Ragwort and meat some expert opinions
It is often claimed that ragwort being eaten by animals makes the meat poisonous to people. This is not so. This page provides the data to show the truth of the matter.
The following is a quote taken from another website, the reference to which is below. It is by by Dr Peter Cheeke of Animal Sciences Department Oregon State University a leading researcher into Ragwort. In the USA ragwort has become a problem because like many species released into a foreign ecology it is not controlled by its natural predators and diseases. This is not the case in the UK where it is a native and natural part of the ecosystem.
The PA [ pyrrolizidine alkaloids] are not accumulated in the tissues; it is the damage that is cumulative. The damage is confined to the liver, which in an animal with ragwort toxicity would be shrunken and fibrotic. The carcass would likely be condemned because of the liver damage. In sheep which had consumed ragwort but did not show obvious liver damage, there would be no residues of PA in the meat. The PA are metabolized in the liver, and excreted as conjugates in the urine. Small amounts of pyrrole bound to DNA in the liver would not be measurable. Thus in my judgement there is no concern whatsoever about possible human toxicity from consumption of meat from sheep which had consumed ragwort.
Another source of information on this subject comes from a standard text book Chemistry and Toxicology of Pyrrolizidine Alkaloids which is written by Dr A. R. Mattocks of the Toxicology unit in the UK's Medical Research Council Laboratories
There is no record of PAs being detected in meat products from livestock which might have ingested PAs. Past experience with laboratory animals suggest that levels of PAs in the tissues fall very rapidly after intake. Metabolism by liver enzymes is fast, at least in the rat, and toxic metabolites are quickly deactivated. During the chronic ingestion of PAs the effects of the alkaloids are cumulative in the liver but the alkaloids themselves are not. Thus we anticipate that concentrations of Pas in tissues would only be be high is the animals were killed very soon after a massive intake.