Ragwort (Jacobaea vulgaris
or Senecio jacobaea
) is a biennial (sometimes annual or perennial) herbaceous flowering plant.
It is considered an invasive weed in most parts of the world and is well known for its poisonous effects on livestock over the years. It is recognized by its daisy-like yellow flowers, which contain 13 petals. Ragwort has erect, unbranched stems that grow up to 4 feet in height and branch near their tips. As a biennial, tansy ragwort spends the first year in the rosette stage with dark green basal leaves that appear ruffled. During the second year, one or two flowering stems form.
Horses are particularly sensitive to the poisonous effects of ragwort, and tend to avoid it; however if horses are turned out in pastures with no available forage or if provided hay contaminated with ragwort, they are more likely to ingest it. Ragwort contains pyrrolizidine alkaloids (jacobine, eruifoline, and senecionine) which causes pyrrolizidine alkaloid toxicity
, often leading to liver failure when consumed over a prolonged period of time. Unfortunately, clinical signs take a while to show, which is usually after liver damage is advanced and irreversible.