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Fungal Populations in the Rumen Associated with Fescue Toxicosis¹

ABSTRACT

The fungal population of the rumen of fistulated steers grazing fescue (Festuca arundinacea Schreb.) was studied in 1972 and 1973. Aspergillus terreus Thom was found in 1972 in the rumen shortly after the steers were placed on fescue pastures. Populations of this fungus increased in 6 weeks from 0 to over 1000 propagules per gram of rumen fluid. One month after the steers were placed on this pasture, fescue toxicosis occurred. Aspergillus terreus was not found in the rumen of fistulated steers grazing fescue in 1973, and no fescue toxicosis developed in these steers. Fusarium tricinctum (Cda.) Sacc. and other fungi were found in both years but not in high populations as was A. terreus. In 1972 A. terreus was isolated from fescue in four different counties in Mississippi where fescue toxicosis was found. In 1973 no A. terreus was isolated from these same fields and no fescue toxicosis occurred. Higher numbers of propagules of A. terreus were found in 1972 in fescue growing on low nitrogen. Two out of three fistulated steers artifically dosed with A. terreus and grazing fescue in 1973 developed swollen and tender feet, symptoms of fescue toxicosis. Aspergillus terreus remained viable through the entire digestive tract of these three steers in 1973.

Key Words: Aspergillus terreus • Fusarium tricinctum • fungal propagule • fungal mycoplasm • rumen content • fistulated steers • digestive tract

¹ Contribution from the Agricultural Research Service, USDA and Technical Article no. 2610 of the Mississippi Agr. & Forestry Exp. Sta., Mississippi State, Miss. 39762.

² Research Plant Pathologist, ARS and Professor of Field Crop Diseases; Professor and Head of the Department of Veterinary Science; Associate Biochemist; Associate Agronomist; and Assistant to Director, Miss. Agr. & Forestry Exp. Sta.

Received for publication June 22, 1973.