Since elimination of the endophyte does not result in persistent tall fescues, a new approach has been developed whereby strains of N. coenophialum which do not result in toxicosis but do convey tolerance to pests and other stresses, are substituted for the toxic strain. Collaborative work between Bouton and coworkers in Georgia and researchers in New Zealand (see Chapter 19) resulted in the release of Jesup MaxQ tall fescue in 2000 (Bouton et al., 2002). This combination of the adapted elite tall fescue cultivar Jesup, and the non-ergot alkaloid producing endophyte MaxQ has been evaluated under grazing in Georgia with lambs (Parish et al., 2003a), stocker steers (Parish et al., 2003b), and cow-calf pairs (Watson et al., 2004). In Arkansas, West et al. (2002) inserted the non-ergot alkaloid producing endophyte Strain 4 into the tall fescue cultivar HiMag (Sleper et al., 2002) and released ‘ArkPlus'. Grazing trials measuring animal performance with steers, and the productivity and persistence of HiMag, were reported by Nihsen et al. (2004) and Beck et al. (2008). Steer prolactin levels, respiration rates, rectal temperatures, and hair scores were similar between the E- and ArkPlus tall fescues. Gunter and Beck (2004) summarized results published before 2003 on Jesup MaxQ and ArkPlus. Animal performance with the novel endophytes was similar to that with E- and consistently better than that with E+ tall fescue (Fig. 16-6 and 16-7).
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Fig. 16-6. Angus steer in July after having grazed Jesup MaxQ tall fescue since March at Knoxville, TN, in 2005. Compare appearance with that of steers in Fig. 16-7.
Fig. 16-7. Angus steers on E+ tall fescue pasture at Knoxville, TN, in July 2005.
Currently, novel endophyte cultivars are being established in most tall fescue growing regions of the United States. Cattle managers are basing the decision to establish on density of current E+ stands and their level of endophyte infestation, costs of seed and re-establishment procedures, and expected improvement in reproductive rates in cows or weight gains of stocker cattle. Zhuang et al. (2005) conducted an economic analysis of replacing existing E+ pastures with novel endophyte tall fescue. Their results indicated that the break-even infestation rate for cow-calf producers was when current pastures were more than 74% E+. Beck et al. (2008) conducted an economic analysis of a grazing study comparing novel and toxic endophyte tall fescues to cool-season annual grasses. Their results indicated that improved profitability associated with steers grazing novel endophyte pastures would require 4 yr for a new seeding to break even. Therefore, stocker operators should consider stocking rate, percent infestation, and expected animal performance when deciding whether to replace existing E+ pastures.
Taking advantage of these new tall fescue-endophyte combinations will require the destruction of current stands of E+ tall fescue and re-establishment with novel endophyte tall fescues. Andrae et al. (2003) found that intervening no-till glyphosate-resistant corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] crops, and paraquat and glyphosate fallows, were effective for renovation of existing E+ tall fescue stands (see Chapter 5).
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