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

Studies have shown that the treatment of endophyte-infected tall fescue with the broad leaf herbicide Chaparral^® can mitigate fescue toxicosis and enhance forage quality by suppressing seedhead emergence.  Application of the herbicide to fescue pastures also have shown to reduce forage mass and promote severe spot grazing when pastures are continuously grazed. A grazing experiment was conducted with steers to evaluate animal and plant responses in fescue-bluegrass mixtures treated with Chaparral to determine the effects of grazing management on pasture carrying capacity, nutritive values, botanical composition, and animal performance. Continuous and rotational (i.e., four subdivisions to provide a 7-d grazing period and a 21-d rest period) grazing treatments were assigned to six, 3.0-ha fescue-bluegrass pastures in a randomized complete block design with three replications. Each pasture had six tester steers and stocking rates were varied using put-and-take animals. Pastures were grazed from 16 April to 8 July 2013 and cattle were blocked by body weight for allotment to pastures. Rotationally grazed pastures had greater mean carrying capacity and stocking rate (P < 0.001) than continuously grazed pastures. Steers on rotationally grazed pastures had greater (P < 0.05) average daily gain and gain per acre than those on the continuous treatment. Canopies of continuously grazed pastures contained less tall fescue and greater bluegrass than those in rotationally grazed pastures. Herbage in pre-grazed paddocks had less NDF and ADF than post-grazed paddocks and continuously grazed pastures. Treatment by sample date interaction (P < 0.01) for IVDDM reflected greater declines over dates for post-grazed paddocks and continuously grazed pastures. Crude protein was not affected by treatment (P > 0.05), but consistently declined over sample dates across all treatments (P < 0.001). Results indicate that rotational grazing of Chaparral treated fescue-bluegrass mixtures can improve both animal performance and pasture productivity.