Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2012
Publication Date: 1/28/2015
Citation: Aiken, G.E., Strickland, J.R. 2015. Managing the tall fescue-fungal endophyte symbiosis for optimum forage-animal production. Journal of Animal Science. 91(5):2369-2378.
Interpretive Summary: Agronomic traits of tall fescue attributed to the toxic endophyte has resulted in this endophyte-grass being widely utilized in a large region of the USA, but ergot alkaloids produced by the endophyte induce a toxicosis that adversely affects cattle performance and well being. Management approaches can be used to improve cattle production on toxic endophyte tall fescue and mitigate or alleviate the symptoms of toxicosis. Continuous, intensive grazing of toxic endophyte tall fescue can reduce alkaloid toxicity of the tall fescue, but high inputs of fertilizer and weed control will be necessary for pastures to be sustainable. Recent development of tall fescue cultivars artificially infected with novel endophytes that do not produce ergot alkaloids is the only technology currently available to alleviate fescue toxicosis but grazing management must be modified during periods of low forage growth. The highly toxic seed heads that are readily grazed by cattle can be suppressed with metsulfuron containing herbicides to improve animal performance, but grazing management will be needed to accommodate for a reduction in forage production. Vulnerability to severe heat stress also can be avoided by moving cattle to warm-season grass pastures during the late spring and summer. Dilution of ergot alkaloids by interseeding legumes or feeding supplements has been recommended, but sensitivity of cattle to ergot alkaloids and bioaccumulation of the alkaloids in cattle tissues appear to limit effectiveness of ergot alkaloid dilution in alleviating toxicosis. These management approaches provide options to cattle producers in “managing around” fescue toxicoxis. Other technologies and approaches could also be developed in the future as more basic research is conducted to better understand effects of ergot alkaloids at the cellular and molecular levels.
Technical Abstract: Alkaloids produced by the fungal endophyte (Neotyphodium coenophialum) that infects tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] are a paradox to cattle production. While certain alkaloids impart tall fescue with tolerances to environmental stresses, such as moisture, heat, and herbivory, ergot alkaloids produced by the endophyte can induce fescue toxicosis, a malady that adversely affects animal production and physiology. Hardiness and persistence of tall fescue under limited management can be attributed to the endophyte, but the trade-off is reduced cattle production from consumption of ergot alkaloids produced by the endophyte. Improved understanding and knowledge of this endopyte-grass complex has facilitated development of technologies and management systems that can either mitigate or completely alleviate fescue toxicosis. This review discusses the research results that have led to development of 5 management approaches to either reduce the severity of fescue toxicosis or alleviate it altogether. Three approaches manipulate the endophyte-tall fescue complex to reduce or alleviate ergot alkaloids: 1) use of heavy grazing intensities, 2) replacing the toxic endophyte with non-ergot alkaloid producing endophytes, and 3) chemical suppression of seed head emergence. The remaining 2 management options do not affect ergot alkaloid concentrations in fescue tissues, but are used to: 1) avoid grazing of tall fescue with high ergot alkaloid concentrations in the late spring and summer by moving cattle to warm-season grass pasture, and 2) dilute dietary alkaloids by interseeding clovers or feeding supplements. A review of the development of these managements will be discussed.