Because the alkaloids act on the nervous system, bodily functions are affected. Animals may have dilated pupils, become agitated, have increased heart rate, tremble, become delirious, appear to be hallucinating, have convulsions, become comatose, and possibly die. The plant grows in dense stands, reaches heights up to 8 feet in some situations and often has reddish brown blotches on its leaves. The seed heads are large, open and loose. The young shoots are the most toxic, and when wilted or frost-damaged, cyanide becomes readily available in the leaves.
Nitrates can also accumulate in johnsongrass.
Well-cured hay is relatively safe for animal consumption as mature plants have much lower toxicity. The animal will breathe rapidly and deeply, then become anxious and stressed. Progressing symptoms include trembling, incoordination, attempts to urinate and defecate and collapsing. Finally, respiratory or cardiac arrest may occur, leading to a violent death. Most have a thick, milky sap in their leaves, stems and seedpods.