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What is Switchgrass Poisoning?

Switchgrass, scientifically named Panicum virgatum, is a common addition to the diet of cattle, but it contains several different sapogenins that are photo and hepatotoxic for horses, sheep, and goats. When eaten in large quantities it can lead to liver damage, and exposure to the sun after consuming switchgrass may lead to a rash that may have open lesions. There are several types of hay that are safer for equines, such as alfalfa and oat hay.

Switchgrass, although a good addition to the hay and pastures of cattle, can be detrimental to the health of other animals, including horses, sheep, and goats.

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Symptoms of Switchgrass Poisoning in Horses

Symptoms of Switchgrass poisoning include symptoms of both photosensitivity and liver disease. 

Liver Dysfunction

  • Depression
  • Incoordination
  • Jaundice
  • Lameness
  • Loss of appetite
  • Weight loss

Signs of photosensitization can occur on any part of the body but are most often found in places where the hair is sparse or in areas of low pigment. These signs can include: 

  • Bumps on skin
  • Mouth ulcers
  • Oozing sores 
  • Peeling or reddened skin

Types

There are several types of hay available to feed your equine that are much safer than switchgrass. These can include:

  • Alfalfa - Alfalfa is a legume hay, with a higher protein content and calcium levels, but it may trigger bouts of laminitis if fed to insulin resistant equines
  • Coastal Bermudagrass - This is a high-fiber grass hay that is most commonly seen in the southern states; hay made from low-quality Bermudagrass can cause impactions in horses 
  • Oat - A type of grass with particularly tough stalks, oat grass is hardy and takes longer to eat, but it can be too high in sugar for insulin resistant animals
  • Timothy - Timothy hay is higher in calcium than other grass hays and contains ample quantities of vitamins A and Ds, but is generally more expensive than other hays

Causes of Switchgrass Poisoning in Horses

The toxic element contained in the switchgrass is a naturally occurring steroid known as a sapogenin. This compound is the instigator of both the digestive upset that the patient experiences and the dermal reaction from the sap. Skin reactions to the sap generally start out mild and short-lived, but they do intensify and last longer with repeated exposures.

Diagnosis of Switchgrass Poisoning in Horses

The proper identification of the plant in the pasture may be sufficient to make an initial diagnosis. If you can obtain a sample of the plant, this will assist in the correct identification as there are several kinds of grass with a similar appearance. Your veterinarian will need to note information regarding estimates of the amount of plant material that was ingested and how long it has been since it was eaten. They will also gather a comprehensive history of the animal in question including as much knowledge as possible about the horse’s medications, diet, and environmental elements. 

Standard blood tests, including a complete blood count and  biochemistry profile, will need to be evaluated to see if any infections are present as well as establishing the levels of liver and kidney enzymes found in the blood. A sample of any skin that has been affected by phototoxicity will be evaluated by cutaneous cytology. This microscopic examination will help reveal if mites, fungal infections, or allergies might be causing the rash. Phototoxicity is generally more conspicuous on areas that have low pigment or that are the most exposed to the sun.

Treatment of Switchgrass Poisoning in Horses

If the consumption of large quantities of switchgrass was recent, then your horse’s doctor will most likely perform a gastric lavage in order to remove as much of the sapogenins from the digestive system as possible. The administration of activated charcoal is also a standard treatment, utilized to prevent further absorption of the toxic compound into the bloodstream. There is no effective antidote for sapogenins, making most treatments beyond decontamination supportive in nature. 

Examples of supportive treatments that may be utilized include IV fluids to prevent dehydration and combinations of electrolytes and sugars in order to adjust for any imbalances that may have developed. Animals that show signs of photosensitivity should be immediately moved out of the sunlight. Avoiding sunlight for 48 hours after the exposure will significantly reduce the likelihood that disfiguring skin damage will develop. In those cases where skin damage does occur, medications such as corticosteroids, anti-inflammatories, and antihistamines may be prescribed to ease the patient’s discomfort. Medications like this may be administered either orally, topically, or by injection.

Recovery of Switchgrass Poisoning in Horses

It is important to evaluate the hay that your horse eats and the pastures that they graze in on a regular basis. Switchgrass is an excellent crop for bioenergy fuel, and although it is toxic to horses, sheep, and goats, cattle have no difficulty in processing this abundant plant. Switchgrass is often used as hay for cattle as they find it nutritious and palatable. The drying process does not destroy the saponins that are located in the plant, and if your horse eats dried hay comprised of switchgrass, then symptoms of toxicity may emerge. Because of its palatability it is often used in cattle grazing pastures, but it should be avoided in fields where horses, sheep, or goats visit.