Fiddleneck Poisoning in Horses

The name fiddleneck refers to a group of plants in the Amsinckia genus that have a distinct curled stem adorned with brightly colored flowers, usually in orange or yellow. These plants contain pyrrolizidine alkaloids, which are hepatotoxic in large amounts. Although the plant is common, poisonings are relatively rare due to the unpalatability of the weed. Those horses that do develop symptoms of poisoning usually have irreversible liver damage, but if caught early, management techniques may improve and extend the animal’s life.

The flowering weed fiddleneck contains dangerous levels of pyrrolizidine alkaloids, which can cause severe liver damage to horses when it is consumed in large amounts.

Fiddleneck poisoning damages the liver when it is eaten in large quantities. Although it is possible to develop symptoms from a single substantial serving, in most cases this occurs over several feedings. In a significant number of animals, the signs of liver damage take several months after exposure to develop.

• Aimless wandering
• Blindness
• Circling
• Dermatitis 
• Head pressing
• Jaundice
• Lack of coordination
• Loss of appetite
• Photosensitivity
• Seizures
• Swollen limbs
• Weakness
• Weight Loss 

Types 

There are several types of fiddleneck that contain the pyrrolizidine alkaloids that cause the  poisoning in horses. Some of the more common or notable varieties include: 

• Bristly fiddleneck (Amsinckia tessellata) - Native to much of the western side of North America, this plant is also commonly known as devil’s lettuce
• Coast fiddleneck (Amsinckia spectabilis) - Also known as seaside fiddleneck, this yellow flowered fiddleneck is often found throughout the Pacific coast of North America
• Large-flowered fiddleneck (Amsinckia grandiflora) - A critically endangered variety of fiddleneck with particularly large flowers. There are less than 500 individual plants left, found only in California
• Malheur fiddleneck (Amsinckia carinata)- An imperiled variety of fiddleneck found only in Oregon. This type of fiddleneck believed to be extinct as of 1896, but it was rediscovered in 1984
• Menzies’ fiddleneck (Amsinckia menziesii)- An orange or yellow-orange flowered fiddleneck that is found in abundance throughout North America as well as in Australia that is also known as common fiddleneck and rancher’s fireweed
• Tarweed fiddleneck (Amsinckia lycopsoides) - A common yellow-flowered fiddleneck that is found throughout North America and in Australia

Fiddleneck plants contain pyrrolizidine alkaloids which, when metabolized in the liver, become cytotoxic, causing irreversible liver damage. This usually only occurs after large amounts of the toxin have been ingested, usually over several weeks or months. Fortunately, the plant is generally avoided by horses as they are unpalatable. This makes poisonings rare, only occurring during drought conditions or when feed becomes contaminated.

The proper recognition of the plant either in the pasture or in the feed will get a preliminary analysis. Your veterinarian will try to gather as much information regarding the amount of plant material that was ingested and how long it has been since it was eaten as possible. They will also need to get a comprehensive history of the animal in question, which will provide as much knowledge as possible about the horse’s medications, diet, and environmental elements. 

Standard blood tests, including a complete blood count and biochemistry profile, will need to be evaluated to see if any infections are present as well as establishing the levels of liver and kidney enzymes found in the blood. These tests are likely to show high levels of liver metabolites and enzymes. Your veterinarian will usually recommend an ultrasound of the abdomen to see the current shape and size of the organ, and a biopsy of the tissues will help to identify the fibroids indicative of liver damage due to pyrrolizidine alkaloids, as well as assisting with locating where in the liver the damage is and estimating how progressed the disease is.

If the consumption of large quantities of fiddleneck plants was recent, then your horse’s doctor may choose to perform a gastric irrigation procedure in order to remove as much of the toxic material from the digestive system as possible. It is also standard to administer activated charcoal in these situations, as it can prevent further absorption of the pyrrolizidine alkaloids into the bloodstream. Most poisonings by the fiddleneck plant are chronic in nature, however, and by the time symptoms have emerged, irreversible liver damage has already occurred. 

Initial supportive treatments that are frequently employed include IV fluids to prevent dehydration and combinations of electrolytes and sugars in order to adjust for any imbalances that may have developed. Although the damage to the liver is not reversible, it can sometimes be moderated by switching to a low-protein diet with added vitamins and potassium. Medications to reduce the amount of ammonia in the gut can also be helpful in slowing the disease as reducing the ammonia levels can also decrease the workload for the liver.

The prognosis for horses who have been poisoned by eating plants that contain pyrrolizidine alkaloids, such as fiddlenecks, is poor to guarded as significant damage to the liver is usually present by the time the symptoms have become apparent. This particular disorder typically causes scarring in the form of fibroids to develop within the liver, preventing both healing and regrowth. The higher the amount of the fibroid tissue in the liver, the poorer the prognosis. In cases where the amount of damage to the horse’s liver function is extensive, or when extreme symptoms are manifesting, veterinarians may suggest euthanasia in order to prevent prolonged suffering.