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FORAGE & GRAZINGLANDS

Occurrence of Condensed Tannins in Wheat and Feasibility for Reducing Pasture Bloat

^a USDA-ARS, Grazinglands Research Lab., 7207 W. Cheyenne St., El Reno, OK 73036
^b Plant and Soil Sciences Dep., Oklahoma State Univ., Stillwater, OK 74078. Cooperative investigation of the USDA-ARS and Oklahoma State University. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA-ARS or Oklahoma State University

^* Corresponding author (Charles.MacKown{at}ars.usda.gov).

Bloat can be a serious problem for ruminant livestock grazing pastures of winter wheat (Triticum aestivum L.) in the southern Great Plains. Tannins in forage can reduce the incidence and severity of bloat. We measured the content and variability of total phenolics and condensed tannins (CT) in forage extracts from wheat varieties and experimental lines (ExpLines) to assess the feasibility of developing improved varieties using conventional breeding methods to give producers a choice to reduce the incidence of bloat. Forage of 16 winter wheat varieties were collected in late fall at the start of grazing. Also, late fall forage samples and regrowth from late fall clipped forage and unclipped growth before jointing were collected for 221 diverse ExpLines and four Check varieties. Among the 16 adapted winter wheat varieties significant differences for the acid-butanol but not the vanillin CT assay were observed. Among the ExpLines, significant differences in extractable total phenolics were detected (range for all samples collected, 8.9–31.5 mg tannic acid g^–1 dry wt.) and for one of the three forage collections using each CT assay. While we observed differences in CT reactive substances among the ExpLines, even the greatest equivalent amounts detected (12 mg quebracho g^–1 dry wt. and 0.67 mg epicatechin g^–1 dry wt.) are unlikely sufficient to render the forage bloat-safe. Perhaps those experimental lines with the most abundant CT levels could be used in a selection program to increase the level of CT in wheat forage.

Abbreviations: BT Exp, breeding trial experiment • CT, condensed tannin • epicatechin-eq CT, epicatechin-equivalent condensed tannin • DFR, dihydroflavanol reductase • ExpLines, experimental lines • MCW, methanol–chloroform–water • quebracho-eq CT, quebracho-equivalent condensed tannin • tannic acid-eq TP, tannic acid-equivalent total phenolics • VT Exp, variety trial experiment