Very wise words, Heather -- thanks!
And you are right that many horses, and most cattle, shy away from Ragwort in fields. The toxic component -- pyrrolizidine alkaloids -- give the plant a very bitter taste when it is fresh, but the process of wilting or dying reduces the bitterness and, as you say, when it is mixed with hay it is very difficult to taste. Here's an article from a Dutch Ragwort website about how the toxins in Ragwort work:
http://www.ragwort.org.uk/component/con ... es-it-work
And here is another article from a UK site that says that although Ragwort is indeed deadly, the numbers of actual deaths of horses has been exaggerated:
http://www.ragwortfacts.com/ragwort-horse-deaths.html
That doesn't lessen the fact that it is deadly, and its effects are cumulative and so might not be seen until it is too late. So your advice to respect it, and certainly to dig it up and not let it set seed is excellent advice, and I hope that people follow it.
One of the real problems that we have when we are researching individual plants as potential food for tortoises is that the digestive system of reptiles is different from that of mammals, and it is well known that many tortoises inhabit areas where food is scarce, and so in order to compete with mammals for the little food available, some species of tortoise have evolved to be able to eat plants that would otherwise be toxic to mammals. Unfortunately, most scientific research is undertaken with reference to either humans, or livestock, and in a few cases pets like cats and dogs. So we have to interpret the conclusions of research on particular plants where reptiles were not a part of the study. For this reason, and because we are dealing with people's precious pets, we always err on the side of caution, but with Ragwort I think there is no grey area -- I would never risk my tortoise coming into contact with it.
Nina