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The Texas Umbrella Tree, known scientifically as Melia azedarach, is a member of the mahogany family that sprouts delicate light purple flowers in the spring, which develop into yellow, berry-like fruits in the summer. These deciduous trees are native to Australia, China, and India, and they were introduced to North America in the early 1800’s. They have since escaped into the environment and thrived, categorizing them as an invasive species in several southern states.
Known more commonly as the Chinaberry tree, they produce a very effective insecticide which utilizes a tetranortriterpene neurotoxin known as meliatoxin. This poison is found throughout the plant’s bark, leaves, and flowers but the ripened fruits contain the highest concentrations. If you suspect that your horse has consumed any of this plant, contact your veterinarian immediately.
The Texas Umbrella Tree, or Melia azedarach, is a deciduous tree that produces a potent neurotoxin which it utilizes as an insecticide. This chemical, known as meliatoxin, can be fatal in relatively small doses.
Symptoms of poisoning from sampling the Texas Umbrella Tree usually begin within a very short time, typically just two to four hours from ingestion. Although poisonings most often are triggered by eating the ripe fruit, the bark, leaves, and flowers also contain reduced amounts of the toxic compounds.
The scientific name for the Texas Umbrella Tree is Melia azedarach, and it belongs in the mahogany family. It is most commonly known as the Chinaberry tree, but it has several other names as well, including:
Also in the mahogany tree family is Azadirachta indica, or the neem tree, which produces an insecticide called azadirachtin, which is very similar to meliatoxin, but much less potent. The neem tree is similar in appearance to the Texas Umbrella Tree, but the oil it produces can be diluted and used to protect horses from insects. In some cases, the azadirachtin in the oil may cause contact irritation to the skin, and ingesting large quantities may lead to gastrointestinal discomfort.
The toxin in the Texas Umbrella Tree is a tetranortriterpene neurotoxin known as meliatoxin, which is most concentrated in the small ripe fruits that are produced in the summer. Meliatoxin developed as a natural insecticide to prevent insect infestations. Although this neurotoxin is also present in the flowers, leaves, and bark of this plant, it is not typically in high enough concentrations to cause the severe toxicity seen when the fruits are eaten. This tree was introduced to the United States sometime in the early 1800’s and has become an invasive species in many areas of the southern United States since then. The seeds of the Chinaberry tree are rapidly spread by birds who are immune to the toxin in the fruit.
If you believe your horse has sampled the Texas Umbrella Tree, do not hesitate to contact your veterinarian, especially if it is possible that the fruits or seeds were consumed. The concentrated meliatoxin that is located in the fruit of the chinaberry tree is frequently fatal within twenty-four hours without supportive care, and seeking that treatment early is the best course of action for a positive outcome. A comprehensive history of the horse in question may be requested, including information about the individual horse’s symptoms, medications, daily diet, as well as the amount of plant material that was likely to have been ingested and how long it has been since that consumption took place. This information, combined with the identification of the tree near the pasture or stables will help to formulate an initial diagnosis.
Your veterinarian will also assess the results from the standard blood tests, including a biochemistry profile and a complete blood count to see if any infections or any blood sugar imbalances are present as well as establishing the liver and kidney enzyme quantities found in the patient’s blood. Fecal matter is also typically floated to check for parasites, and the presence of plant material in the manure may help to confirm the initial diagnosis.
If material from the Texas Umbrella Tree was consumed within the last few hours, your horse’s doctor would typically perform a gastric lavage procedure as soon as possible in an attempt to remove as much of the toxic material from the horse’s stomach as possible, and the contents will be further evaluated by the examiner. Once the majority of the physical plant material has been removed from the stomach, activated charcoal is generally administered in order to prevent further absorption of the tetranortriterpene neurotoxin into the bloodstream.
There are no known antidotes for the potent neurotoxins that are produced by the Texas Umbrella Tree, so once the decontamination procedures have been completed, the remaining treatments will be focused on supportive therapies. Supportive treatments for poisoning typically include intravenous fluid therapy to counteract dehydration as well as electrolytes and sugars to correct imbalances that may occur. Oxygen will be made available if breathing becomes labored, and pain management medications may be recommended to ease discomfort and reduce any swelling.
The prognosis for horses that ingest enough of the toxin to develop symptoms is guarded to poor as fatalities can occur from the consumption of just half a percent of the animal’s overall body weight. If you suspect poisoning from eating the fruit and seeds of this tree, it is best to seek medical treatment as soon as possible as animals that are exposed to sufficient amounts of this toxin will generally either recover or succumb within around twenty-four hours. Although seeking supportive care early does not guarantee that your horse will overcome this poison, it will greatly improve their chances.
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