I did once read that, if travelling in hot countries in areas where there's a risk of food poisoning, a ripe avocado is one thing you can safely give to a baby or young child, as it's got so many beneficial elements in it. Same with bananas I suppose. But not for chickens!
Mind you, in the unlikely event of anyone actually feeding avocados to chickens, I would imagine they wouldn't be keen to eat them anyway, if harmful. All those lists of things you're not supposed to grow in your garden if our chickens free range are pretty unnecessary really, as they'll just ignore stuff which wouldn't be good for them, assuming they had plenty of more suitable food available.