ABSTRACT: Ninety crossbred beef calves (277.7 ± 7.1 kg) were utilized in a completely randomized design to determine supplement and rumen undegraded protein (RUP) influence on calf performance while grazing stockpiled tall fescue. Calves were supplemented at 1.15% of BW DM with dried distillers grains w/solubles (DDGS); 80.7% DDGS, 19.3% AminoPlus (DDG19); 80.7% soybean hulls (SBH), 19.3% AminoPlus (SBH19); 61.7% SBH, 38.3% AminoPlus (SBH38), or unsupplemented control (CON). We hypothesized supplement would increase ADG, and supplements with increased RUP would improve performance. Calves were stratified by BW, source, color, and sex, and then randomly assigned to a pasture. Pasture replicates (n = 15) were fertilized with nitrogen at 24.4 kg/ha on 25 August 2014 and at experiment initiation were blocked by percent endophyte infection. Weekly forage allocations were based on 3.25% BW DM hd⁻¹d⁻¹. Supplement and forage DM allocations were adjusted every 21 d using interim BW. Forage DM substitution was set at 0.5 times average supplemental DMI. Forage allocations were adjusted to maintain 509 kg DM/ha residual. Proc Glimmix procedure of SAS was used for ANOVA. Supplement increased (P < 0.01) ADG and final BW compared with CON (0.68 vs. −0.03 kg/d; 336.0 vs. 276.7 kg). ADG did not differ (P > 0.05) between DDG19 and SBH38 (0.78 vs. 0.73 kg/d), however DDG19 increased (P < 0.05) ADG compared with SBH19 (0.62 kg/d) and DDGS (0.59 kg/d). ADG was not different (P > 0.05) between SBH38, SBH19, and DDGS. Forage DM disappearance was not different (P > 0.05) between CON (6.7 kg/d), DDG19 (6.5 kg/d) and SBH38 (6.2 kg/d). SBH19 (5.5 kg/d) forage DM disappearance did not differ (P > 0.05) from DDG19, SBH38 whereas DDGS (4.3 kg/d) decreased (P < 0.01) forage DM disappearance compared with CON, DDG19, and SBH38. DDG19 improved (P < 0.05) supplemental G:F compared with DDGS, (0.23 vs. 0.18 kg/kg). SBH38 (0.22 kg/kg) and SBH19 (0.19 kg/kg) supplemental G:F did not differ (P > 0.05) compared with DDG19 or DDGS. DMI did not differ (P > 0.05) between DDG19 (10.0 kg/d), SBH38 (9.7 kg/d), and SBH19 (8.9 kg/d), and was least for DDGS (7.8 kg/d). Supplementation increased ADG, while additional RUP improved ADG and supplemental G:F.