Amsinkia intermerdia – Common Name: Tarweed & Fiddleneck
A common weed in the desert southwest is showing up in large volumes this year and causing liver disease in horses & livestock.
What is it?
A substance in the plant that is converted to a toxin called pyrroles in the body. This toxin can bind to DNA in liver cells and percent them from undergoing cellular division and liver regeneration. This process will continue as more & more of the weed is ingested until in a few weeks the once healthy liver cells are replaced by scar tissue (fibrosis) and the liver is unable to complete its normal functions resulting in liver failure. Other tissues are affected in the horse in smaller amounts including the heart muscle and the lungs.
Does it taste good?
Not really, typically horses on poor or limited pastures are the ones exposed to this toxin. As the pasture is overgrazed only these hardy weeds grow and the horses will then graze on and ingest this plant.
How Toxic is it?
Very, as little as 15mg/kg in a horse over as few as 2 weeks can potentially cause liver failure. Other estimates of toxic dose are between 1 & 5 percent of body weight ingested daily for 2 weeks.
So how do I know if my horse has liver problems?
Easy answer – Have you vet examine and run a blood panel on your horse. Blood work should include at a minimum a CBC and a chemistry panel. The blood panel can pick of signs of toxicity prior to your horse being in full liver failure – giving you time for corrective action. Your doctor will look for common signs of liver failure including icterus (yellowing of mucus membranes & skin), unexplained hemorrhage, abnormal behavior, weight loss and a poor appetite. Some horses may also develop sensitivity to sunlight causing dermatitis.
The only definitive diagnosis is a liver biopsy but many veterinarians will formulate a tentative diagnosis based on history of the weed in the horse’s pasture and both laboratory and clinical signs.
What is the antidote?
Answer – none, the treatment consists of supportive care and early diagnosis of disease with elimination of the weed form the feed or pasture. Commonly skin wounds are treated, fluid support is given and basically the horse is kept alive giving time for the liver to make new cells (regenerate) and heal. Thus the importance of early action in removal of this plant for the horse’s graze cannot be overstated.
Please consult with your equine veterinarian for assistance with your particular horse. Most veterinarians are more then happy to review your feeding and pasture management system to prevent a problem. Also regular interaction with you veterinarian will enable disease to be caught and corrected early, potentially saving your horse.