Effects of the proportion of solubles in wet distillers grains plus solubles on in vitro fermentation and hydrogen sulfide production

Effects of substrates containing different proportions of distillers solubles (DS) to distillers grain (DG) on IVDMD, H2S production, gas production kinetics, VFA proportions, and culture fluid osmolality were evaluated in a randomized block design with a 2 × 3 + 1 factorial arrangement of treatments. Treatment substrates consisted of 15 or 30% DG with DS added within each DG concentration to yield proportions of DG:DS of 100:0, 75:25, and 50:50; the steam-flaked corn-based control treatment contained no DG. Two ruminally cannulated Jersey crossbred steers (BW = 590 kg) fed a 60% concentrate, steam-flaked corn-based diet were used as ruminal fluid donors. Duplicate cultures were incubated for 24 h to measure IVDMD and 48 h for gas production kinetics, with incubations replicated on separate days. No differences were observed among treatments for IVDMD (P > 0.15), but H2S production was increased (P < 0.01) by 39 and 73% for 15 and 30% DG, respectively, relative to the control. Moreover, H2S production increased linearly as the proportion of DS increased (P < 0.01). Osmolality was greater for the control (P < 0.001) than for other treatments, decreased (P < 0.001) with increasing DG concentration, increased linearly (P < 0.001) with increased DS in substrates, and increased over time (P < 0.001). Fractional rate of gas production (h-1) was less (P = 0.01) for 30 versus 15% DG, and lag time of gas production decreased as DS increased in substrates (linear, P = 0.02). Molar proportion of acetate was least (P = 0.02), propionate was greatest (P < 0.01), and acetate:propionate ratio was least (P = 0.02) for the control versus other treatments. In general, including DG in substrates and increasing proportions of DS increased H2S production, reflecting increased S concentrations. For both 15 and 30% DG, substrates with greater proportions of DS had increased total gas production and culture fluid osmolality.