Dr. A. Morrie Craig and Dr. Linda L. Blythe
College of Veterinary Medicine
Oregon State University
Fescue foot, summer syndrome, and ryegrass staggers are all diseases of livestock related to endophyte toxins in pasture grasses. Range finding experiments and case studies of fescue foot and perennial ryegrass staggers (PRGS) were conducted on cattle and sheep under grazing and barn conditions. The main objective was to determine threshold levels of the endophyte toxins, ergovaline and lolitrem B, associated with the diseases of fescue foot and ryegrass staggers, respectively.
Clinical disease of fescue foot was produced with 825 ppb dietary ergovaline in a period of 42 days in cattle but not in sheep. Field and barn studies of natural fescue foot in a herd of sheep were conducted and clinical disease was not seen at 1215 ppb.
Lolitrem B toxin at 2135 ppb in perennial ryegrass was associated with clinical cases of ryegrass staggers in 42 of 237 sheep (18% residue rate) in the Willamette Valley of western Oregon. These were the first range finding experiments undertaken in this locale to document threshold levels of endophyte toxins associated with fescue foot and PRGS.
CONCLUSIONS: THRESHOLD LEVELS FOR FESCUE TOXICOSIS AND
PERENNIAL RYEGRASS STAGGERS
With the scientific knowledge available as 2001, toxicosis is induced in livestock as follows.