What is Black Henbane Poisoning?
These plants contain several glycoalkaloids that are highly toxic to horses such as hyoscine (scopolamine), hyoscyamine (L-atropine), and atropine (DL-hyoscyamine). When horses consume these alkaloids, their nervous system is blocked from receiving messages from the parasympathetic receptors. In other words, the brain is not able to get messages to the glands, stomach, heart, and the central nervous system. This increases the heart rate and decreases blood pressure to a dangerous level.
Black henbane can grow up to 36 inches tall and has thousands of hairs that make the plant feel sticky when touched. The leaves are hairy and jagged, with shallow lobes that have a foul smell. The flowers (which bloom in the summer between June and August) are shaped like funnels with five lobes and are yellow-green to brownish yellow. They all have purple centers and veins. The entire plant has the tropane alkaloids scopolamine, atropine, tropane and hyoscyamine, but the seeds are the most toxic. Although horses do not usually find black henbane to be appetizing, almost any horse will eat it if there is nothing else to eat. The fruit is shaped like an urn and releases hundreds of hard brown seeds when ripe.
Black henbane (Hyoscyamus niger), also known as hog’s bean or stinking nightshade, is a toxic plant in the potato (Solanaceae) family.
Symptoms of Black Henbane Poisoning in Horses
The symptoms of black henbane poisoning can vary depending on the amount eaten, size of your horse, and how often it has been consumed. However, the most common signs of toxicity are:
- Dry mouth and throat
- Blurry vision that can lead to blindness without treatment
- Dilated pupils
- Eye pain
- Appetite loss
- Muscle spasms
- Fast and irregular heart rate
- Euphoria and abnormal sexual arousal
- Delirium and hallucinations
- Liver damage (yellow skin and eyes, weakness, lethargy)
- Respiratory paralysis
- Acute black henbane poisoning includes eating a large amount of the plant in a short amount of time
- Chronic black henbane poisoning includes eating a small amount over a long period of time
Causes of Black Henbane Poisoning in Horses
There are several alkaloids in black henbane, which include:
Diagnosis of Black Henbane Poisoning in Horses
Testing for black henbane poisoning includes checking blood counts, chemical profile, tissue (lesions, intestinal tract, kidney, lung, liver) biopsy, stool sample, and urinalysis. If you can bring in a sample of the plant, that would be extremely helpful. If not, take a photograph with your phone to show the veterinarian. This will help with diagnosis and treatment planning. The veterinarian will also need to know your horse’s medical history and whether or not you have given any medications within the last few days.
An electrocardiograph (EKG) will be done first to check your horse’s heart rate because of the cardiac irregularities that henbane can produce. A physical assessment will be performed next, which will likely include temperature, pulse, heart rate, height, and weight. The veterinarian may also want to do a lameness evaluation of your horse. Routine blood tests such as a CBC, biochemistry panel, and blood gases will be performed as well as a battery of radiographs (x-rays) if the veterinarian believes they are necessary.
Treatment of Black Henbane Poisoning in Horses
If your horse has just eaten the henbane recently, the veterinarian may try to decontaminate and flush the toxins from the system.
This step includes giving your horse activated charcoal by mouth to absorb the toxins that have not been digested yet. A gastric lavage may also be done to rinse away any plant residue from the gastrointestinal system. This can also help the veterinarian verify that your horse ingested black henbane by visualization of the plant in the stomach contents.
Intravenous (IV) fluids to flush the kidneys will be done after the decontamination. This is also important to prevent dehydration if your horse has had diarrhea.
A drug called physostigmine, which is a cholinergic medication, may help to reverse the effects of the atropine. Another choice for treating atropine ingestion is neostigmine or prostigmin.
Supportive treatment includes oxygen therapy, ice packs or a hypothermia blanket to reduce fever, and continuous fluids and electrolytes to prevent further dehydration.
Recovery of Black Henbane Poisoning in Horses
Continue to monitor your horse for the next several days to be sure there are no further complications and call your veterinarian if you have any questions or worries. You should walk around your fields and pastures to look for black henbane or other poisonous plants. If you find anything suspicious you can pull the plants or dig them up. Be sure to get the entire root and treat with herbicides to be sure.