One strategy to overcome fescue toxicosis is isolation of naturally occurring, nontoxic endophyte strains ("novel" strains) followed by human intervention to reinfect the best available cultivars (see Chapter 19 and Fig. 20-1) with these strains (Bouton and Hopkins, 2003; Bouton and Easton, 2005). The main commercial product resulting from this strategy at this writing is the AR542 endophyte, registered and marketed under the brand MaxQ in the United States (Bouton et al., 2002; Bouton 2007a). MaxQ is an endophyte strain that does not produce ergot alkaloids. It is currently reinfected into the Jesup (Bouton et al., 1997) tall fescue cultivar. Jesup MaxQ is therefore the main commercial "novel" product on the market today in the United States (Rolston and Agee, 2007).
Jesup MaxQ demonstrated stand survival equivalent to that of toxic E+ tall fescue, but markedly better than that of endophyte free (E-) fescue (Bouton et al., 2002). Jesup MaxQ also showed dramatic positive effects on animal performance when compared with toxic E+ tall fescue because the effect of ergot alkaloids was not expressed (Bouton et al., 2002; Parish et al., 2003a, 2003b; Watson et al., 2004). To date, all information from research trials and on-farm experiences in both the United States and Australia, where it is marketed as Jesup MaxP, indicate no animal toxicity problems.
Farmer educational programs will be critical to ensure proper management and overall success of novel endophytes (Roberts and Andrae, 2005), but economic value will be the main determinant of whether farmers will use these types of products (Bouton, 2007a). Economic returns for converting to Jesup MaxQ are highly dependent on the severity of each producer's current tall fescue toxicity problems. However, a recent report concluded that the economic value to U.S. producers for making the conversion to novel endophyte products is positive and large (Parish and Watson, 2007). The replacement of E+ tall fescue, where producers currently experience an 80% calf crop, a 20% reduction from the ideal, by Jesup MaxQ, is estimated to generate net returns of $55/cow/yr, or $36/cow/yr when the cost of establishment is included (Andrae and Lacy, 2004).
|Fig. 20-1. Building a novel endophyte-infected tall fescue by removing the toxic endophyte and then adding the novel endophyte (Hancock and Andrae, 2009).|
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