Animal and Pasture Responses to Grazing Management of Chemically Suppressed Tall Fescue in Mixed Pastures.

Treatment of toxic endophyte-infected tall fescue [Lolium arundinaceum (Schreb.) Darbysh] with metsulfuran-methyl {Methyl 2-[[[[(4-methoxyl-6- methyl-1,3,5-triazin-2-yl)-amino]carbonyl]amino] sulfonyl] benzoate}, as delivered by Chaparral herbicide (Dow AgroSciences, Indianapolis, IN) can mitigate fescue toxicosis and enhance forage nutritive value by suppressing seedhead emergence. A grazing experiment was conducted with steers (2013) and heifers (2014) to evaluate animal and plant responses to grazing management of mixed cool-season grass pastures treated with Chaparral. Continuous and rotational stocking treatments were assigned to six, 3.0-ha pastures in a randomized complete block design with three replications in 2013 and two replications in 2014. Each pasture had six tester animals, and stocking rates were varied using put-and-take animals. Pastures were grazed from 16 April to 8 July 2013 and 20 May to 12 Aug. 2014. Pasture carrying capacity was 20% greater for rotational than continuous stocking. Calves on rotationally stocked pastures also had 26% greater average daily gain (ADG) and body weight (BW) gain per hectare than those on the continuous treatment. Pre-grazed herbage had less neutral detergent fiber (NDF) and acid detergent fiber (ADF) than post-grazed herbage and herbage from continuously stocked pastures in 2013, but they did not differ in 2014. Crude protein (CP) was lower in post-graze rotational pasture than in continuous or pre-graze rotational pasture. Fescue roots in rotationally stocked pastures had greater water soluble carbohydrates (WSC) and N concentrations than continuously stocked pastures following the second year of grazing. Results indicated that rotational stocking of Chaparral treated mixed pastures can improve animal performance and pasture productivity. [ABSTRACT FROM AUTHOR]