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What is Snow on the Mountain?

Of the genus Euphorbia, snow-on-the-mountain (scientific name Euphorbia marginata Pursh), is a summer annual originating in North America. It has alternate leaves where the upper leaves have a white margin and there are clusters of flowers. The flowers of the plant are white and cup-shaped and the plant has a milky sap. 

Snow-on-the-mountain grows in dry, hot environments, in the sun or partial shade, with clay-like soils. The plant will be found in pastures and rights-of-way, as well as in piles of trash. The plant can grow to two to three feet in height. All parts of the plant are poisonous, whether fresh or dried.

Snow-on-the-mountain, or Euphorbia marginata, is a summer annual with alternate leaves and white cup-shaped flowers, all parts of which can be poisonous in horses.

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Symptoms of Snow on the Mountain in Horses

Should your horse consume snow-on-the-mountain he may experience blistering, irritation and inflammation of the mouth, throat and esophagus. Any contact with the plant can lead to irritation of the eyes, skin and mucous membranes. The sap has been found to cause contact dermatitis on a horse’s legs and face. 

  • Nausea
  • Diarrhea
  • Irritation of the mouth, throat and esophagus
  • Blistering of the mouth, throat and esophagus
  • Skin, eye and mucous membrane irritation
  • Dermatitis


Other plants from the genus Euphorbia include:

Euphorbia cyparissias L (Cypress spurge) - A colonial plant with linear leaves that is yellowish green when young and then turns purplish red; the plant can cause diarrhea, collapse and even death; hay can be contaminated with this.

Euphorbia maculata L (Wartweed) - These plants grow like mats over the ground in the pasture  with leaves at the base that are dark green and elliptical; it is thought that toxicity increases in July and August when rains follow a drought.

Causes of Snow on the Mountain in Horses

All parts of the plant are poisonous, though the sap is the most toxic. When the plant is dried it will still contain poisonous properties. Poison includes volatile oils, resins, alkaloids, diterpene esters and glycosides. When consumed, this plant will cause a low level of toxicity in your horse. Should skin irritation occur, it will last for a few minutes.

How sensitive your horse is to the toxin will vary based on his age, weight, physical health and how susceptible he is. Toxicity in the plant can vary based on the season, the part of the plant ingested, and its stage of growth. Plants are also able to soak up toxic substances (herbicides, pesticides, and pollutants) that are present in the water, air and soil.

Diagnosis of Snow on the Mountain in Horses

Should you notice unusual symptoms in your horse, it is a good idea to contact your veterinarian. If you saw your horse ingest snow-on-the-mountain, show the veterinarian the plant so he may identify it on your property, as this may help your veterinarian make a diagnosis. If you did not see your horse consume snow-on-the-mountain, but suspect he is experiencing poisoning, you will want to produce a sample from any plants that may be responsible for the poisoning.

Your veterinarian will ask you for information regarding the symptoms you have seen, when you first noticed them and any changes that have occurred. A full examination of your horse will be conducted. Depending on what your veterinarian sees during the evaluation, as well as whether you saw your horse ingest snow-on-the-mountain, he may administer further testing, to include a complete blood count, in order to rule out other possible causes of his symptoms.

Treatment of Snow on the Mountain in Horses

Toxicity from snow-on-the-mountain is self-limiting. Depending on the severity of the symptoms, your veterinarian might provide supportive care for your horse. This could include fluids in the case of dehydration, medication for pain produced by blistering, and ointment for the dermatitis. Providing nutritious feed is important and you will want to be sure that your horse no longer has access to snow-on-the-mountain in the areas where he spends time.

Recovery of Snow on the Mountain in Horses

Should your horse experience toxicity from snow-on-the-mountain, you will want to follow the recommendations of your veterinarian to ensure the best outcome for him. Providing good quality pasture space and hay will be helpful in his recovery. It will be important that you survey the areas he has access to in order to be sure that there is no snow-on-the-mountain or other toxic plants present so that he can avoid future toxicity.