The role of fungal tremorgens in ryegrass staggers

Abstract

Administration of the fungal tremorgens penitrem A, verruculogen, fumitremorgin B, and paxilline to sheep produced effects similar to signs of ryegrass staggers (RGS); fungi capable of producing tremorgens were present in the environment where RGS was occurring or had occurred; and spores of these fungi were ingested by sheep grazing the pastures. Of 23 species of Penicillium isolated from toxic pastures, 2 common species produced tremorgens: P. crustosum produced penitrem A and P. piscarium produced either verruculogen or verruculogen and fumitremorgin B. Each of these species was isolated from ryegrass, from soil, and from dung of affected animals. When cultured and fed to sheep they produced effects similar to signs of RGS. No direct evidence of tremorgen production in the natural habitat was obtained, nor were tremorgens detected chemically in ryegrass from toxic pastures. The observations are consistent with, but not conclusive proof of, a causative role for fungal tremorgens in RGS. The possibility of synergism between tremorgens is raised.