Thanks again. There is no rhode plants or related plants we can see, have hunted under bushes etc, goats licks are only put in their house at night and taken out in the morning so they have no access to them and we have been super careful in the feeding as the NRs get different food. We ruled out the rhubarb as it is almost definately caterpillar/slug munching. We will keep looking today. Not into cutting open animals I'm afraid, there is a place fairly near which does autopsy but I am sure they need the carcas to be 'fresh' and as its bank holiday weekend we may have to rule that one out.
Thanks you all, its great to have words of comfort from you, really is.