Dried distillers' grains with solubles (DDGS), a co-product of the fuel ethanol industry, has provided a source of supplement for livestock. This dissertation addressed the effects of DDGS supplementation with cattle grazing bermudagrass (Cynodon dactylon [L.] Pers.) pastures on performance, digestion, and digestive kinetics. The first objective of this study was to evaluate performance of stocker steers grazing 'Tifton 85' bermudagrass (TIF; Cynodon dactylon [L.] Pers. x C. nlemfu?nsis Vanderyst) when supplemented daily with varying rates of a DDGS supplement (SUPP; 0, 0.25, 0.5, or 1% BW). Steer ADG increased linearly (P < 0.01) as SUPP increased (0.61, 0.89, 0.96, and 1.10 kg/d for 0, 0.25, 0.5, and 1% BW SUPP). The second objective was to evaluate performance of steers grazing 'Coastal' bermudagrass (COS) with daily rates of SUPP (0, 0.25, or 1% BW). Steer ADG increased linearly (P < 0.01) as SUPP increased (0.67, 0.70, and 1.02 kg/d for 0, 0.25, and 1% BW SUPP). The third objective was to measure the effect of SUPP on subsequent feedlot and carcass traits. Compensatory gains likely occurred in the finishing phase for SUPP, resulting in decreasing feedlot ADG with increasing SUPP. The fourth objective of this study was to evaluate the effect of SUPP on in vitro gas production, digestibility, and methane production. Results indicated that DDGS may be supplemented to cattle to increase diet digestibility with a potential benefit of reduced methane production. This effect was greater for COS than for TIF. The final objective of this study was to evaluate the ruminal digestion kinetics of TIF as affected by month of year and SUPP. Forage of TIF from later months (August and October) have altered cell wall structural (increased cellulose and lignin) than early-season TIF (June). Increases in SUPP might have created an inhospitable rumen environment for fiber-degrading bacteria. Overall, supplementation of steers with DDGS may be an effective management strategy when bermudagrass forage mass was more abundant to allow for increased selective grazing. Supplementation with DDGS may result in increased diet digestibility and decreased methane production.