Whats wrong with suet cakes?

[2DogsFarm]

I put a suet cake out for my girls about a month ago and they LOFFED it!

Yesterday I picked up another one - figuring they could use the extra calories in the colder weather - and after I put it down for them I read the wrapper that stated:
"do not feed to domesticated birds"
Huh?

What could be in a suet cake (with fruit & nuts) that could harm a chicken?

 

[canada-goose]

I'm sure the occasional junk food treat won't hurt them. Just don't give them suet cakes every day and you should be fine.

 

[deerman]

My guess, they put something in them. That you would not want to eat the bird or the eggs. Way to protect themself from a law suit.