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 Canada

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]


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]


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
  • <