Nightshade plants (Solanaceae) consist of over 70 different species of flowering plants. Nightshades are native to North America and range from weedy shrubs to small trees. They are considered weeds and often found growing in cultivated fields, gardens, waste places and overgrazed pastures. Nightshade plants are one of the more common contaminants in poor quality hay.
Nightshade Toxic Components
Nightshade plants contain Solanaceae alkaloids, also known as glycoalkalids. Solanaceae alkaloids have significant effects on the horse's nervous system and gastrointestinal tract. Ingestion of nightshade plants--fresh or dried form, often causes variable signs of colic within a couple hours of eating the plant. Possible symptoms after horses ingest nightshade include acute hemorrhage, gastroenteritis, weakness, excess salivation, dyspnea, trembling, progressive paralysis, prostration, and death. Toxicity is highest in green berries, followed by red or black berries, leaves, stems and roots. It is estimated that 1 to 10 pounds of ingested plant material is fatal to horses.
Most horses will not eat nightshade plants unless they are very hungry with no other feed source present. It can however often be found in baled hay, which increases the chances of horses consuming it. Nightshades are still toxic, even in dried form. Nitrates can also accumulate in the plant material
What Nightshades Look Like
The flowers are five-lobed and are white or purple flowers which form fleshy green berries or fruits which turn yellow or black once matured. The leaves or alternate or opposite, hairy or smooth, and some have prominent spines. Nightshade species that have been implicated as a cause of previous poisoning incidents in horses include:
- Black nightshade (Solanum nigrum)
- Bittersweet nightshade (Solanum dulcamara)
- Silver-leaf nightshade (Solanum elaeagnifolium)
- Tropical soda apple (Solanum viarum Dunal)
- Common or American nightshade (Solanum americanum)
- Horse or bull nettle, Carolina horsenettle (Solanum carolinense)
- Hairy nightshade (Solanum physalifolium)
- Jimsonweed (Datura spp.)
- Green tomato and potato vines (Lycopericon esculenium)
- Day Jessamine (Cestrum diurnum)