Ragwort Toxicity

Description

Ragwort (Senecio jacobea) is part of the daisy family, a flowering plant with completely yellow flowerheads. It commonly grows on wasteland and grazing pastures. It is poisonous to livestock with Horses and cattle being more susceptible than sheep. When ingested over long periods of time it causes hepatotoxicity which in the severe form is invariably fatal. Exposure to the toxin is usually via ingestion of contaminated hay or silage as the animal will avoid it in the fresh form.

The toxin is a pyrrolizidine alkaloid.

Diagnosis

Clinical signs

• Weight loss
• Hepatic insufficiency
• Hepatic encephalopathy

References

• Knottenbelt, D.C. A Handbook of Equine Medicine for Final Year Students University of Liverpool
• Rose, R. J. and Hodgson, D. R. (2000) Manual of Equine Practice (Second Edition) Sauders.

Hepatotoxicity

• • livestock will not normally eat the fresh plant
  • most cases arise in horses and cattle consuming ragwort in hay or silage
• pyrrolizidine alkaloids
  • toxic principle converted in the body to the toxic intermediate pyrroles and their esters
  • cause intitial and continued damage to hepatocytes
  • have an anti-mitotic effect whilst allowing continued synthesis within the cell and its nucleus
    • causes a marked increase in the size of parenchymal cells, a phenomenon termed 'megalocytosis'
    • these very enlarged hepatocytes can be up to 20 times bigger
    • the enlarged cells are closely apposed so that the sinusoids may not be evident
• it is likely that the vascular component of the attempted repair of the chronic damage by fibrosis (really a type of granulation tissue) aids the shunting from the portal triads to the central vein and thereby bypassing the hepatocytes
• other plant and fungal toxins perform in the same way

Gross

• slightly enlarged liver
• pale in colour
• very firm to section

Microscopically

• necrosis
• haemorrhage
• diffuse fibrosis

Also known as:

Senecio jacobea