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

Abstract

<h2>ABSTRACT</h2> 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.