Buttercup poisoning in horses occurs when they ingest protoanemonin, a toxin produced by the buttercup plant. Although relatively rare, the ingestion of this flowering weed results in irritation to the horse’s mouth and digestive tract. [1]

Horses with buttercup toxicity may develop red, swollen lips and gums, oral and stomach ulcers, decreased appetite, colic, and diarrhea. [2][3]

Diagnosing buttercup poisoning in horses can be challenging due to the absence of specific diagnostic tests. Diagnosis usually involves a detailed history and physical examination, along with ruling out other causes of disease. [2][4]

The prognosis for horses with buttercup poisoning is generally good. Treatment involves relocating horses away pastures infested with buttercup plants and providing supportive care for those with severe symptoms. [3][4][5]

Buttercup Poisoning in Horses

Buttercups are flowering plants belonging to the Ranunculus family, with green leaves divided into three lobes. These plants are easily recognizable by their five bright yellow petals, which sit atop thin, upright, and smooth stems. [1][4]

In North America, several species of buttercups are prevalent. The most common species is the bur buttercup (Ranunculus testiculatus, also known as Ceratocephalus testiculatus), while the bulbous buttercup (Ranunculus bulbosus L) thrives in cooler, wetter climates.

Other notable species include the tall buttercup (Ranunculus acris) and the smallflower buttercup (Ranunculus abortivus). [2][3][5]

Buttercup Poisoning in Horses | Mad Barn USA

Originally from Europe, the buttercup weed has spread extensively and is now a common sight in the pastures of Canada and the United States. It thrives in over-grazed pastures and in wet, poorly drained soils. [1][3][5]

Effects on Horses

Buttercup leaves, stems and flowers are toxic to horses because they contain a chemical called ranunculin. When the plant is chewed, ranunculin transforms into protoanemonin, a bitter compound that causes irritation and inflammation to the skin and oral cavity. [1][4][9]

Once digested, protoanemonin is metabolized into a less toxic chemical called anemonin. Despite its reduced toxicity, anemonin can still induce symptoms as it passes through the remainder of the gastrointestinal tract. [5][9]

Compounds in buttercup plants may also adversely affect the beneficial microflora in the hindgut of horses. [5]

Toxicity

The highest levels of ranunculin are found in the buttercup plant during its flowering stage. Once the plant dries, the toxicity significantly decreases and pose less concern to horses. [2][3][4][9]

The exact amount of buttercups required to cause toxic effects in horses is unknown. Furthermore, toxin concentrations differ among various buttercup species, affecting the amount required to produce adverse effects.

In sheep, it has been estimated that the consumption of approximately 500 grams of buttercups can be lethal. Another method to assess the risk of toxicity to horses is by determining the pasture’s plant coverage; a pasture with 30% buttercup coverage is potentially toxic to horses. [5][8]

Prevalence

While buttercup poisoning in horses is rare, the exact prevalence of such poisoning incidents is unknown. [3][4][6][7]

There is some evidence suggesting that outbreaks of equine grass sickness (equine dysautonomia) in Great Britain may be linked to a higher occurrence of buttercup plants in the area. [7]

Risk factors

Environmental factors, such as drought, use of fertilizers, and soil mineral levels, can influence the levels of toxins in plants. These factors can lead to fluctuations in the toxicity of plants from one year to the next. [4]

Lactating mares and foals appear to be more susceptible to buttercup intoxication. Affected foals have a higher risk of experiencing severe weight loss, diarrhea, and dehydration, along with serious neurological signs. In extreme cases, these complications can lead to fatalities or necessitate euthanasia. [5]

Clinical Signs

Common symptoms observed in horses that have ingested buttercup plants include: [24][9]

The severity of clinical signs usually depends on the amount of plant consumed. [4] In very rare cases, fatalities have occurred. [9] Buttercups poisoning has also been associated with abortion in pregnant mares. [5]

Horses that consume buttercups over a long duration can experience severe weight loss due to prolonged watery diarrhea. [1]

Neurologic Signs

Some species of Ranunculus are capable of producing additional neurologic signs. Affected horses may exhibit signs including: [2][3][9]

  • Incoordination
  • Blindness
  • Recumbency
  • Seizures
  • Tremors
  • Paralysis
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Diagnosis

Diagnosing buttercup poisoning is challenging due to the absence of specific tests or distinct disease markers. If you suspect your horse has ingested buttercups plants, consult with your veterinarian to obtain a proper diagnosis. [4]

Your veterinarian will diagnose buttercup poisoning by conducting a thorough history, patient examination, and pasture and feed examination. Additionally, ruling out other genetic, infectious, nutritional, and toxic diseases is crucial. [2][4]

History and Physical Examination

In cases of buttercup poisoning, it is common for several or all horses on the same pasture to be affected. The outbreak of clinical signs in multiple horses at the same time is key to ruling out more common diseases that impact individual horses, such as endocrine or dental diseases. [5][10]

While affected horses can display a variety of symptoms, the presence of oral lesions combined with other clinical signs in a herd can help narrow down the list of possible causes. [11]

Environmental and feed-related factors, such as recent feed changes, moving to a new location, weather variations, and the abundance and coverage of plants in the pasture, can also provide valuable insights as part of the history. [11]

If symptoms subside after horses are relocated to a pasture free of buttercups, this further strengthens the likelihood of buttercup poisoning as the diagnosis. [5]

Diagnostic Testing

There are no tests available to detect the toxin from buttercups in a horse’s system. However, diagnostic tests including bloodwork, bacterial culture, urinalysis, and fecal analyses may still be recommended to rule out other causes. [5][11]

If toxicity is suspected, examining both the horse’s water and food is crucial. Testing can be conducted on samples of hay, grains, concentrated feeds, supplements, water, and pasture soil to detect toxins. Additionally, plants from the pasture should be collected for identification and testing of potential toxins. [5][11]

Tests to detect other plant toxins in the horse’s system might be recommended to rule out common toxicities that share similar clinical signs.

Despite their bitter flavor, horses still consume buttercups even when provided with alternative grains and hay. The presence of buttercups in a pasture, combined with clinical signs that are consistent with buttercup poisoning, also supports the diagnosis. [2][5]

Post-Mortem Examination

Diagnosing buttercup toxicity in horses post-mortem is difficult, as findings are non-specific. In horses that were euthanized or died due to buttercup poisoning, ulcers are found throughout their gastrointestinal system.

Other findings include redness in the digestive system and manure ranging from poorly formed to liquid consistency. In severe cases, blood is discovered in the abdominal cavity. [1][5][6]

Identifying buttercup plants in the stomach can be challenging once they have been chewed and partially digested. However, the presence of plant material in the stomach may still support a diagnosis. [4][5][6]

Differential Diagnoses

Since buttercup poisoning in horses is rare, other potential causes of disease must be ruled out before confirming a diagnosis.

Infectious Diseases

Certain infectious bacteria and viruses, such as Salmonella, Clostridium perfringens, Clostridium difficile, Neorickettsia risticii, and coronavirus can produce gastrointestinal signs similar to those of buttercup poisoning, including decreased appetite, colic, and diarrhea.

These infections should be ruled out as potential causes before making a diagnosis, particularly if multiple horses on the farm are affected. [11]

NSAID Toxicity

Non-steroidal anti-inflammatory drugs (NSAIDs) are used to treat pain and inflammation in horses. However, long-term use or accidental overdose of NSAIDs can result in toxic effects.

Improper use of oral NSAIDs can cause ulcers in the mouth and gastrointestinal tract, producing similar clinical signs as buttercup poisoning. [11] The risk of toxicity for different NSAIDs varies, with phenylbutazone being more likely to cause a toxic event compared to flunixin meglumine. [11]

Other Plant Toxicities

Several plants can cause clinical signs in horses that are similar to those caused by buttercup poisoning. Examples include the following plants in the Ranunculus family that also contain protoanemonin: [4]

  • Hellebore
  • Marsh marigold
  • Clematis
  • Anemone

Other plants can cause physical trauma to the oral cavity when ingested by horses, often resulting in drooling. Such plants include: [4]

  • Bristle grass (Setatia species)
  • Wheat (Triticum aestivum)
  • Rye (Secale cereale)
  • Bristles of burdocks (Arctium species)

Additional poisonous plants can cause excessive salivation, colic, and diarrhea in affected horses. These include: [2][4]

  • Laurel (Kalmia species)
  • Rhododendrons and azaleas (Rhododendron species)
  • Foxtail barley (Hordeum jubatum)
  • Halogeton (Halogeton glomeratus)
  • Greesewood (Sarcobatus vermiculatus)
  • Shamrock, Soursob, or sorrel (Oxalis species)
  • Nightshades (Solanum species)

Treatment

The first step in treatment is to remove all horses from pastures infested with buttercups. Horses affected by buttercup poisoning typically recover quickly once exposure to the toxic plants is eliminated. [1][3][5]

In severe cases, additional supportive care may be necessary to manage colic, pain and/or diarrhea. Potential treatments include: [3][4]

Prognosis

The prognosis for horses experiencing weight loss and other mild clinical signs is favorable. Weight loss typically resolves within 2 months after the horses are moved to a pasture free of buttercups. [5]

Mares that have suffered abortion due to buttercup toxicosis can still have a successful breeding career in subsequent years. [5]

Prevention

The best way to prevent buttercup poisoning is to maintain healthy, dense pastures and remove buttercup plants. Regularly inspect pastures to identify buttercup flowers or other poisonous plants.

If a particular area of a pasture is heavily infested with buttercups, restrict horses’ access to this area, especially during the peak flowering season of the plant.

Pasture Management

Horses typically need to consume a large amount of buttercups over a prolonged period, often weeks to months, to experience negative consequences. It is estimated that horses would need to ingest about 5-10% of their body weight in buttercups to be negatively impacted.

Therefore, if a pasture has only a few buttercups and plenty of other, more nutritious forage options, the risk posed by the plant is generally low. [4]

Buttercups thrive in over-grazed areas and in wet, poorly drained soils. Preventing overgrazing in pastures as well as improving soil drainage may help prevent the overgrowth of buttercups. [3][5]

Other ways to promote healthy forage and minimize the over-proliferation of buttercups is by fertilizing the pasture and overseeding. [5] Learn more in our guide to maintaining healthy pastures for horses.

Herbicides

Herbicides can be used to target the elimination of buttercup flowers in pastures. It’s crucial to restrict grazing on these pastures during herbicide application due to their potential toxic effects.

However, if buttercups are not eradicated and horses selectively consume other grasses, the weed may proliferate and overrun the pasture. [3][5]

Vaccines

No vaccines are available to prevent buttercup poisoning. Nevertheless, keeping horses up to date with their annual vaccinations for other infectious diseases is important and can help rule them out as potential differential diagnoses. [5]

Summary

  • Buttercup is a common flowering weed that is toxic to horses. Ingestion of this plant can irritate membranes in the mouth and stomach, leading to symptoms such as drooling, redness of the lips and gums, and colic. [1][4]
  • The fresh leaves and flowers of the buttercup contain ranunculin, which is converted into a toxin upon being chewed and ingested by horses. This toxin, called protoanemonin, is released when the plant’s cells are damaged. [9]
  • Symptoms and diagnostic tests for buttercup poisoning are not specific to the condition. Diagnosis typically depends on ruling out other potential causes of the disease or identifying the plant in pastures. [2][4][11]
  • Treatment of buttercup toxicity involves relocating horses to a pasture free of these plants. Horses usually experience resolution of clinical signs within two weeks of being relocated. [3][5]
  • To prevent buttercup poisoning, implement effective pasture management strategies and prevent overgrazing. [3][5]

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References

  1. Colorado State University, Guide to Poisonous Plants – Buttercup, crowsfoot. College of Veterinary Medicine and Biomedical Sciences – Colorado State University. Accessed Jan. 04, 2024.
  2. Stegelmeier B.L. and Davis T.Z., Toxic Causes of Intestinal Disease in Horses. Veterinary Clinics of North America: Equine Practice. 2018. View Summary
  3. Martinson K. et al., Plants Poisonous or Harmful to Horses in the North Central United States. University of Minnesota Extension. 2007.
  4. Knight A.P., Poisonous plants. In: Nutritional Management of Equine Diseases and Special Cases. John Wiley & Sons, Ltd. 2017.
  5. Swerczek T.W., Abortions in Thoroughbred Mares Associated with Consumption of Bulbosus Buttercups (Ranunculus Bulbosus L). Journal of the American Veterinary Medical Association. 2016. View Summary
  6. Griess D. et al., Diagnosis of Acute Poisoning by Ranunculi (Ranunculus Acris L and Ficaria Ranunculoides L) in Horses. Revue de Medecine Veterinaire. 1997.
  7. Michl J. et al., Metabolomic Analysis of Ranunculus Spp. as Potential Agents Involved in the Etiology of Equine Grass Sickness. J Agric Food Chem. 2011.View Summary
  8. Olsen J.D. et al., Bur Buttercup Poisoning of Sheep. J Am Vet Med Assoc. 1983.
  9. Khan R.U. et al., Toxic Effect of Common Poisonous Plants of District Bannu. Pakistan journal of pharmaceutical sciences. 2018.
  10. Lavoie J.-P. and Hinchcliff K.W., Blackwell’s five-minute veterinary consult: equine. 3nd ed. Wiley-Blackwell. 2019.
  11. Lynn R Hovada et al., Blackwell’s Five-Minute Veterinary Consult Clinical Companion: Equine Toxicology. Wiley & Sons, Inc. 2022.