Submitted to: American Forage and Grassland Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/26/2011
Publication Date: 6/12/2011
Citation: Aiken, G.E., Witt, B.W., Goff, B.M., Kagan, I. 2011. Chemical suppression of seedhead emergence in toxic endophyte-infected tall fescue for improving cattle weight gain and physiology. American Forage and Grassland Conference Proceedings. CDROM. Interpretive Summary: A fungal endophyte infects most tall fescue plants and produces ergot alkaloids that can induce a toxicosis. Symptoms of “fescue toxicosis” in beef cattle are elevated core body temperatures, low prolactin concentrations, and poor weight gain efficiency. Chaparral® herbicide (Dow AgroSciences LLC) applied to endophyte-infected tall fescue suppresses emergence of seedheads, which can have 4-times greater alkaloid concentrations than leaf blades. A 2-yr grazing experiment was conducted with endophyte-infected tall fescue to determine if herbicide suppression of seedheads can mitigate the negative effects of ergot alkaloids on steer weight gain and physiology. Averaged over the 2-year experiment, steers grazing herbicide-treated pastures as compared to those grazing untreated pastures had 39% greater average daily gain, reduced rectal temperatures, and a 6-fold increase in serum prolactin concentrations. Results of the experiment indicated that application of Chaparral herbicide to E+ tall fescue can suppress seedhead emergence to improve steer weight gain and reduce the severity of toxicosis.
Technical Abstract: A two-yr grazing experiment was conducted with steers grazed on endophyte-infected tall fescue pastures that were either treated or untreated with Chaparral® herbicide to determine if suppression of seedhead emergence and maturity can increase average daily gain (ADG) and alleviate fescue toxicosis. Herbicide treatments were assigned to six, 7.5-acre pastures of endophyte-infected tall fescue pastures in a randomized complete block design with 3 replications. Pastures were grazed with 48 steers (8 per pasture) from 9 April to 1 July, 2009 and 6 April to 7 July, 2010. Treated pastures were practically void of seedheads, whereas untreated pastures had 94 and 57 reproductive tillers/yd2 in 2009 and 2010, respectively. Ergovaline plus ergovalinine concentrations were 4-fold greater in seed than in leaf blades. Ergovaline concentrations in vegetative blades were similar between treated and untreated pastures in 2009, and greater in treated than in untreated pastures in 2010. Average daily gain on treated pastures was 39% greater (P < 0.05) than on untreated pastures. Steers on treated pastures had lower rectal temperatures and greater serum prolactin concentrations. Results indicated that Chaparral® herbicide treatment suppressed seedhead emergence and maturity of tall fescue pastures to increase weight gain and reduce the severity of fescue toxicosis.