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What is Queen Anne's Lace Poisoning?

Queen Anne’s Lace (Daucus Carota) is a deciduous perennial that gets its name from a story told about a Queen Anne’s lace-making episode which took place in centuries past.  The plant, considered an ornamental, is also known by some other names: wild carrot, greater ammi, large bullwort, goutweed, Bishop’s weed, carotte sauvage, bird’s nest and carrotte.  The story behind the name is romantic and interesting to be sure and telling the story, stressing the single red or purple flower in the very center of the bloom, can help children tell the difference between Queen Anne’s Lace and the more dangerous Poison Hemlock, which is extremely poisonous to both man and beast.  Queen Anne’s Lace or wild carrots (the better known of its aliases), is also toxic to horses but only mildly so.

Queen Anne’s Lace poisoning in horses is a mild toxicosis that results from ingestion of the ornamental plant which looks quite similar to poison hemlock.

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Symptoms of Queen Anne's Lace Poisoning in Horses

As noted above, while Queen Anne’s Lace resembles poison hemlock, it does not share the extreme toxicity of which poison hemlock can boast.  It is considered mildly toxic to horses and some other animals and here are some of the symptoms you will likely see:

  • Photosensitization - sunburn
  • Difficulty swallowing
  • Blistering mouth
  • Increased salivation
  • Irritation of the digestive tract

Types  

A member of the carrot or parsley family (Umbelliferae), the wild carrot or Queen Anne’s Lace plant has no “types” per se except as the symptoms apply to:

  • Dermatitis or inflammation of the outer layers of the skin causing photosensitization or sunburn
  • Irritation to the oral tissues causing blisters in the mouth, edema to make swallowing difficult and increased salivation
  • Irritation to the digestive tract 
  • Nitrate poisoning based upon the nitrate content in the soil in which it is growing causes the creation of hemoglobin which doesn’t have the ability to carry oxygen, causing oxygen starvation

Causes of Queen Anne's Lace Poisoning in Horses

  • The toxicity of Queen Anne’s Lace or wild carrots lies in the neurotoxins contained in it as well as the nitrates which have been absorbed from the soil in which it grows
  • The neurotoxins cause dermatitis,inflammation and irritation of the outer layers of the skin which cause sunburn, inflammation of the upper layers of the oral tissues in the mouth and throat causing difficulty swallowing, mouth blisters and excessive salivation
  • The nitrates picked up from the soil become nitrates in the digestive system and cause metabolic changes which create hemoglobin which is incapable of carrying oxygen, resulting in oxygen starvation or suffocation

Diagnosis of Queen Anne's Lace Poisoning in Horses

Since this plant is quite prolific and can be found literally everywhere, it is likely that you will have noticed it in your fields and pastures or maybe even mixed into the hay and grain which you feed your horses.  This information needs to be included in the complete history that your vet will require from you as part of the information gathering stage of his assessment of your horse.  He will need to do a physical examination to assess the condition of the afflicted horse and will likely need to order some blood testing and perhaps some testing of various tissue samples.  

Based upon his examination findings, he may wish to utilize radiographic imaging (x-rays) or CT imaging to rule out the many other possible causes of the sickening of your horse as many of the symptoms of Queen Anne’s Lace poisoning can be similar to many other diseases and conditions known to horses.

Treatment of Queen Anne's Lace Poisoning in Horses

The first line of treatment will likely be recommendations from your veterinary professional which involve removal of the afflicted horse from the source of the poisoning.  As a rule, horses will not necessary consume a great deal of wild carrots unless more nutritious forage is not available (due to seasonal changes) or unless the pasture or field has been overgrazed.  But, even in those cases in which there is sufficient lush green forage for your horse, keep in mind that he will munch away without giving thought to what other plants might be growing alongside the more nutritious options in that field or pasture or which may be mixed into the hay and grain that you’re feeding him.  He may be eating it without your knowledge of its presence.  

Beyond removal of the source of poisoning, treatment options for this mild toxicity will be to provide plenty of clean, fresh water and nutritious feed which has been checked for the presence of the wild carrot or Queen Anne’s Lace plant parts.  Supportive care which could include fluids (IV or orally), possibly treatment of any diarrhea with an appropriate medication to stem any continuing fluid loss and close observation while the horse is rested and kept quiet to heal will likely round out the treatment plan developed and recommended by your veterinary professional.

Recovery of Queen Anne's Lace Poisoning in Horses

You should expect that your afflicted horse will likely need some time to heal, making it necessary to keep him in the paddock where rest, clean and fresh water and nutritious food can be provided while he recuperates.  This could take several weeks and, during that time, you will need to closely monitor the afflicted horse, getting your veterinary professional back into the picture quickly if the horse does not appear to be responding appropriately to the treatment. Extra care should be taken to assure that wild carrots or Queen Anne’s Lace plants are removed from areas where you graze your herd and that the hay and grain being fed is also as free as possible from the contamination of any and all parts of this toxic plant.  This will ensure that the remainder of your herd will remain healthy and productive.