Fall-grown oat has shown promise as an emergency fall forage option, or to extend the grazing season in Wisconsin. Our objectives for this project were: (1) to assess the pasture productivity and forage characteristics of 2 fall-grown oat cultivars (Ogle and ForagePlus; OG and FP, respectively) using grazing initiation dates timed to late-September (EARLY) or mid-October (LATE); and (2) to evaluate growth performance by heifers grazing these oat forages compared with performance of heifers reared under controlled conditions with traditional confinement management (CONTROL). A total of 160 gravid Holstein heifers (80 heifers/yr) were stratified by weight, and assigned to 10 research groups (8 heifers/group). Initial BW was 509 ± 40.5 kg in 2013 and 517 ± 30.2 kg in 2014. Heifer-groups were maintained as units, and assigned to specific pastures arranged as a 2 × 2 factorial of oat cultivars and grazing initiation dates. Grazing heifer groups were allowed to strip-graze oat pastures for 6 h daily before returning to the barn, where they were offered a forage-based basal TMR. During both years, oat forage mass increased until early-November before declining in response to freezing weather conditions, exhibiting linear (P < 0.01) and quadratic (P < 0.01) effects of calendar date, regardless of oat cultivar. For 2013 and 2014, the respective maximum forage mass was 5329 and 4501 kg/ha for FP, and 5046 and 5111 kg/ha for OG. ForagePlus oat did not reach the boot stage of growth during either year; in contrast, OG matured more rapidly, and reached a late-heading stage during 2013, but only the early-boot stage in 2014. For 2013, ADG for CONTROL did not differ from grazing heifer groups (overall mean = 0.63 kg/d; P = 0.619); however, ADG from FP was greater than OG (0.68 vs. 0.57 kg/d; P = 0.02), and greater from EARLY than LATE (0.82 vs. 0.43 kg/d; P < 0.01). During 2014, ADG from CONTROL exceeded grazing heifer groups (0.81 vs. 0.57 kg/d; P = 0.01), and ADG from EARLY again exceeded LATE (0.70 vs. 0.44 kg/d; P < 0.01). These results suggest that delaying grazing until mid-October to allow more oat forage to accumulate will consistently suppress heifer growth performance.