Two tall fescue (Festuca arundinacea Schreb.) forages, one containing a novel endophyte that produces low or nil concentrations of ergot alkaloids (HiMag-4), and the other containing the wild-type endophyte (E+), were autumn-stockpiled, following late-summer clipping and fertilization with N. Beginning on 4 Dec. 2003, sixteen 361 ± 56.4-kg replacement dairy heifers were stratified by weight and breeding and assigned to one of four 1.6-ha pastures (two each of HiMag-4 and E+). Pastures were sampled before grazing was initiated (4 Dec.), each time heifers were allowed access to a new paddock (26 Dec., 15 Jan., and 4 Feb.), and when the study was terminated (26 Feb.). For concentrations of fiber components, there were no interactions (P > 0.064) between fescue type and sampling date for either U or G forages. Over sampling dates, concentrations of NDF (565 to 678 g/kg), ADF (277 to 349 g/kg), hemicellulose (288 to 340 g/kg), cellulose (250 to 281 g/kg), and lignin (36.1 to 100.5 g/kg) varied (P < 0.053) with sampling date, but patterns were almost exclusively curvilinear with time. For ruminal disappearance kinetics of DM, disappearance rate was not affected (P > 0.186) by any treatment factor (overall mean for both U and G = 0.050/h); similar responses were observed NDF disappearance (overall mean for both U and G = 0.048/h). Interactions of fescue type and sampling date were observed in U (P = 0.006) and G (P = 0.012) forages for effective ruminal disappearance of DM; however, estimates were relatively high for all forages (overall range = 595 to 700 g/kg). Similarly, effective disappearance of NDF was also relatively high for all forages (overall range = 513 to 584 g/kg of NDF).