There seems to be some articles on the web for this issue - I was investigating this some time ago and found this:
Information on Ragwort in the UK from a scientific perspective
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Professor M.J. Crawley FRS, at...
Have just got into riding and just met a wonderful guy but non-horsey. I'm afraid that I will have to choose between one and the other because he has no interest in horses and I cannot imagine anything working in the long term because of this issue.
Have you had the same dilemna? What did you do?