Amsinckia Species Poisoning in Horses

Amsinckia Species Poisoning in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

Most common symptoms

Diarrhea / Increased thirst / Lethargy / Poor Appetite / Shaking / Weakness


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Most common symptoms

Diarrhea / Increased thirst / Lethargy / Poor Appetite / Shaking / Weakness

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Amsinckia Species Poisoning in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

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What is Amsinckia Species Poisoning?

Members of the Boraginaceae family, fiddlenecks can be found throughout North America in fields, roadsides, pastures, grasslands, and waste areas, as well as cultivated areas such as orchards, vineyards, and within crops. They can be perennials or annuals, and are characterized by their flowering heads that curl like a fiddle neck. The yellow flowers are seen from late winter to spring. Fiddleneck stems can reach 4 feet in height, with alternate, lance-shaped leaves. Fruit consisting of four nutlets separate after dispersal to release the seeds which germinate from fall to early spring.

Plants in the Amsinckia species are better known as fiddlenecks. Horses affected show symptoms relating to liver damage and failure, though signs can appear a long time after the plant was ingested. Most often, horses are chronically poisoned with small amounts over a length of time. Timely treatment is needed, as this poisoning can be fatal.

Symptoms of Amsinckia Species Poisoning in Horses

Symptoms of a chronic fiddleneck poisoning may not be seen until several weeks or months after the first ingestion of the plant has taken place, and may appear even if consumption has ceased. Signs in your horse generally reflect a progressive and irreversible liver disease. Acute toxicity can occur with larger doses, but horses are often found dead from internal hemorrhaging before other signs are noticed. Symptoms include:

  • Loss of appetite 
  • Depression
  • Colic
  • Jaundice
  • Diarrhea
  • Constipation 
  • Bloody feces
  • Weight loss
  • Photosensitivity
  • Loss of condition
  • Dullness
  • Abdominal swelling
  • Behavioral changes
  • Weakness 
  • Yawning
  • Head pressing
  • Incoordination
  • Wandering aimlessly, known as walk-about disease
  • Awkward gait
  • Pushing against fences
  • Biting the ground
  • Aggressive or frenzied behavior 
  • Reluctance to move 
  • Lying down
  • Pica 
  • Difficulty breathing
  • Pneumonia 
  • Coma 
  • Liver failure
  • Sudden death

Additional symptoms seen when fiddlenecks contain a high concentrations of nitrates include:

  • Abortions and other fetal issues
  • Reduction in milk production
  • Vitamin A deficiency
  • Weak, rapid heart rate
  • Lowered body temperature
  • Muscle tremors
  • Loss of bodily control
  • Brown mucous membranes
  • Increased urination


There are many types of fiddlenecks in the Amsinckia species. Some of the more common ones seen include:

  • Menzies fiddleneck, Amsinckia menziesii
  • Coast fiddleneck, Amsinckia intermedia 
  • Tarweed, Amsinckia lycopsoides
  • Common fiddleneck, Amsinckia douglasiana

Causes of Amsinckia Species Poisoning in Horses

The cause of poisoning by ingestion of fiddlenecks is due to the pyrrolizidine alkaloids they contain. These alkaloids alter DNA strands in target sites of the body, including the liver, kidneys, and lungs, causing abnormally large red blood cells, an arrest of cell division, and other toxic effects on cells. Fiddlenecks can also contain nitrates, which can affect reproduction and fetal growth, and the respiratory and nervous systems. 

Plants in the Amsinckia species are not very palatable, which makes an acute poisoning rare. Chronic poisoning is more often seen due to contamination of hay or feed, or in certain situations where there is not a better food source available, such as drought or an overgrazed pasture. While the exact amount that causes a toxicity is not known, it is estimated that consumption of 5% to 10% of your horse’s body weight can cause a serious toxic reaction.

Diagnosis of Amsinckia Species Poisoning in Horses

A poisoning due to ingestion of an Amsinckia plant can be difficult, as often symptoms do not appear until long after ingestion has occurred. If you have seen your horse eat fiddlenecks, a diagnosis can be based on evidence of exposure and any symptoms you do see. Since the symptoms can be delayed, owners often do not connect fiddlenecks with clinical signs, causing your veterinarian to run several tests to narrow down a cause.

Blood and serum tests, including an ELISA, spectrophotometry, and gas chromatography/mass spectrometry, along with a urinalysis, are often performed along with a physical exam. These tests can often reveal the presence of pyrrolizidine alkaloids and nitrates, which can lead to a diagnosis of a plant poisoning. Enzyme levels in the serum can also detect liver damage. A liver biopsy may then be performed for further testing.


Treatment of Amsinckia Species Poisoning in Horses

There is no antidote or specific remedy for this type of plant poisoning. Treatment is symptomatic and supportive. Remove fiddlenecks from your horse’s reach to prevent continued exposure. Fluid and electrolyte therapy may be given in cases of dehydration. Treatments for photosensitization can be prescribed, which can include keeping your horse out of sunlight, including topical creams and lotions. 

Your horse’s diet may be altered to include a higher amount of carbohydrates. In cases of a nitrate toxicity, injections of isotonic saline or methylene blue may be given, along with a cold water lavage and antibiotics.

Recovery of Amsinckia Species Poisoning in Horses

Once symptoms appear in your horse, recovery is rare as it often means that irreversible liver damage has already occurred. Horses can be found dead before a diagnosis can be made. Due to the ability of the liver to regenerate, your horse may recover if treatment is begun in time, and fiddlenecks are removed from the diet.

Amsinckia poisoning can be lethal, making prevention the best way to ensure your horse is not affected. Remove fiddlenecks from your property, fence lines and trails by hand pulling, mowing, and tilling in cultivated areas. Herbicides can also be used successfully before seeds are produced.

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Amsinckia Species Poisoning Questions and Advice from Veterinary Professionals