73 The effect of feed sulfur and water sulfate on ruminal hydrogen sulfide concentrations and gastrointestinal tract permeability in beef heifers.

Abstract Consumption of high-sulfate water and high-sulfur feed by cattle results in the production of ruminal hydrogen sulfide gas (H2S) which is a known risk factor for the development of sulfur-induced polioencephalomalacia in ruminants. However, it is unclear whether water sulfate or feed sulfur contribute more to elevation of ruminal H2S gas concentrations. This study evaluated the effect of feed sulfur and water sulfate on feed and water intake, ruminal H2S gas concentration, ruminal fermentation, and permeability of the gastrointestinal tract. Eight ruminally cannulated Simmental-cross heifers (body weight 531 ± 38.1 kg) were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial treatment arrangement. Main factors included low (LW; 2689 ± 98.0 mg/L) or high (HW; 3653 ± 165.2 mg/L) water sulfate and diets formulated to contain low (LF; 0.3% S) or high (HF; 0.4% S on a DM basis) sulfur. Dietary sulfur was manipulated using equal quantities of dried distiller’s grain with differing S contents. Dry matter intake, water intake, reticulo-ruminal pool size, ruminal pH and short-chain fatty acid (SCFA) concentrations, and H2S gas concentrations were evaluated. Additionally, total-tract and post-ruminal gastrointestinal permeability were assessed. Data were analysed using the mixed procedure of SAS with fixed effects of period, water sulfate, feed sulfur, and the feed × water interaction, with random effects of heifer and period by square, and ruminal pH and SCFA were analyzed including time as a repeated measure. Dry matter intake and water intake were not affected by water sulfate, feed sulfur, or their interaction (P≥0.23). Mean ruminal H2S gas concentration and area under the curve were greater for HF (P< 0.01) than LF, and greater for HW (P≤0.02) than LW. The area under the curve for ruminal H2S gas tended to be less (feed × water, P=0.08) for LFLW than all other treatments. Ruminal pH tended to be less (P≤0.08) for LF than HF, and the total SCFA concentration was greater (P≤0.02) for LF than HF. There was no effect of water sulfate on ruminal pH or total SCFA concentration. Feeding LF reduced (P< 0.01) the molar proportion of acetate and increased (P< 0.01) the molar proportion of propionate relative to HF. Total reticulo-ruminal digesta weight was not different (P≥0.43) but ruminal DM concentration was greater (P=0.05) for LF than HF. Total-tract (P≥0.12) and post-ruminal (P≥0.18) permeability were not affected. While neither water sulfate or feed sulfur reduced feed or water intake, or altered gastrointestinal permeability, high sulfur in feed and high sulfate in water independently increased ruminal H2S concentration.