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

Abstract

Tall fescue toxicity has been experimentally produced in cattle by an extract chemically fractioned from toxic forage. The toxic fraction represented 11% of the dry matter of hay and was essentially free of lipids and certain alkaloids. Ergot, selenium, and boron were 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 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 subclinical levels of toxicity.