Fatty Liver Hemorrhagic has a bunch of potentially contributing causes, though based on the studies I've read, in a typical chicken diet, one is more likely to hit the high fat (or the high fat + high carb) levels associated with increased incidence of the sndrome before one hits the high...
Shrimp shells work well as treats - but BE MINDFUL of the salt content. I don't boil mine in salted water (or old bay - which is mostly various salts), so the shells are fine from "peel and eat" night.
"Fatty Liver Hemorrhagic Syndrome'
Also
Here
and here
and easily several dozen other reasonably reliable sources I could quickly link. The important thing to remember is that we (and bears, seals, and whales, and other cold adapted mammals tend to put on layers of fat subcutaneously...