Increased Length of Gestation

Gestation length of mares increased 27 d when consuming E+ fescue compared with mares consuming E- fescue (Monroe et al., 1988). Putnam et al. (1991), Earle et al. (1990), and Redmond et al. (1994) observed similar results. Severe dystocia is frequently observed in mares that try to foal after an extended gestation period. Supplementing E- and E+ mares on pastures with 50% of their National Research Council (NRC) requirements for energy, using whole shelled corn (Zea mays L.), provided no beneficial effects on length of gestation or dystocia. In the Earle et al. (1990) study, 66% of the mares grazing E+ with energy supplementation exhibited prolonged length of gestation and died from dystocia, whereas the same signs and effects were noted for 50% of the mares grazing E+ without supplementation. Putnam et al. (1991) reported 10 of 11 mares grazing E+ fescue experienced obvious clinical dystocia, and four of them died during parturition, with only one foal surviving the natal period.

The dystocia appears to be a result of inadequate preparation of the reproductive tract for foaling, prolonged gestation, and fetal malpresentation. Prolonged gestation usually causes foals to have larger than normal skeletal frames, thereby increasing the difficulty of expelling the fetus through an unprepared tract (Monroe et al., 1988; Putnam et al., 1991; Redmond et al., 1991). Additionally, foals are often rotated 90 to 180° from the normal position for delivery (Taylor et al., 1985; Monroe et al., 1988; Redmond et al., 1994). The failure of events that initiate preparation for and cause normal parturition results in the subsequent catastrophic events of dystocia, as well as, in some instances, mare and foal mortality when mares graze E+ fescue.



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