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Effects of Feeding Kentucky 31 Tall Fescue Seed Infected with Acremonium Coenophialum to Laboratory Rats

Auburn University⁴, AL 36849

Abstract

An endophytic fungus found in Kentucky 31 (KY-31) tall fescue has been associated with the "summer syndrome" (fescue toxicity) in grazing cattle. Four experiments were conducted to investigate the use of weanling rats as an animal model to study the fescue toxicity syndrome. When graded levels of fungus-infected (INF) or fungus-free (FF) KY-31 seed were fed, feed intake and growth rates were inversely related to the amount of INF seed in the diet. When diets containing 50% seed were fed, rats eating INF seed had reduced (P<.05) daily water consumption (9 vs 20 ml) and lowered (P<.05) body temperatures (36.8 vs 37.7 C) when compared with the FF treatments. Autoclaving the seed increased feed intake and growth rate of rats receiving both INF and FF seed diets, but daily gains continued to be less (P<.05) in the rats fed autoclaved INF diets when compared with rats fed autoclaved FF diets (2.3 vs 6.8 g). Rats fed diets containing either 40% shredded wheat on which the fescue endophyte had been grown or 40% shredded wheat that was not innoculated did not differ in performance. Crude fiber, nitrogen-free extract, gross energy and dry matter digestibilities were enhanced (P<.05) by the presence of INF seed in the diets when compared with the FF seed treatments. Crude protein and ether extract digestibilities and apparent biological value of fescue protein were not affected by presence of the fungus. The effect of INF seed on organ weights was inconsistent. There were no histopathological changes seen in response to consumption of INF seed. Fungus-infected seed used in these experiments contained greater concentrations of loline alkaloids (5,134 vs 652 µg/g) than the FF seed.

¹ Contribution from the Alabama Agr. Exp. Sta. Journal Series No. 4-84711.

² The authors would like to express their appreciation to Dr. L. P. Bush, Dept. of Agron. at the Univ. of Kentucky, for performing the alkaloid analysis of the seed used in this study.

³ A special thanks is extended to Steve Jungst for technical assistance in data analysis and programming, to Dr. N. D. Davis for providing assistance in the isolation and identification of Acremonium coenophialum in our fescue seed, and to Dr. F. E. Mitchell, Alabama Veterinary Diagnostic Laboratory, for the gross and histological examination of organs.

⁴ Dept. of Anim. and Dairy Sci., Alabama Agr. Exp. Sta.