For many years, veterinarians and horse owners reported reproductive problems in mares that consumed tall fescue (Garrett et al., 1980; Villahoz et al., 1984; Poppenga et al., 1984). Monroe et al. (1988) determined that the endophyte of tall fescue is the causative agent for reproductive abnormalities in gravid mares (Fig. 17-1). They reported that increased gestation lengths, agalactia, foal and mare mortality, tough and thickened placentas, weak and dysmature (large-framed emaciated-looking) foals, and reduced serum prolactin and progestagen levels occurred in mares consuming E+ pasture, whereas gravid mares on endophyte free (E-) pasture appeared normal.
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Fig. 17-1. Comparison of the effects of E+ and E- tall fescues on gestation length, foal mortality, agalactia, incidence of placental retention, and rebreeding response in mares (adapted from Monroe et al., 1988). Stars indicate significant difference between treatments (P < 0.05).
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