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This article in CS

  1. Vol. 52 No. 2, p. 960-969
    Received: July 25, 2011

    * Corresponding author(s): glen.aiken@ars.usda.gov
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Steer and Plant Responses to Chemical Suppression of Seedhead Emergence in Toxic Endophyte-Infected Tall Fescue

  1. Glen E. Aiken *a,
  2. Ben M. Goffb,
  3. William W. Wittb,
  4. Isabelle A. Kagana,
  5. Byron B. Sleughc,
  6. Patrick L. Burchd and
  7. F. Neal Schricke
  1. a USDA-ARS Forage-Animal Production Research Unit, Univ. of Kentucky Campus, Lexington, KY, 40546-0091
    b Dep. of Plant and Soil Sciences, Univ. of Kentucky, Lexington, KY 40546-0312
    c Dow AgroSciences, Western Research Center, Fresno, CA 93706
    d Dow Agrosciences, Christiansburg, VA 24073
    e Animal Science Dep., Univ. of Tennessee, Knoxville, TN 37996-4574. Mention of trade names or commercial products in the article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA


Chaparral herbicide has been shown to suppress seedhead emergence in tall fescue [Lolium arundinaceum (Schreb.) Darbysh] and potentially mitigate the effects of fescue toxicosis. A two-year grazing experiment evaluated steers grazed on endophyte-infected fescue–Kentucky bluegrass (Poa pratensis L.) pastures either treated or untreated with Chaparral herbicide to determine if seedhead suppression alleviates fescue toxicosis and increases average daily gain (ADG). Treatments were assigned to six, 3.0-ha fescue-bluegrass pastures in a randomized complete block design with three replications. Pastures were grazed with 48 steers (2.7 steers ha−1) from 9 Apr. to 1 July 2009 and 6 Apr. to 7 July 2010. Reproductive tiller densities in treated pastures were low in both years (<7 m−2) in comparison with untreated pastures (113 and 69 tillers m−2 in 2009 and 2010, respectively). Ergovaline and ergovalinine concentrations were three- to sixfold greater in seeds than in leaf blades and sheaths of vegetative and reproductive tillers. Crude protein, water soluble carbohydrates, and in vitro digestible dry matter concentrations of tillers declined over time at a greater rate in untreated than in treated pastures. Steers on treated pastures had greater (P < 0.01) ADG, lower (P < 0.10) rectal temperatures, and greater (P < 0.01) serum prolactin concentrations. Results indicated that Chaparral herbicide can suppress reproductive development of fescue to increase ADG and reduce the severity of toxicosis.

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