What is Poison Hemlock Poisoning ?
Poison hemlock (scientific name Conium maculatum) is a biennial that can be up to seven feet in height with hollow stems that divide at their top, in many cases dappled with purple spots. Poison hemlock tends to have a scent similar to parsnips or parsley when the leaves of the plant are crushed. White flowers are clustered in umbrella shapes in the plant. In its first year of growth, poison hemlock will display leaves with a lacy appearance near the ground. In its second year, a straight stalk that flowers will develop.
The plant is found throughout most of the United States, though not in northern Minnesota, the Dakotas, eastern Montana and Wyoming. Poison hemlock is found in swamps and lowlands, typically in water or right at the edge of it. How toxic the plant is will depend on the following:
- Where it is in its growth process
- Conditions of the environment (rain, temperature and cloud cover)
All of the parts of the plant are toxic, though the most toxic are the fruit that is still green, fruit that is ripe, and the stems.
While horses don’t necessarily find these plants tasty, they can ingest them by mistake or if food is scarce. Poison hemlock can also be present in contaminated hay.
Found throughout much of the United States in swamps and lowlands, poison hemlock is very toxic to horses when ingested and can lead to death.
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Symptoms of Poison Hemlock Poisoning in Horses
Should your horse ingest poison hemlock, you may see the following symptoms within an hour ingestion:
- Muscle tremors
- Muscle weakness
- Lack of coordination
- Frequent urination and defecation
- Loose stools
- Dilated pupils
- Appearing disoriented
Symptoms will progress and your horse may then experience the following:
- Significant depression
- Only lying down
Poison hemlock is found to be fatal when the horse ingests 0.2 to 0.8% of his body weight, which would be between two and eight pounds for a horse weighing 1000 pounds.
Poison hemlock has eight piperidine alkaloids, though two of them are usually the most abundant and the main cause of both acute and chronic toxicity. These are coniine (which is derived from pyridine and has a function similar to nicotine) and y-coniceine.
Causes of Poison Hemlock Poisoning in Horses
Poison hemlock’s alkaloid concentration will typically increase as the plant becomes more mature and is at its peak in seeds. As the plant dries the concentration decreases though it can still be toxic when in hay. The alkaloids contained include: coniine, N-methylconiine and gamma-coniceine.
The poison hemlock plant is very toxic in horses. While all parts of the plant include the poisonous alkaloids, the fruits have the largest concentration. The plant will give off a foul odor when it is crushed and horses will rarely eat it because of its taste. When the poison hemlock plant is harvested with hay it will maintain the toxic properties.
Diagnosis of Poison Hemlock Poisoning in Horses
In cases of poisoning by poison hemlock, death can occur within hours, therefore a quick diagnosis is important for the survival of your horse. Should you notice your horse ingest poison hemlock, see that something is amiss with your horse, or witness any of the symptoms above, you will want to contact your veterinarian immediately. A quick diagnosis is imperative to ensure a good outcome for your horse; therefore, it is a good idea to look around the area where your horse has been in order to see if there are any poisonous plants that he may have ingested. You can bring samples of the plants to your veterinarian, as this may assist him as he seeks to diagnose your horse. While the stomach contents and feces of your horse can be tested, in the case of poison hemlock poisoning, there may not be the time to wait for the results.
Treatment of Poison Hemlock Poisoning in Horses
There is no antidote for poison hemlock poisoning. Should your horse experience poison hemlock toxicity, your veterinarian will focus on clearing out his stomach contents. In some cases, respiratory support will be necessary, as respiratory failure can occur as a result of the poisoning. If the stomach of your horse is cleared of the poison and your horse receives the support he requires until the last of the poison leaves his digestive tract, he can recover.
Recovery of Poison Hemlock Poisoning in Horses
Should your horse experience poison hemlock poisoning, it is important to follow the instructions of your veterinarian and attend follow up appointments as necessary.
Horses that survive for eight hours after symptoms have begun are more likely to recover, with the exception of those who have complications from seizures. Supportive care will likely be required as your horse recovers from the poisoning.