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What is Milkvetch Poisoning?

Milkvetch, or astragalus, belongs to the family Fabaceae, which is a legume. The genus is the largest genus of any plant, and originates from temperate areas of the northern part of the world. This plant is found in North and South America, Europe, Asia, Northern Australia, and Northern Africa. There are over 400 species in North America and much of the plant does reach most of North America. 

The Astragalus plants come in many different varieties, and many (24 species of milkvetch) contain selenium and grow in selenium-rich soils. Two-grooved milkvetch is one species that contains high amounts of selenium and is toxic to horses and livestock. The toxic principles of the selenium in milkvetch give the plant a characteristic odor of garlic, especially when in warm weather. The plant itself has a pattern which branches up into an ascending pattern with green or red-tinted stems. Flowers on the plant are purplish in hue with a hint of pink color as well. The pods are slender and grooved, and in two-toned species the midveins contain two grooves.

Selenium is a necessary trace mineral. It is a powerful antioxidant and is good for the horse’s immune system. It is an ingredient in many horse feeds. However, when consumed in high quantities (as with many vitamins and minerals) it can be damaging to the horse’s health. Horse owners should test the soil of their property for selenium content and check for selenium-containing plants.

Milkvetch poisoning in horses is a result of horses ingesting selenium-containing milkvetch, which makes up over 24 species of this toxic plant.

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Symptoms of Milkvetch Poisoning in Horses

If your horse consumed this type of Milkvetch, he will be exposed to selenium. Although necessary for a horse’s diet and nutrition, high amounts are toxic to horses. Symptoms include:

  • Weakness
  • Clumsiness
  • Hoof problems
  • Loss of appetite
  • Blindness
  • Lameness
  • Lethargy
  • Confusion

Types

Milkvetch has several different types of names which are very important to know, especially if you own horses. Other types of names for milkvetch include:

  • Astragalus
  • Goat’s Thorn
  • Two-grooved Milkvetch
  • Stinking Milkvetch
  • Patterson Milkvetch
  • Alkali Milkvetch
  • A. Gummifer
  • A. Tragacanthus

Causes of Milkvetch Poisoning in Horses

Milkvetch poisoning in horses can occur from the time of consumption of the plant. Specific causes of milkvetch poisoning in horses include:

  • Depletion of enzyme activity due to selenium amounts in the plant
  • Vitamin E protects the destruction of cellular membranes by free radicals.
  • Cellular functions are disrupted
  • Tissues become damaged through oxidation

Diagnosis of Milkvetch Poisoning in Horses

If you suspect your horse has Milkvetch poisoning, contact your veterinarian immediately. If you have a sample of the Milkvetch, it will be helpful to bring it with you to show the veterinarian. Your veterinarian will conduct a complete physical examination, which may entail blood work, urinalysis, and biochemistry profile. He will also want more information about any toxic plants where your horse grazes or has contact with. 

Your veterinarian may perform several tests to be sent to a laboratory. He may choose to test your horse’s feed to check for any traces of toxic plant matter, your horse’s blood serum content, and perform a tissue test to check for selenium amounts. He may also take a closer look at the hooves of your horse for characteristics of selenium toxicity. If your horse’s hoof contains 5-20 ppm selenium content, this is considered a toxic amount.

Your veterinarian may want to test your horse’s stomach contents, along with his fecal matter to check for plant particles. Your medical professional will more than likely begin treating your horse’s symptoms right away; your veterinarian is knowledgeable in detecting poisonous plant toxicity by looking closely at the clinical signs your horse is showing. Fluid therapy may be started and symptomatic treatment may begin while he is awaiting any lab results.

Treatment of Milkvetch Poisoning in Horses

Unfortunately, there is no antidote or remedy for selenium toxicity. Your veterinarian will only treat his symptoms to the best of his ability. He will give him fluids to help flush out his system and closely monitor your horse. 

There are ways to give your horse the treatment he needs for this toxicity over time. Even though there is no immediate “cure” for this poisoning, your medical professional will give you suggestions on things you can do to help your horse recover at home.

Your veterinarian will recommend that your horse is completely kept away from any feed which has any amount of selenium at this time. He will suggest that you feed him a high-protein diet, plenty of fresh water, and continue to watch over him closely for any new symptoms or behaviors, such as unexpected lameness.

Recovery of Milkvetch Poisoning in Horses

It is very important that you remove any Milkvetch from your property. Milkvetch can be removed by you or with the help of a knowledgeable professional who knows each type of toxic plants. If your pasture contains a high amount of Milkvetch and soil that is high in selenium amounts, you may need to relocate your horse to another area for at least temporarily.

Your veterinarian will want to revisit your horse to be sure he is recovering properly. He may perform tests once again and compare the selenium amounts in his system to the prior amounts.