At levels of 0.34 percent cyanide potential, 0.5 lb of forage could prove fatal in grazing animals (Kingsbury, 1964).
Additional concerns arise with certain species in the Poaceae due to the ability of endophytic fungi to produce toxic compounds. Cynodon dactylon (Bermuda grass) and related species produce high levels of cyanogenic glycosides, but the syndrome known as “Bermuda grass tremors” is caused by the presence of the parasitic fungus Balansia epichloe (Bacon, 1995). The fungus produces nonpeptide ergot alkaloids such as agroclavine, which produce symptoms in livestock (especially horses) ranging from muscle twitching to paralysis of the hind limbs (Bacon, 1995). Peptide-derived ergot alkaloids, based on (+)-lysergic acid, are produced by the fungus Claviceps purpurea growing on rye (Secale cereale) (Dewick, 2002). Claviceps species infect many other cereals and grasses and the risk of ergotism is therefore always present. Ergot alkaloids of the ergopeptine class, produced by infection of Festuca species by the endophyte Acremonium coenophialum, are responsible for “fescue foot,” a lameness and gangrene in the hind feet of cattle (Kellerman et al., 1988).
A disease known as “perennial ryegrass staggers” in livestock is produced by infection of Lolium perenne by Claviceps paspali (Cheeke, 1995) and Acremonium lolii (Cheeke, 1998; Garland and Barr, 1998). The toxins are complex tremorgenic mycotoxins (penitrems and lolitrems) (Cheeke, 1998) that are potent inhibitors of calcium-activated potassium channels (Cavanagh et al., 1998). The disease is characterized by tremors, severe incoordination, and collapse.
The estrogenic macrolide zearalenone is produced by the fungus Gibberella zeae (Fusarium graminearum) growing on corn (Zea mays) and has produced vulvovaginitis, especially in pigs (Cheeke, 1998).
The Polygonaceae includes the genera Fagopyrum, Rheum, Rumex, Halogeton, and Sarcobatus. Most of these contain high levels of soluble oxalates, which have caused death in livestock and humans, and also significant amounts of nitrate (Kingsbury, 1964).
Fagopyrum sagittatum (buckwheat) is cultivated as a minor grain crop, generally for milling into flour or as a forage for animals. It has produced photosensitization in humans and animals known as fagopyrism, which appears to be of the primary type rather than secondary since there is no evidence of liver damage (Kellerman et al., 1988). The photoactive pigment is probably fagopyrine, a naphthodianthrone structurally related to hypericin in St. John’s wort (Hypericum perforatum) (Kellerman et al., 1988). Many cases of buckwheat poisoning in humans are the result of an allergic reaction to the plant, and ingestion or inhalation can induce an allergenic reaction (Kingsbury, 1964).