Question: are all sycamore trees poisonous to horses?
Answer: Sycamore tree poisoning, if not treated promptly by a veterinarian, can be fatal to the horse. The seeds and seedlings of the sycamore tree contain the toxic agent hypoglycin A, which causes severe muscle damage. If a horse ingests the seeds or seedlings of a sycamore tree he will develop atypical myopathy.