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Foxglove is a plant which can be found quite commonly anywhere in the United States and it is one which reseeds itself to maintain its existence. This plant is hardy enough to withstand winters pretty much anywhere in the country and has been used as an ornamental plant around homes and other buildings. The toxins found in foxglove are at their greatest concentrations (and therefore most dangerous to your horse) in the fruit, flowers and immature leaves, and dried leaves can hold their toxicity. It’s not as tasty to your equine as other grazing sources are so the risk of consumption is reduced except when other food sources are scarce or when it is picked and purposely given to the horse for feed (or included in the hay being fed).
Foxglove poisoning refers to the poisoning resulting from the horse’s consumption of the foxglove plant (Digitalis species). The toxins present in foxglove interfere with the electrical conductivity in the heart, causing irregular heart rates and rhythms.
While the signs and symptoms of foxglove poisoning can show up within a few hours, it is also important to know that these symptoms and signs of toxicity can be delayed up to 12 hours from the time of ingestion by your horse. Also, please be aware that the animal may be found dead. Almost all animals are susceptible to the effects of foxglove poisoning. Here are some of the symptoms and signs that might be seen after ingestion:
Profound weakness - horses may not be able to raise their heads
There aren’t really any types per se of foxglove poisoning in horses except as the plant which was consumed by the horse in question. There are other plants which are commonly used as ornamentals around our homes and buildings which contain the same toxin, having the same effect on the horse in question. In addition to foxglove, those plants would be:
All of these plants/trees can be found virtually anywhere in the country, are generally used as decorative shrubbery around homes and buildings and can cause the death of your horse when ingested.
The cause of foxglove poisoning in horses is in the cardenolides (cardiac glycosides) contained in varying degrees of concentration in all parts of the plant. The cardenolides interrupt the function of the sodium-potassium ATpase, allowing an accumulation of intracellular calcium in heart cells. As the intracellular calcium accumulates in the heart cells, the electrical conductivity of the heart is affected, which causes heart rate and rhythm irregularities, which will ultimately lead to the death of the equine.
Because the signs and symptoms of foxglove poisoning can occur within a few hours of ingestion, diagnosis and treatment options are extremely limited at best. Sometimes the animal may be found virtually at the brink of death or already gone, making diagnosis and treatment moot issues except during necropsy. Generally, the diagnosis is made from the history from you and the signs and symptoms being presented by the horse. Lab testing and other diagnostics are usually not available options because the poisoning can progress so rapidly.
As noted above, treatment for foxglove poisoning in horses is generally extremely limited because the toxins can progress to death so quickly after ingestion. Of course, your first action upon recognizing the symptoms would be to remove the horse from the environment in which the poisoning occurred. If your vet gets involved quickly enough, he can sometimes utilize activated charcoal, followed by mineral oil to decontaminate the horse’s digestive system. If the horse is hospitalized, sometimes vets can use medications like atropine and lidocaine to zero in on specific cardiac conduction irregularities. Beyond, these actions, treatment options are limited.
Recovery from foxglove poisoning is slim at the very best. Generally, because the poisoning can progress to death within a few hours of ingestion and because most horses who are grazing in pasture aren’t under 24/7 monitoring, the chances of finding the horse after symptoms have begun and getting appropriate emergent medical treatment, the prognosis for your horse is quite poor. It is to your benefit and to the benefit of your remaining herd, to acquaint yourself with the above-mentioned poisonous plants and be sure to rid them from access to your horses and other animals, whether in pasture or in the hay being fed.
These plants don’t have to be present within the pasture from which your animals graze as the leaves can drop into your field from neighboring tracts or fields or even be present in the hay that is being fed and, since even the dried leaves still contain enough toxin to kill, your animals are still at risk. Take all possible steps for eradication of these plants and be vigilant as they reseed to proliferate from year to year.
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