OK, does anyone know how poisonous this plant is to chickens and ducks? And symptoms etc. too. I would prefer personal knowledge since when I looked it up on the internet it said that it was highly toxic to horses, and it isn't really. You have to watch the horses, but the first sign of too much horsetail with horses is a cough. Then you can feed them brewers yeast, or if it is very bad a vitamin K injection, and they are fine. I wanted to know exactly how it works with chickens since I have a mysteriously ill rooster right now....the only thing I can think of is that he got some horsetail in the weeds I toss to them. He is eating and drinking, but he can't stand up. It is the oddest thing.