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Nature of Fescue Toxicity and Progress toward Identification of the Toxic Entity¹

Department of Dairy Science, University of Kentucky, Lexington

S. G. Yates, H. L. Tookey and I. A. Wolff

Northern Regional Research Laboratory,² Peoria, Illinois

ABSTRACT

Tall fescue toxicity has been experimentally produced in cattle by an extract chemically fractioned from toxic forage. The toxic fraction represents 11% of the dry matter of hay and is essentially free of lipids and certain alkaloids. Ergot, selenium, and boron have been eliminated as causes of the toxicity. A novel bioassay utilizing tail temperature is described which may be correlated to toxicity. The nature of the syndrome has been characterized by a study of symptoms and post-mortem findings. Lameness and gangrene in cold weather may give way to elevated body temperature and respiration rate as clinical symptoms of toxicity in warm weather. A vasoconstrictor is postulated as the causative agent. The study is continuing to learn the chemical identity of the toxic agent and if poor animal performance on fescue is correlated with sub-clinical levels of toxicity.

¹ The investigation reported in this paper is from a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director.

² This is a laboratory of the Northern Utilization Research and Development Division, ARS, USDA.