What is Wild Parsnip Poisoning?
Wild parsnip is a biennial flowered plant found throughout the United States. It can grow up to 6 feet tall, and produce umbrella shaped yellow or red tinged yellow flowers. Its leaves have saw toothed edges and the stem is a bit hairy and grooved. This weed resembles Queen Anne’s lace, and can be found in pastures and fields, and along roadsides and ditches. It is toxic to many species, including people, when ingested fresh or dried, and can even cause a skin reaction when touched.
Wild Parsnip, or Pastinaca sativa L., is a weed that is not in the normal diet of horses. In situations where forage has been overgrazed, or wild parsnip has been accidentally baled into hay, horses will eat it. The toxins in wild parsnip affect the skin by causing a reaction when exposed to sunlight. The resultant sunburn can be severe, and a source of pain and discomfort for your horse that will continue until exposure to UV radiation and wild parsnip is eliminated.
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Symptoms of Wild Parsnip Poisoning in Horses
Signs can vary among individual horses, but generally include a skin sensitivity that affects white or light colored skin areas. Symptoms include:
- Skin rash
- Redness on skin
- Skin swelling
- Serum oozing from skin
- Hard skin crusts from dried serum
- Severe pain when touched
- Severe skin photosensitivity that causes a sunburn on white or light colored skin areas after UV light exposure
Causes of Wild Parsnip Poisoning in Horses
The cause of wild parsnip poisoning is the ingestion of any part of the plant, fresh or dried. Though not a usual source of food for horses, they will ingest wild parsnip in certain circumstances. These include:
- Lack of an adequate food source
- Overgrazed pastures and graze lands
- Deprivation of other green vegetation
- Accidental ingestion through hay
The main toxins in wild parsnip are furanocoumarins, which are photoactive. This means that their toxicity is enhanced with exposure to UV radiation. After ingestion, the furanocoumarins circulate in the blood vessels under the skin. White or light colored skin allows the UV radiation, most often from sunlight, to get through, which causes a severe sunburn in those areas. Darker colored skin areas absorb and prevent the UV light from reacting with the toxins. Although the toxic dose of wild parsnip is not known, large amounts seem to be needed to elicit a response.
Diagnosis of Wild Parsnip Poisoning in Horses
If you have seen your horse ingesting wild parsnip, be sure to bring a sample of the plant to your veterinarian’s office so that it can be positively identified. The symptoms your horse is experiencing along with the plant identification can correctly diagnose your horse.
A diagnosis may be more challenging if you have not seen your horse ingest wild parsnip, or any poisonous plant, and your veterinarian will need to eliminate other causes of your horse’s symptoms. Tests for infectious diseases or chemical poisonings can include bloodwork, urinalysis, and serum testing. As these come back negative for other causes, your veterinarian may discuss what is in your horse’s environment. This often leads to evidence of a plant poisoning. A further diagnosis can be made based on the results of gastric contents testing in deceased animals.
Treatment of Wild Parsnip Poisoning in Horses
Treatment for wild parsnip poisoning begins with immediately moving your horse to a shaded area to protect him from UV exposure. Any wild parsnip should be removed from your horse’s pastures and grazing lands, and you should inspect his hay for possible contamination. Your veterinarian may prescribe medications for pain, and antibiotics to prevent any secondary skin infections. Topical treatments can be applied to the affected skin, which could include silver sulfadiazine lotion. Your vet may also recommend bathing your horse to remove crusts and dead skin.
Recovery of Wild Parsnip Poisoning in Horses
Recovery is good for your horse, as long as wild parsnip is removed from the diet. You may be given medications to administer and lotions to apply to encourage your horse’s recovery. Bathing your horse several times a week may also help his skin to return to normal.
Your horse is not naturally attracted to wild parsnip, but will eat it in certain situations. Prevent your horse from ingesting wild parsnip by using weed management plans and monitoring hays and forage. Always wear gloves when handling wild parsnip. Minimize or eliminate this toxic plant from your property through these strategies:
- Learn to recognize wild parsnip, and survey your horse’s pasture and grazing areas for it
- Be sure to eliminate wild parsnip from your horse’s pasture or forage areas before it flowers to prevent seed production; this can be through hand pulling, herbicides, or mowing
- Inspect hay for signs of wild parsnip contamination
- Do not feed hay harvested from ditches to horses
- Always monitor trails for wild parsnip to ensure your horse does not consume it while riding
- Create a plan to manage weeds along fence lines, field edges, ditches and roadsides
- Do not overgraze pastures or grazing areas
- Monitor grazing habits of your horse, particularly after introducing new pastures