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The twining woody vines of the Celastrus scandens plant, better known as American bittersweet, contain sesquiterpene lactones and euonymin, which can cause toxicity if ingested by horses in large amounts. This plant is native to the central and eastern areas of North America and was historically used as a human purgative by American Indians and pioneers, and the berries are favored by birds. The toxic compounds that affect horses and humans are found throughout the plant, but they are most concentrated in the unripe berries.
American bittersweet (Celastrus scandens) contains chemical compounds such as sesquiterpene lactones and euonymin, which are irritating to the animals to the nose, eyes, and gastrointestinal tract.
American bittersweet is not often palatable to horses, but if it is consumed, it can be toxic, particularly if the unripened green berries are eaten. Some of the signs and symptoms that may be present with this type of toxin can include:
American bittersweet (Celastrus scandens)
A twining, woody vine that can reach up to thirty feet in length and can reach an inch thick at their base. The vine sprouts tiny, unfragranced flowers that transform into pea-sized orange fruits. Although birds thrive on these fruits, they are toxic to horses, particularly when unripe.
Oriental bittersweet (Celastrus orbiculatus)
Oriental bittersweet is very similar in appearance to American bittersweet, however, the vines are thin and spindly compared to the American variety and have a reddish brown bark. The small green flowers develop into yellow fruits which split open to reveal large red seeds. Oriental bittersweet is considered an invasive species in the United States.
Both the American bittersweet plant (Celastrus scandens) and the Oriental bittersweet plant (Celastrus orbiculatus) are believed to contain sesquiterpene lactones, which are severely irritating to the nose, eyes, and gastrointestinal tract. They are also one of the few plants to contain euonymin, a chemical found more commonly in the spindle tree. Although all parts of the plant contain the toxic compounds, the unripe berries contain the highest concentrations.
Your veterinarian will typically start the visit by taking biological samples to evaluate using standard tests like a biochemistry profile, urinalysis, and complete blood count, to check for toxins that are detectable in the blood or infections, however, euonymin and sesquiterpene lactones are not typically revealed from these tests. Your veterinarian will also perform a full physical examination and will typically take note take note of any plants that are growing in the fields or stabling area as well as information regarding any other supplements or prescriptions that have been administered to your horse.
This information helps to uncover any toxins or drug interactions that are known to induce the same symptoms as bittersweet poisoning. A sample of the horse’s feces will be evaluated as well, and any plant material that is found in the feces may assist the examiner in establishing an accurate diagnosis. Neurological tests are often completed at this time as well to determine the extent of the temporary neurological deficiencies.
No specific antidotes are available for the euonymin, or the sesquiterpene lactones that are produced within the bittersweet plants, so supportive therapies are the emphasized primary treatments. Dehydrated horses will receive intravenous fluid therapy as soon as possible. This hydration therapy will also provide needed balance to the levels of electrolytes and sugars that are currently present in the blood. Horses that have been intoxicated by American Bittersweet may fail to adequately care for themselves and are at an increased risk of injury, and this is also the time that any injuries that may have occurred due to lack of coordination will be addressed.
Once these immediate supportive requirements have been satisfied, then the next course of action will focus on the normalization of the horse’s daily diet. The affected horse should avoid grazing in any pastures that contain either type of bittersweet or other plants that contain sesquiterpene lactones or euonymins, such as sage plants, mugwort, spindle tree, or burdock, and should be placed on a balanced diet as soon as possible.
The prognosis for poisoning by either type of bittersweet plant is quite good, and most horses recover completely within one to two weeks. The toxic reaction from eating too much bittersweet is easily reversible in most cases, however, the loss of coordination and the mental obstruction can lead to dangerous levels of disorientation as well as injuries. As with most poisonings, damage to the liver and kidneys are possible, particularly if the amount ingested was very large or if treatment is delayed. Your veterinarian may want to repeat blood tests after the horse has recovered to ensure the continued functionality of these organs.
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