Animal and pasture responses to grazing management of chemically suppressed tall fescue in mixed pastures

Authors: WILLIAMSON, JESSICA - Pennsylvania State University; Aiken, Glen; FLYNN, SCOTT - Dow Agrosciences; BARRETT, MIKE - University Of Kentucky

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2016
Publication Date: 7/28/2016
Citation: Williamson, J., Aiken, G.E., Flynn, S., Barrett, M. 2016. Animal and pasture responses to grazing management of chemically suppressed tall fescue in mixed pastures. Crop Science. doi: 10.2135/cropsi2016.04.0206.

Interpretive Summary: A fungal endophyte found in tall fescue produces ergot alkaloids that negatively affect the performance and physiology of grazing animals. Signs of fescue toxicosis in cattle include the maintaining of rough hair coats in the summer, elevated body temperatures, labored breathing, reduced prolactin concentrations, unthrifty appearance, and poor performance. It is estimated that a combined loss of all grazing livestock industries in the USA that could be affected by endophyte-infected tall fescue exceeds one billion dollars annually. Recent studies have evaluated the use of the herbicide active ingredient, metsulfuran-methyl, for inhibiting the emergence of tall fescue seedheads emergence in tall fescue, which alleviates the seedheads as a source of toxins and allows the grass to remain in a vegetative, more nutritious stage of growth. Animals grazing metsulfuran-methyl treated fescue pastures exhibit greater ADG and exhibit less severe fescues toxicosis. A benefit of chemical seed head suppression of tall fescue was indicated to be through the alleviation of toxic seedheads and enhanced nutritive value by maintaining fescue in a vegetative stage of growth; however, the number of cattle the pastures support can be reduced. A grazing experiment compared between continuous and rotationally stocked pastures determined that implementing a rotation system for chemically seedhead suppressed pastures of toxic endophyte-infected tall fescue can enhance steer average daily weight gain, weight gain per hectare, and pasture productivity. Rotational stocking should be recommended to improve the sustainability of chemically suppressed tall fescue pastures.

Technical Abstract: Treatment of toxic endophyte-infected tall fescue [Lolium arundinaceum (Schreb.) Darbysh] with metsulfuran-methyl 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 2 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 capacities were 20 percent greater for rotational than continuous stocking. Calves on rotationally stocked pastures also had 26 percent greater average daily gain and body weight gain per ha than those on the continuous treatment. Herbage in pre-grazed paddocks had less neutral detergent fiber and acid detergent fiber than post-grazed paddocks and continuously grazed pastures in 2013, but did not differ in 2014. Crude protein 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 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.