The presence of N. coenophialum in tall fescue results in alkaloids that depress livestock growth and reproduction (see Chapter 16 and Chapter 17) (Porter and Thompson, 1992). These compounds also can disrupt the population dynamics of small mammals that form an integral part of the natural grassland ecosystem. Prairie voles (M. ochrogaster) eating E+ tall fescue seed have exhibited reduced growth rates and reproductive success compared to voles eating uninfected seed (Durham and Tannenbaum, 1998).
Endophyte infection of tall fescue also can reduce small mammal survival and grazing preference. Conover (1998) found that meadow voles (M. pennsylvanicus) had higher mortality at high temperatures when fed E+ tall fescue vegetation. Pelton et al. (1991) reported a 21% reduction in the natural incidence of small mammals in E+ tall fescue compared to E- fields. Clay (2001) has postulated that changes in grazing patterns of prairie voles resulting from endophyte infestation may be responsible for botanical composition changes in tall fescue fields. Low endophyte infestation levels may result in voles selectively grazing tall fescue, which would allow other grass and forb species to invade pastures. High endophyte infestation reduces vole grazing and reproductive success, thereby diminishing their negative impact on tall fescue and contributing to tall fescue dominance. Giuliano et al. (1994) proposed that the decline in eastern cottontail rabbits in Kentucky may be due to the abundance of E+ tall fescue and its inhibition of rabbit reproduction.
There have been suggestions that avian species also may be affected negatively by endophyte infection of tall fescue. This is particularly true for seed-consuming birds. Captive zebra finches (Taeniopygia guttata) fed E+ tall fescue had higher mortality at ambient temperatures above 23°C than those fed E- seed. These birds also tended to develop an aversion to E+ tall fescue seed after a preconditioning period. Canada geese (Branta canadensis) grazing E+ tall fescue were found to lose body mass compared to geese grazing E- tall fescue. Geese that lost body mass on E+ tall fescue were able to regain body mass when put on a grain diet (Conover and Messmer, 1996a,b). Avian species also have exhibited negative reproductive effects in response to eating E+ tall fescue seed. Zavos et al. (1993) showed that Japanese quail (Coturnix japonica) fed E+ seed produced eggs with reduced fertility.
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