Tall fescue toxicosis is a frequent disorder in cattle grazing endophyte [Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin] infested tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]. Signs of tall fescue toxicosis in beef cattle include decreased milk production, birth weight and weight gains, pregnancy rate and serum prolactin levels, and increased respiration rate. ‘Kentucky 31' (KY-31) tall fescue infested with the endophytic fungus (E+) is the predominant fescue cultivar grown in the mid-southern United States. It supplies most of the nutrients needed by more than 20% of U.S. beef cattle herds. Research on E+ tall fescue has focused on identifying the presence of the endophyte and associated alkaloids (livestock toxins) and the effects of alkaloids on grazing animals. Reduced reproductive rates associated with ingesting E+ tall fescue occur either at ova fertilization or within the first 7 d following fertilization. Stocker cattle grazing E+ tall fescue have reduced weight gain and reduced ability to dissipate heat during summer. The most visible sign of toxicosis is retained winter haircoat into late spring and summer. Nutrient composition of forage is similar regardless of the endophyte status. Reduced animal performance is linked to decreased nutrient intake and the effects of the alkaloids ingested. Removing the endophyte from the infested plants created endophyte free (E-) plants and improved cattle performance, but the plants did not persist under normal grazing and environmental conditions. Recently, non-ergot alkaloid producing endophytes have been inserted into elite tall fescue cultivars. These tall fescue-novel endophyte combinations have improved animal performance similar to that of E- tall fescue and have persistency consistent with that of E+ tall fescue.
Keywords: Neotyphodium coenophialum, tall fescue, toxicosis.
Abbreviations: ADF, acid detergent fiber; ADG, average daily gain; CP, crude protein; DM, dry matter; DMD, dry matter digestibility; DMI, dry matter intake; E-, endophyte free, free of Neotyphodium; E+, infected by wild Neotyphodium endophyte; NDF, neutral detergent fiber; OM,, organic matter.
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