my back "woods" as my boys call it-- really, it's just some trees-- is full of poison ivy. Is it going to harm my chickens? I had 3 hens out there last fall, but this summer, I'll have about 28 pullets wandering through the trees. will they eat the poison ivy? if they do, is it ok? is there a good way to get rid of it that is safe for my girls (if them eating it is not)?