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ARS Home » Midwest Area » Lexington, Kentucky » Forage-animal Production Research » Research » Publications at this Location » Publication #285283
Title: Chemical suppression of seed head emergence in toxic endophyte-infected tall fescue pastures

Author
item Aiken, Glen
item WITT, W - University Of Kentucky
item GOFF, B - University Of Kentucky
item Kagan, Isabelle

Submitted to: Kentucky Beef Report
Publication Type: Experiment Station
Publication Acceptance Date: 10/9/2012
Publication Date: 10/9/2012
Citation: Aiken, G.E., Witt, W.W., Goff, B.M., Kagan, I. 2012. Chemical suppression of seed head emergence in toxic endophyte-infected tall fescue pastures. Kentucky Beef Report. Pgs 11-12.

Interpretive Summary: Tall fescue is a cool-season perennial grass that is the predominant forage in Kentucky. A fungal endophyte infects most plants of Kentucky 31 tall fescue and produces alkaloids that impart tolerances of the grass to stresses from dry soils, heat, and grazing, but also produces ergot alkaloids that cause fescue toxicosis. Symptoms of the malady in cattle include rough hair coats during the summer, elevated body temperature, labored respiration, and decreased prolactin concentrations. Seed heads contain the highest concentrations of ergot alkaloids and cattle selectively graze this toxic source of ergot alkaloids. A two-year grazing experiment with steers determined if chemical suppression of tall fescue seed heads could increase daily weight gain and alleviate fescue toxicosis. Averaged over the 2 years, steer ADG in treated pastures was 39% higher than in untreated pastures. Serum prolactin, measured as a marker of toxicosis (low concentrations indicative of toxicosis) in steers grazing treated pastures were 2-fold greater than in those grazing untreated pastures. Lower serum prolactin in steers grazing treated pastures suggests a reduction in the severity of toxicosis for steers grazing treated pastures. Alkaloid analysis of plant tissues, however, indicated that steers on treated pastures were exposed to ergot alkaloids and likely subjected to some degree of toxicosis. Chemical suppression of tall fescue seed heads were indicated to increase daily weight gain of steers and reduce the severity of toxicosis. Managing seed heads could be used by cattle producers to improve the economic efficiency of backgrounding beef calve for the feedyard.

Technical Abstract: Results of a two-year grazing experiment with steers indicated the seed heads of toxic endophyte-infected tall fescue can be chemically suppressed to increase ADG and reduce the severity of fescue toxicosis. Six, 7.5-acre pastures of toxic endophyte-infected tall fescue pastures were either treated or untreated with Chaparral® herbicide to determine if suppression of seedhead emergence can increase average daily gain (ADG) and alleviate fescue toxicosis. Pastures were grazed with 8 steers per pasture from 9 April to 1 July, 2009 and 6 April to 7 July, 2010. Seed head densities on treated pastures were less than 10 reproductive tillers/yd2, whereas untreated pastures had 94 and 57 reproductive tillers/yd2 in 2009 and 2010, respectively. Concentrations of two ergot alkaloids combined, ergovaline and ergovalinine, were 3-fold greater in seed heads than in leaf blades. Average daily gain on treated pastures was 39% greater than on untreated pastures. Steers on treated pastures had 2-fold greater serum prolactin concentrations (i.e., low concentrations are a marker of toxicosis). Emergence of seed heads can be chemically suppressed to enhance forage quality and alleviate seed heads as a highly toxic source of ergot alkaloids.