Two tall fescue forages, one containing a novel endophyte (HM4), and the other containing the Kentucky-31 wild-type endophyte (E+), were autumn stockpiled following late-summer clipping and fertilization with 56 kg N/ha. Beginning on 4 Dec 2003, sixteen 361 ± 56.4-kg dairy heifers were assigned to one of four 1.6-ha pastures (two each of HM4 and E+). Each pasture contained four 0.4-ha paddocks, one of which was assigned to each of four sampling dates (4 Dec, 26 Dec, 15 Jan, and 4 Feb). Each date represented the day that heifers entered that specific fresh paddock for the first time. Forage also was sampled from grazed paddocks on 26 Dec, 15 Jan, 4 Feb, and at termination (26 Feb). Fescue type x sampling date interactions did not affect total forage N, or partitioning of N within cell solubles (NDSN), or the cell wall (NDIN) for either pregrazed (P > 0.356) or postgrazed (P > 0.145) forages. Generally, fescue type had only minor effects on these N-related response variables. For pregrazed forages, N and NDSN declined in a strongly linear (P = 0.001) relationship with sampling dates. Concentrations of NDIN changed in erratic, and often higher-ordered relationships with time, but the magnitude of these responses generally was limited. Ruminal disappearance rate for pregrazed HM4 and E+ exhibited cubic (P = 0.013; range = 0.057 to 0.075/h) and quadratic (P = 0.004; range = 0.057 to 0.082/h) relationships with time, respectively. Disappearance rate for postgrazed HM4 and E+ forages only tended to be affected by sampling date (P > 0.060; mean = 0.065/h), or were unaffected (P > 0.169; mean = 0.066/h), respectively. Effective rumen degradability exhibited various curvilinear (P < 0.015) relationships with sampling dates; however, disappearance was extensive, and the overall range was relatively narrow (713 to 789 g/kg N).