Potential for hydrocyanic acid poisoning of livestock by indiangrass

Abstract

Hydrocyanic acid or prussic acid poisoning of livestock by sorghums [Sorghum bicolor (L.) Moench] and sudangrasses [Sorghum sudanese (Piper) Stapf] is caused by the digestive liberation of hydrocyanic acid (HCN) from the cyanogenic compound, dhurrin [(S)-p-hydroxymandelonitrile β-D-glucopyranoside] found in tissue of these plants. Recent research documented that dhurrin is also present in indiangrass [Sorghastrum nutans (L.) Nash] seedlings. The purpose of this study was to determine the hydrocyanic acid potential (HCN-p) of forage from established stands of indiangrass. Five cultivars representative of indiangrass germplasm of the Great Plains were sampled during the growing season for 2 years from 2 sites in eastern Nebraska. The HCN-p of the indiangrass sampled in this study exceeded 750 mg-1 kg dry wt. (dangerous level) only in spring when new growth was 20 cm tall or less. Levels were less than 500 mg-1 kg (safe) when new growth was at least 40 cm tall and were very low (<200 mg-1 kg) or not detected when the forage was over 1 m tall. Pure stands of indiangrass that are grazed when the new growth is less than 20 cm tall could be lethal to livestock.