I haven't fed it to the chooks, isn't it slightly hairy? If so, I would have thought that naturally they would ignore it, my observations on the range have been that they love either 'juicy' things like sorrel or seedheads. However, you can make comfrey tea which is very good as an organic fertiliser, albeit a bit stinky during the making. My previous garden was full of the stuff, its quite rampant. I believe you can also make a different sort of comfrey tea for humans!