Most dogs will grab a chicken. It's up to the owner to make sure he can't get to them. My dog who died last year was never allowed access to the birds because I knew he would go on a killing spree. The dogs were fenced, as they always are when we have them. The birds are penned and would freerange daily, but they never had access to the dogs' area. It's just something you have to be vigilant about. Never assume a dog won't kill a chicken under the right circumstances.