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Pasture alone does not always provide adequate nutrients for growing lambs because of variations in forage quality and availability. Supplementation of grazing lambs is one option to address this limitation, and this study evaluated the effect of soy hull (SH; 13.9% CP; 48.7% ADF; 54% TDN) and corn gluten feed (CGF; 17.9% CP; 17.0% ADF; 76% TDN) supplementation on performance of hair sheep and wool × hair sheep lambs during spring grazing. Thirty-six, 7.5-mo old purebred hair (Barbados Blackbelly and St. Croix) and crossbred wool (Dorset) × hair sheep lambs rotationally grazed predominantly Jesup tall fescue with Max-Q endophyte pasture (9.0 to 16.7% CP; 41.2 to 58.5% ADF; 46 to 59% TDN) from late March to early June. Lambs were randomly assigned to a pasture-only, and a SH or CGF supplemented group balanced by breed type. Lambs grazed as a single group and were moved to a new pasture strip at 3 to 6 d intervals based on visual appraisal of forage availability. Supplement was provided daily at 2% of BW (DM basis) at individual Calan feeding stations. Carcass traits were evaluated after slaughtering with standard procedures at the end of the 77 d grazing period. All data were analyzed as a completely randomized design with a 2 × 3 factorial treatment arrangement: breed type (pure- or cross-bred) with or without supplementation (SH and CGF or pasture-only). Hot carcass weight (HCW) was greater (P< 0.001) in crossbred than purebred lambs, but dressing percentage was not affected by breed type. Furthermore, HCW (17.5 or 17.6 vs. 13.3 kg) and dressing percentage (45.2 or 44.1 vs. 41.1%) were greater (P< 0.01) in supplemented (SH or CGF) vs. pasture-only lambs, respectively. Muscle pH after 24-h post-mortem was not influenced (P= 0.39) by breed type or supplementation. Loin eye area was greater (15.6 vs. 13.0 cm2; P< 0.05) in crossbred than purebred lambs. All cuts from fore- and hind-saddles were greater (P< 0.01) in crossbred than purebred lambs, except neck cuts, and also greater (P< 0.01) in supplemented than pasture-only lambs. Results indicated that supplementation and crossbreeding had significant effects on carcass quality.