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What is Silverleaf Nightshade Poisoning?

Solanum elaeagnifolium, more commonly known as silverleaf nightshade, is a weed that is found throughout North America. The leaves and stems are covered with tiny hairs that give it a silvery appearance, but the stems also have nettle-like prickles. All parts of this plant contain hazardous glycoalkaloids, most notably a glycoalkaloid known as Solanine that can cause gastrointestinal and central nervous system disruptions for horses. Silverleaf nightshade is not palatable to most horses, however, they will consume it when it is located in an overgrazed field.

Silverleaf Nightshade is a common weed throughout North America which contains the glycoalkaloid solanine, a toxin that can cause disturbances in the gastrointestinal and central nervous systems.

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Symptoms of Silverleaf Nightshade Poisoning in Horses

Gastrointestinal symptoms typically present first, then, as the toxin is transported into the bloodstream, the signs of the involvement of the central nervous system become more clearly apparent. 

  • Colic symptoms
  • Coma
  • Depression
  • Diarrhea 
  • Difficulty swallowing 
  • Dilated pupils
  • Excessive drooling 
  • Falling
  • Loss of appetite
  • Loss of coordination
  • Nervousness
  • Paralysis
  • Rapid breathing
  • Seizures
  • Tremors
  • Weak pulse
  • Weakness

Types 

There are several plants in the Solanaceae family of plants that are known as Nightshade in the United States. All of these can be toxic to varying degrees:

  • American black nightshade (Solanum americanum) - This nightshade has small white or light purple flowers that become clusters of round, black berries 
  • Carolina nightshade, horsenettle (Solanum carolinense) - The flowers on this nightshade are generally white or light purple, and the berries are very similar in appearance to small tomatoes; the leaves of this plant also smell of potato when they are crushed
  • European black nightshade (Solanum nigrum) - This plant has white to light greenish flowers and clusters of round, black berries; it is often confused with another plant known as a nightshade, Atropa belladonna, but Atropa belladonna has berries that hang individually rather than in clusters
  • Hairy nightshade, green nightshade (Solanum physalifolium) - True to its name, the hairy nightshade is covered in tiny hairs, although they do not extend to the white or pale blue flowers or the yellowish berries it produces

Causes of Silverleaf Nightshade Poisoning in Horses

The danger in this plant lies in the glycoalkaloid known as solanine that is present in all parts of the plant, although it is most concentrated in the unripe berries. This compound is used by the plant as a natural defense against predators like grazing animals and can be found in differing concentrations in most of the plants in the Solanaceae family, including tomatoes, potatoes, and eggplant. Solanine disrupts the way that the cell membranes function and is known to cause cell death. Silverleaf nightshade is generally unpalatable to horses, but it can become a problem in fields that are overgrazed or if it gets mixed into feed hay.

Diagnosis of Silverleaf Nightshade Poisoning in Horses

If you discover your horse grazing any part of the Silverleaf nightshade, or if you locate the plant growing in the pasture or around the stables, then the symptoms combined with the positive identification of the plant may be sufficient to make a preliminary diagnosis of solanine poisoning. The equine veterinarian will collect as much information as possible about the amount of plant material consumed and approximately how long ago you estimate that this occurred, as these factors will help determine which treatment plant is the most appropriate for your horse.

Standard blood tests will assist in ruling out several other infections or toxins, and more specialized tests may be able to confirm the presence of solanine and possibly even provide data about the amount of the glycoalkaloid circulating in the patient’s bloodstream. Drugs such as beta-blockers, steroids, and even some chemotherapy agents may negatively interact with the glycoalkaloid solanine manufactured by the plant, so information about any prescriptions or supplements that are being dispensed is also significant. An electrocardiogram may be used to check the health of the heart if an elevated heart rate is detected.

Treatment of Silverleaf Nightshade Poisoning in Horses

If your horse is showing symptoms of intoxication by the glycoalkaloid solanine, your horse’s doctor will most likely start treatment with gastric irrigation as quickly as possible in order to remove as much of the Nightshade from the digestive system as possible. Activated charcoal will typically be administered in an attempt to soak up as much of the remaining toxic substance as possible as well before it is transported into the horse’s bloodstream. Supportive measures typically include therapies such as intravenous fluids to prevent dehydration from occurring as well as combinations of electrolytes and sugars to counteract any imbalance that may arise.

There are several medications that may be recommended to alleviate the symptoms. Horses showing symptoms indicating the involvement of the heart may have antiarrhythmic drugs such as quinidine administered to regulate and slow the heart rate, after which the heart will be carefully monitored, and patients that are experiencing tremors or convulsions might be given medications such as primidone to help control them.

Recovery of Silverleaf Nightshade Poisoning in Horses

If you find this plant in pastures or near stables that your animals frequent it is best to eradicate the plant, however, Nightshade can be difficult to remove entirely due to its deep roots that tend to grow back repeatedly and even small amounts can be serious in certain circumstances as evidenced by studies in the last several years that may have uncovered a link between the ingestion of nightshade plants and subsequent toxic reactions to a popular dewormer Ivermectin. Ensuring that the fields that your horse utilizes for grazing has a large variety of appropriate grazing flora will go a long way in reducing the possibility of poisoning. In most cases, the amount eaten by horses is relatively small, and horses will recover from the poisoning swiftly, but in severe cases, it can be lethal.