Effects of Distillers Grains and Substrate Steam-Flaked Corn Concentration on In Vitro Dry Matter Disappearance, Gas Production Kinetics, and Hydrogen Sulfide Production¹

Effects of 3 levels of distillers grains (DG) and 3 ratios of steam-flaked corn (SFC) to ground corn (GC) were used to evaluate IVDMD, in vitro gas production kinetics, and in vitro H2S production using ruminal fluid from 2 Jersey crossbred steers. Substrates included either corn (CDG) or sorghum distillers grains (SDG). Within each type of DG, treatments were 0, 15, or 30% DG (DM basis) and ratios of SFC:GC of 50:50, 75:25, or 100:0. With CDG, IVDMD tended (P = 0.06) to increase linearly as SFC increased in substrates, and increasing CDG increased H2S production (linear, P<0.01). Fractional rate of gas production tended to decrease quadratically (P = 0.07) with decreased SFC in substrates. Molar proportion of propionate (P = 0.05) and acetate:propionate ratio (A:P; P = 0.03) responded quadratically to CDG level, with the greatest values at 15% DG. With SDG, IVDMD decreased (P = 0.02) as the percentage of SFC decreased and tended (P = 0.09) to increase as SDG level increased. Similar to CDG, H2S production increased linearly (P = 0.02) as SDG increased from 0 to 30% of the DM. Fractional rate of gas production was greatest (quadratic, P = 0.04) for 75:25 ratios of SFC to GC and was not affected by SDG level (P > 0.23). Total VFA concentration decreased (P = 0.03) as proportion of SFC decreased, and increasing SDG tended to decrease propionate (P = 0.09) and increase A:P (P = 0.06). Overall, increasing concentration of CDG or SDG increased in vitro H2S production. Effects of DG concentration were largely independent of the percentage of SFC in the substrate for IVDMD and gas production kinetics, but adding DG tended to increase A:P proportions in vitro.