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What is Bittersweet Nightshade Poisoning?

All parts of the bittersweet nightshade plant are toxic to horses. The seeds, berries and leaves have the highest levels of the toxin solanine. Solanine is a toxic alkaloidal glycoside that is found in nightshade varieties and green potatoes. 

Like with other varieties of nightshade, the bittersweet nightshade is naturally distasteful to horses. Most horses will avoid eating this plant unless there is limited forage in their pasture. Bittersweet nightshade remains toxic when dried and has sometimes been found in hay.

Bittersweet nightshade, or solanum dulcamara, is a climbing vine that has simple leaves that can have lobes near their base and bluish purple or deep purple flowers. It can reach six feet in length. Bittersweet nightshade has berries that are green when unripe that turn red when ripe. The berries will stay on the vines through mid-winter. Some people refer to bittersweet nightshade as European bittersweet or climbing nightshade.

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Symptoms of Bittersweet Nightshade Poisoning in Horses

It is important that you seek immediate veterinary care when you suspect that your horse has ingested bittersweet nightshade. Your horse’s recovery will depend on how quickly treatments begin. If you notice any of these symptoms, remove your horse from their pasture and do not give any food until your veterinarian completes an assessment.

  • Anorexia
  • Dilated pupils
  • Abdominal pain
  • Irritated throat
  • Dry mouth
  • Sensitivity to light
  • Irregular heart rate
  • Nervousness or hyper-excitability
  • Muscle tremors or convulsions
  • Constipation or diarrhea
  • Disorientation
  • Ataxia or loss of coordination
  • Excessive lying down or recumbency
  • Convulsions 
  • Death 

Causes of Bittersweet Nightshade Poisoning in Horses

Most horses will avoid bittersweet nightshade when there is plenty of other forage for them in their pasture. When the pasture is sparse, then they may willingly eat the plant. Otherwise, bittersweet nightshade poisoning will occur when the seeds, berries or leaves fall into the grass of their pasture and they ingest them or the plant is mixed in with their feed, such as in their hay. 

Every part of the bittersweet nightshade plant is toxic to horses when ingested. The leaves, berries and seeds hold the highest concentration of the toxin solanine which is an alkaloidal glycoside. An alkaloidal glycoside is a toxin that has at least one sugar molecule linked to an oxygen molecule and oftentimes a nitrogen based molecule. The substance becomes toxic when the sugar molecule is taken away, usually during the process of digestion.

Diagnosis of Bittersweet Nightshade Poisoning in Horses

There are no specific tests available to conclusively diagnose bittersweet nightshade poisoning in your horse. Your veterinarian will begin by asking you about the symptoms that you have seen. They will also ask you about your horse’s feed, hay and forage within their pasture. Samples of various plants in their pasture and their hay may also be taken for analysis. 

A full physical examination will also be done; your veterinarian may pay special attention to your horse’s mouth. They will be searching for any plant matter that may still be present in the mouth or stuck in the teeth. If there is plant matter present, a sample will be collected.

A complete blood count, or CBC, urinalysis and fecal examination will be conducted. These will rule out other possible causes for your horse’s illness. A clinical chemistry analysis may also be completed.

Treatment of Bittersweet Nightshade Poisoning in Horses

Once your veterinarian has diagnosed bittersweet nightshade poisoning in your horse, treatments will begin immediately. Your veterinarian may suggest that your horse be hospitalized for a few days until they see how well your horse responds to the treatments. This will allow for supportive care to be administered and constant monitoring can be done.

There are no known medications that will counteract the toxin, solanine. Some veterinarians may opt to try neostigmine, a medication that is used in deadly nightshade poisoning, but there is no evidence that this medication actually works in bittersweet nightshade poisoning. 

Activated charcoal, given orally, will help absorb any of the toxins that are still in the stomach. Intravenous fluids and nutrition therapy will be administered during treatments. Your veterinarian will treat the symptoms as they present.

Recovery of Bittersweet Nightshade Poisoning in Horses

Death can occur in severe cases of bittersweet nightshade poisoning or if veterinary care is not sought quickly once symptoms present. Generally, with aggressive treatments, your horse will make a full recovery.

Practice good pasture maintenance and be aware of the plants that are growing on your property, especially those plants in or near your horse’s pasture. Eradicate any plants that may be poisonous to your horse. A pasture safe herbicide can be used to completely eliminate poisonous plants and weeds.