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Gum weed is also known as resin weed, curlycup gum weed, and its biological name of grindelia squarrosa and can be found in the dry, alkaline soils generally located in the western states. As such, it is a plant that is found in pastures and other forage areas in which horses and other livestock can be found grazing. It is typically not a plant which horses find tasty, so consumption of it is usually not a problem except when other preferred forage is scarce. When it is consumed by your horse, problems with too much selenium in their systems begin to surface, sometimes leading to permanent damage or death.
Gum weed (Grindelia Squarrosa) is poisonous to horses as it is considered a “selenium accumulator”, affecting the normal make up of keratin which is the primary component in the structure of the horse’s hooves and hair.
As noted above, the gum weed plant isn’t very tasty to your equine, but if other feed is scarce, he will ingest it. Here are some of the symptoms you might notice if this occurs:
Some of these symptoms will present earlier than others and the severity and chronology of presentation will be determined by the amount of gum weed (which is dependent upon the length of time he was exposed to the weed) which has been ingested. For some animals, less of it will be problematic while others may tolerate higher quantities without major complications for awhile.
Gum weed poisoning in horses occurs as a result of the plant being a “selenium accumulator”, meaning that it causes changes in the selenium balance in the horse’s system. This causes selenium toxicosis due to elevated levels of selenium in the horse’s system. There are two types of selenium toxicosis:
Acute - Cases in which sufficient amounts of the plant have been ingested to cause severe symptoms (weakness, abnormal movements, bloating, abdominal pain, fever to name a few symptoms), death generally occurs within hours at this level of substance ingestion
Being a “selenium accumulator”, ingestion of this plant can, in various amounts, cause problems with the selenium balance required for good health of your horse. The selenium contained in the plant accumulates, causing imbalances which lead to selenium toxicosis which leads to the types and conditions explained above. Some of the other effects of the alkali disease/selenium toxicosis/gum weed poisoning can sometimes be found in the liver and in the heart as well. This end result is, of course, dependent upon the amount of gum weed ingested by the equine and the length of time the horse is exposed to it. Also as noted above, this plant is not a forage of choice by your horse but rather something that he will eat if he has little other forage available.
The diagnosis of gum weed poisoning will consist of a thorough physical examination by your veterinary professional in which he will be noting the condition of the hair and hooves of your equine, the energy levels, abdominal girth and pain responses elicited with palpation and examination and the general overall appearance of your horse.
Since gum weed poisoning involves a “selenium accumulator”, the veterinarian will likely require some blood work and, perhaps, even some tissue samples to be evaluated in the laboratory as the blood chemistries and tissues of animals suffering from selenium poisoning will be affected. He will likely also need samples of feeds, grains, forages and water which have been considered part of the diet of the afflicted equine so appropriate laboratory testing can be done on it. In all of the samples taken and tested, they will be looking for elevated levels of selenium content needed to make the correct diagnosis.
At this time, we have no specific treatment for selenium poisoning (gum weed poisoning). The first step likely to be recommended by your vet will be to remove the afflicted animal from exposure to the gum weed plant as soon as possible. After that, supportive treatments and treatments germane to the symptoms being displayed by the equine will likely be initiated.
Your vet may also initiate the use of substances to be included in the horse’s diet which are intended to inhibit the effects of the selenium excess as this may help to reduce the risk of progression of selenium toxicosis to more severe stages. And, this step in the treatment plan may actually be extended to other horses in your herd who may be suffering of the same affliction in earlier stages if they are being exposed to the same feed, grain, forage and/or water as the horse who is being treated.
Reported cases of gum weed poisoning, or selenium toxicosis, reveals that those equines who suffer from chronic poisoning will not likely flourish even after you have removed them from exposure and have provided the best treatment for the condition, while others of their herd-mates who have not been chronically poisoned by ingestion of gum weed will likely fare better. Depending on the duration of the exposure and the severity of the poisoning, it would be prudent on your part to expect that your horse, in cases of severe toxicosis, will, at best, be compromised for the rest of his life or, at worse, will not survive.
It is imperative, for this reason, that you regularly check any pastures, forages and feeds which if you are located in high-selenium areas for unsafe levels of this substance. This is recommended to be done at least annually so that you can plan accordingly from year to year for the safety and continued good health of your herd.
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