loids derived from the endophyte association (Hill et al., 1994), which causes poor weight gain and reproduc-For tall fescue (Festuca arundinacea Schreb.) in the southeastern tion in afflicted animals (Hoveland et al., 1983(Hoveland et al., , 1997 USA, persistence and yield are directly related to infection with a fungal endophyte [Neotyphodium coenophialum (Morgan-Jones & Stuedemann and Thompson, 1993). Ergovaline is con-Gams.) Glenn, Bacon, & Hanlin comb. nov.]. However, most endo-sidered the main ergot alkaloid responsible for most phyte-infected (Eϩ) tall fescue cultivars produce toxic ergot alkaloids animal problems (Lane, 1999). resulting in poor weight gain and reproduction in grazing livestock. Summer drought results in the greatest loss of tall The objective of this paper was to assess the strategy of reinfecting fescue stands in the Southeast, with cultivars infected 'Jesup' and 'Georgia 5' tall fescue with non-ergot alkaloid-producing with their endemic N. coenophialum endophyte demonendophyte strains. Different cultivar-strain combinations were tested strating much better survival in very hot, dry summers against the Eϩ and endophyte-free (EϪ) versions of the same cultivars than the same cultivars with their endophyte removed for stand survival and dry matter yield; in separate experiments, they (Bouton et al., 1993a). Therefore, the toxicity of Eϩ were assessed for toxicity in lambs (Ovis aries ). Most cultivar-strain tall fescue presents livestock producers with a dilemma combinations produced no ergot alkaloids but varied in ability to transmit through seed. The best combination, Jesup (AR542), pos-of whether to grow current Eϩ cultivars for stand persissessed yield and stand survival better (P Ͻ 0.05) than the EϪ checks tence and risk reduced animal performance due to the and equivalent (P Ͻ 0.05) to the Eϩ checks. Lambs gained an average inherent toxins. of 124 g/d on both cultivars containing AR542, which was equivalentAnimal toxicity can be reduced in current Eϩ pasto gains on EϪ forage but approximately 57% greater than gains tures with pasture management such as interplanting on Eϩ forage. Animals consuming forage from EϪ or non-ergotwith clovers to dilute the toxins directly in the forage producing strains did not exhibit depressed serum prolactin or elebefore consumption (Ball, 1997) or controlling of toxicovated body temperatures of animals on Eϩ forage. The strategy of sis directly in the animals with drugs, vaccines, feed reinfecting tall fescue cultivars with naturally occurring, non-ergotadditives, or detoxification agents (Oliver, 1997; Stuedeproducing endophytes appears promising for removing toxicity sympmann and Thompson, 1993). Cultivar improvement to toms and retaining agronomic performance, but intense screening is needed to identify the best cultivar-strain combinations. Program. Received

loids derived from the endophyte association (Hill et al., 1994), which causes poor weight gain and reproduc-For tall fescue (Festuca arundinacea Schreb.) in the southeastern tion in afflicted animals (Hoveland et al., 1983(Hoveland et al., , 1997 USA, persistence and yield are directly related to infection with a fungal endophyte [Neotyphodium coenophialum (Morgan-Jones & Stuedemann and Thompson, 1993). Ergovaline is con-Gams.) Glenn, Bacon, & Hanlin comb. nov.]. However, most endo-sidered the main ergot alkaloid responsible for most phyte-infected (Eϩ) tall fescue cultivars produce toxic ergot alkaloids animal problems (Lane, 1999). resulting in poor weight gain and reproduction in grazing livestock. Summer drought results in the greatest loss of tall The objective of this paper was to assess the strategy of reinfecting fescue stands in the Southeast, with cultivars infected 'Jesup' and 'Georgia 5' tall fescue with non-ergot alkaloid-producing with their endemic N. coenophialum endophyte demonendophyte strains. Different cultivar-strain combinations were tested strating much better survival in very hot, dry summers against the Eϩ and endophyte-free (EϪ) versions of the same cultivars than the same cultivars with their endophyte removed for stand survival and dry matter yield; in separate experiments, they (Bouton et al., 1993a). Therefore, the toxicity of Eϩ were assessed for toxicity in lambs (Ovis aries ). Most cultivar-strain tall fescue presents livestock producers with a dilemma combinations produced no ergot alkaloids but varied in ability to transmit through seed. The best combination, Jesup (AR542), pos-of whether to grow current Eϩ cultivars for stand persissessed yield and stand survival better (P Ͻ 0.05) than the EϪ checks tence and risk reduced animal performance due to the and equivalent (P Ͻ 0.05) to the Eϩ checks. Lambs gained an average inherent toxins. of 124 g/d on both cultivars containing AR542, which was equivalent Animal toxicity can be reduced in current Eϩ pasto gains on EϪ forage but approximately 57% greater than gains tures with pasture management such as interplanting on Eϩ forage. Animals consuming forage from EϪ or non-ergotwith clovers to dilute the toxins directly in the forage producing strains did not exhibit depressed serum prolactin or elebefore consumption (Ball, 1997) or controlling of toxicovated body temperatures of animals on Eϩ forage. The strategy of sis directly in the animals with drugs, vaccines, feed reinfecting tall fescue cultivars with naturally occurring, non-ergotadditives, or detoxification agents (Oliver, 1997; Stuedeproducing endophytes appears promising for removing toxicity sympmann and Thompson, 1993). Cultivar improvement to toms and retaining agronomic performance, but intense screening is needed to identify the best cultivar-strain combinations.

Grazing studies were conducted to determine cattle growth performance, evaluate toxicosis, and compare grazing behavior in stocker cattle grazing nonergot alkaloid-producing endophyte-infected (AR542 or AR502), endophyte-free (E-), or wild-type toxic endophyte-infected (E+) Jesup, Georgia-5, and Kentucky-31 tall fescue. Replicated 0.81-ha tall fescue paddocks were established at the Central Georgia Branch Station at Eatonton and the Northwest Georgia Branch Station at Calhoun during October 1998 and were stocked with beef cattle for autumn and spring periods from fall 1999 through spring 2002. Mean ergot alkaloid concentrations were higher (P < 0.01) on E+ pastures than the other treatments at both locations. At Calhoun and Eatonton, post-treatment serum prolactin concentrations were decreased (P < 0.01) on E+ compared with AR542, AR502, and E- tall fescue. Cattle on AR542, AR502, and E- pastures had lower (P < 0.05) post-treatment rectal temperatures than cattle grazing E+ tall fescue during spring at Eatonton and Calhoun. Calf ADG was higher (P < 0.05) on AR542, AR502, and E- as compared with E+ tall fescue during autumn and spring grazing at Eatonton, and at Calhoun, cattle on E+ pastures had lower (P < 0.05) ADG in both autumn and spring. Gain/hectare was higher (P < 0.05) on AR542, AR502, and E- than on E+ during autumn at Eatonton and during spring at both locations. In autumn at Calhoun, gain/hectare was greater (P < 0.05) on AR502 and E- compared with E+ tall fescue. During April, May, and June, cattle grazing E+ pastures at Eatonton spent more (P < 0.01) time idling, more (P < 0.01) time standing, and used more (P < 0.01) water than cattle on AR542 and E- tall fescue. Daily prehensions and biting rate were each higher (P < 0.01) on AR542 and E- tall fescue than E+ tall fescue in both grazing seasons. There were no differences among pasture treatments for bite size in either spring (P = 0.50) or autumn (P = 0.34). Steers grazing E+ pastures had lower DMI than steers grazing AR542 and E- pastures during spring (P < 0.10) and lower DMI than steers grazing E- pastures during autumn (P < 0.05). Daily steer water usage was decreased (P < 0.10) in E+ pastures compared with AR542 and E- pastures during late fall. These results indicate that nonergot alkaloid-producing endophyte technology is a promising option for alleviating tall fescue toxicosis in stocker cattle.

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