Submitted to: Kentucky Forage and Grassland Council
Publication Type: Proceedings
Publication Acceptance Date: 9/29/2009
Publication Date: 10/29/2009
Citation: Aiken, G.E. 2009. Tall Fescue Grazing Research. Kentucky Forage and Grassland Council.
Interpretive Summary: Tall fescue owes its persistence and productivity in large part to a fungal endophyte that infects most plants. This endophyte produces an array of alkaloids that benefit the plant in tolerating heat, drought, and grazing. Unfortunately, the endophyte also produces ergot alkaloids that can cause “fescue toxicosis” in cattle. Cattle inflicted with toxicosis have reduced dry matter intake, elevated body temperature, and often retain their winter hair coats in the summer. Weight gain by yearling cattle can be very poor (< 1.0 lb/day) and calving percentages of cow herds can be substantially reduced. Endophyte-free varieties were commercially released in the 1980s, but proved to lack persistence in pastures; however, other approaches have been developed to manage around fescue toxicosis. Cattle performance on endophyte-infected tall fescue can be at acceptable levels if ergot alkaloids in the diet are diluted by interseeding clovers, or by feeding concentrates or by-product feeds. Another alternative is by planting tall fescue varieties infected with novel endophytes that do not produce ergot alkaloids and therefore are not toxic (as opposed to the wild type endophyte in Kentucky-31 tall fescue that produces toxic concentrations of ergot alkaloids). AgResearch Ltd. (New Zealand) successfully patented seven strains of tall fescue novel endophytes. Following grazing evaluations by the University of Georgia of tall fescue host (genotype) and novel endophyte combinations, the AR542 novel endophyte strain was inserted in Jesup and ‘Georgia-5’ and marketed as MaxQ®. An update is provided on research that has evaluated cattle performance and physiology of cattle grazing novel endophyte tall fescue, and persistence and productivity of novel endophyte tall fescue under long-term grazing.
Technical Abstract: Tall fescue is a cool-season perennial grass that is well adapted in the upper transition zone between the temperate northeast and subtropical southeast. Its adaptation in the “fescue belt” is primarily due to a fungal endophyte that imparts tolerance to drought, heat, and grazing stresses. Unfortunately, ergot alkaloids produced by the endophyte cause a toxicosis in grazing livestock. Cattle exhibiting fescue toxicosis are vasoconstrictive (regardless of prevailing ambient temperature), retain rough hair coats into the summer, and have reduced dry matter (DM) intake. Natural endophytes that do not produce ergot alkaloids have been collected by plant exploration for screening and development of novel endophytes. Grazing experiments have shown similar animal performance and well-being between multiple novel endophyte-infected and endophyte-free tall fescues. These experiments also showed that novel endophyte-infected tall fescue can persist under grazing. Results of these experiments are reviewed to evaluate performance and physiology of cattle grazing novel endophyte tall fescue, and stand persistence and productivity of novel endophyte tall fescue under long-term grazing.