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Cocklebur plants can be found all around the world, and are most common in North America and Eurasia. Belonging to the Asteraceae family, cockleburs are an annual weed that can grow to 3 to 5 feet tall, with dark brown, purple, or red spotted stems and branches. Leaves are triangular in shape, and the male and female plants produce different green to white flowers, either terminal branches of flowers or flower clusters near the leaf axils. They are found in moist soils of reservoirs or floodplains, and in cornfield, pastures, or fencerows.
Cocklebur poisoning occurs when a horse ingests the cocklebur plant. Though generally unpalatable, there are conditions when a horse would eat this toxic plant, of which the seeds and seedlings are the most deadly parts. You may have seen the spiny seed burs tangled in your horse’s mane or tail after grazing. Signs of depression, weakness, and muscle spasms can appear rapidly after ingestion, and can progress just as quickly to convulsions, coma, and death.
Signs of cocklebur poisoning in your horse generally appear within hours after ingestion. Symptoms can worsen as the liver damage progresses, leading to death within 1 to 2 days. If your horse survives an acute poisoning, he will generally show symptoms of chronic liver disease. Symptoms include:
The cause of cocklebur poisoning is the ingestion of the cocklebur plant, which contains the sulfated glycoside carboxyatractyloside. This toxin interferes with a cell’s ability to make energy, and directly affects the liver.
Carboxyatractyloside is present in all parts of the cocklebur plant, but is at its most potent in the seeds and seedlings, usually prominent in the spring and summer seasons. The plant is also at its most palatable as a seedling, making it a dangerous combination for a hungry horse. Ingestion of only 0.75% of a horse’s body weight can result in a poisoning.
Cocklebur itself is not a primary food source for horses, and they will often avoid it due to a bitter taste and rough texture of a mature plant. The seeds are enclosed in spiny capsules and are usually avoided. But there are times when a horse may eat a cocklebur. These include:
Diagnosis is most commonly made on the identification and evidence of cocklebur consumption and symptoms presented. If you aren’t sure what kind of plant your horse has eaten, bring a sample to the equine veterinary clinic to identify. Testing has not been shown to be reliable, and at this time there isn’t a definitive way to test if your horse has been poisoned by cocklebur. Stomach contents can be examined, but this often only occurs post mortem. However, due to the severity and quick progression of the symptoms, your veterinarian should begin treatment immediately in the presence of any signs of poisoning.
At this time, there is no treatment available to counteract the disruption of cellular function caused by the toxin carboxyatractyloside. Therefore, treatment is aimed at reducing the absorption of carboxyatractyloside and using supportive therapies. Due to the rapid nature of cocklebur poisoning, treatment may be too late once symptoms are seen.
Activated charcoal or mineral oil can reduce the absorption of the toxin. Fatty substances can also be used, such as vegetable oil, lard, and whole milk or cream. Low blood sugar can be helped with an intravenous glucose injection. Muscle relaxants can be prescribed to reduce muscle spasms.
Removing the source of contamination is paramount. Check pastures and hay for evidence of cocklebur, and eliminate it wherever possible through mowing or use of herbicides. Be sure to feed your recovering horse clean food and water.
As with any poisoning, quick action is needed for any kind of recovery. Due to the highly toxic nature of cocklebur, once symptoms appear, it is often too late for your horse to recover. Seeking medical attention immediately is the best chance for your horse to survive, but the prognosis is still poor. Prevent your horse from ingesting toxic cocklebur by using these strategies:
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