is maintained and diets balanced with dAAs, low protein diet is not a predisposing cause of FLHS.

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.