Effects of dietary roughage and sulfur in diets containing corn dried distillers grains with solubles on hydrogen sulfide production and fermentation by rumen microbes in vitro

Dried distillers grains with solubles (DDGS) have been used in production animal diets; however, overuse of DDGS can cause toxic concentrations of ruminal hydrogen sulfide gas (H₂S), resulting in polioencephalomalacia, a deleterious brain disease. Because H₂S gas requires an acidic rumen environment and diet can influence ruminal pH, it has been postulated that dietary manipulation could help mitigate H₂S production. The objective of this study was to assess the effect of dietary roughage and sulfur concentrations on H₂S production and rumen fermentation. In Exp. 1, 7 dual-flow continuous culture fermenters were used in 4 consecutive 9-d periods consisting of 6 d of adaptation followed by 3 d of sampling. At the conclusion of each 9-d continuous culture period, adapted rumen fluid was used for inoculation of 24-h batch culture incubations for Exp. 2. For both experiments, 6 dietary treatments were formulated to consist of 0.3%, 0.4%, or 0.5% dietary sulfur (LS, MS, and HS, respectively) and 3% or 9% dietary roughage (LR and MR, respectively), using grass hay as the roughage source. A corn-based diet without DDGS was used as a control diet. Headspace gas was sampled to determine H₂S production and concentration. In Exp. 1, greater dietary roughage had no effect (P = 0.14) on H₂S production but did create a less acidic environment because of an increase (P < 0.01) in the in vitro pH. In Exp. 2, an increase in dietary sulfur caused an increase (P = 0.04) in ruminal H₂S production, but there was no direct effect (P = 0.25) of dietary roughage on H₂S production. Greater dietary roughage resulted in a less (P = 0.01) acidic final batch culture pH but a lower (P < 0.01) total VFA concentration. Further investigation is needed to determine a more effective way to mitigate ruminal H₂S production using dietary manipulation, which could include greater inclusion of dietary roughage or the use of different roughage sources.