Date of Award
Master of Science
Stephanie L. Hansen
Commonly, protein and energy sources in feedlot cattle diets in the United States are co-products of the ethanol industry, such as dried distillers grains plus solubles. However, the inclusion of co-products is limited by the high sulfur content from the use of sulfuric acid in the ethanol production process. High sulfur diets have been shown to decrease cattle growth performance and may lead to sulfur toxicity. Dietary sulfate is reduced to sulfide or hydrogen sulfide by ruminal sulfate reducing bacteria. This process is pH dependent, thus increasing ruminal pH is thought to decrease hydrogen sulfide production. Previous research has shown the risk for sulfur toxicity may be decreased by increasing roughage inclusion in feedlot diets to greater than 6 to 8% of DM; however, little information is available comparing roughage sources or dietary concentrations to decrease the risk of toxicity while maintaining cattle performance. Thus, the succeeding research trials were designed to compare the impacts of two roughage sources on ruminal pH and ruminal hydrogen sulfide concentrations and to determine the effect of increasing roughage concentration on ruminal pH, ruminal hydrogen sulfide, cattle intake, and feedlot cattle growth performance. The results of the research show the source of roughage, when balanced on an equal neutral detergent fiber basis, did not differ in the ability to positively affect ruminal pH, hydrogen sulfide, or cattle intake. When evaluating the second research objective, increasing dietary roughage increased dry matter intake and decreased the rate of intake. Even though dry matter intake increased, the addition of roughage up to 17.3% of DM did not affect average daily gain or feed efficiency. This suggests there may be synergy between roughage and fibrous dried distillers grains, which allowed for greater cellulose digestion and compensated for the energy dilution of the diets. Ruminal pH also increased with the increased dietary roughage, suggesting the increased number of smaller meals positively influenced ruminal pH. In the first study, ruminal pH was measured via an indwelling bolus and increasing roughage resulted in a decrease in time spent under pH 5.4, 5.6, and 5.8. A lesser amount of time spent at decreased pH values is beneficial in decreasing the proportion of hydrogen sulfide in the rumen. Furthermore, hydrogen sulfide concentrations decreased with the increased inclusion of dietary roughage. The outcomes of both experiments suggest a strong negative correlation between ruminal pH and hydrogen sulfide, where, as ruminal pH increased, hydrogen sulfide decreased. In the first study a breakpoint at a pH of 5.6 was observed, where above 5.6, ruminal pH was no longer strongly influencing hydrogen sulfide concentrations; however, these differences may be attributed to differing experimental design in these studies. The results of both studies suggest including 7 to 8% neutral detergent fiber of either roughage source in high S feedlot cattle diets will increase ruminal pH and decrease hydrogen sulfide concentrations, thus decreasing the potential for sulfur toxicity. Further research is necessary to uncover if there are additional influences of increased roughage on ruminal hydrogen sulfide concentrations beyond ruminal pH alone.
Morine, Sara, "Determining the optimal dietary roughage source and inclusion to decrease hydrogen sulfide in steers fed high-sulfur finishing diets" (2014). Graduate Theses and Dissertations. 13703.