Sulphur (S) dietary excess can limit productive performance and increase polioencephalomalacia (PEM) incidence in feedlot cattle (FC). Sulphur excess ingested is transformed to hydrogen sulphide (H2 S) by sulfo-reducing ruminal bacteria (SRB), being high ruminal H2 S concentration responsible for aforementioned damages. As the ruminal mechanisms involved in H2 S concentrations increase have not been elucidated, this study aimed to evaluate the ruminal environment, and the association between ruminal H2 S and dissimilatory SRB (DSRB) concentration in FC experimentally subjected to S dietary excess. Twelve crossbred steers were randomly assigned to one of two dietary S levels (6 animals per treatment): low (LS, 0.19% S) and high (HS, 0.39% S obtained by sodium sulfate inclusion at 0.86%). The study lasted 38 days, and on days 0, 22 and 38, ruminal gas samples were taken to quantify H2 S concentration, and ruminal fluid to determine total bacteria, DSRB, protozoa, volatile fatty acid and ammonia nitrogen concentration. For ruminal H2 S concentration, S dietary × sampling day interaction was significant (p < 0.001), so that the greater concentration was observed on days 22 and 38 with the HS diet. The remaining ruminal parameters were not affected by dietary S level, and no significant correlation between H2 S and DSRB concentrations was observed. The ruminal adaptation that maximizes H2 S production in FC consuming S excess does not seem to be associated with biological or biochemical alterations, nor DSRB concentration changes. The microbial diversity and ruminal environment were resilient to the S excess evaluated, suggesting that 0.39% of dietary S achieved by 0.86% sodium sulfate addition, could be used without disturbances on digestion nor health of FC.
Keywords: feedlot cattle; ruminal hydrogen sulphide; sulfo-reducing bacteria.
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