PS3-8. Effects of Oxygenated Drinking Water on Feed and Water Intake, Gas Flux, Microbial Communities, Digestibility, and Ruminal Fermentation in Beef Steers and Cows on a Forage-based Diet.

Abstract Enteric methane (CH4) emissions from beef cattle contribute substantially to agricultural greenhouse gas production. Infusing oxygen in the anaerobic environment of the rumen could alter ruminal oxidation-reduction potential and potentially reduce methanogenesis. This study utilized nanobubble technology (Moleaer, Hawthorne, CA) to increase the dissolved oxygen (DO) concentration in drinking water and subsequently evaluated the effects of oxygen-enriched water (OEW) on feed and water intake, gas flux, microbial communities, digestibility, and ruminal fermentation in beef cattle fed a forage-based diet (76.6% wheat straw, 20.9% corn silage, 0.7% distillers grains, and 1.8% mineral supplement). Eight ruminally cannulated steers and eight mature cows were used in a crossover design consisting of two 35-d periods and randomly assigned to control water (CON; 3.6 mg/L DO) or OEW (16.1 mg/L DO). Two pens were utilized, located at the Colorado State University Climate Smart Research Facility, where each pen was equipped with five SmartFeed units and one GreenFeed unit (C-Lock Inc., Rapid City, SD) for measuring individual intake and gas emissions. One SmartFeed in each pen was dedicated to water to track consumption. Dry matter intake (DMI), water intake, apparent total tract digestibility, microbial community richness and diversity, ruminal fermentation parameters, and gas flux were measured. Data was analyzed using the MIXED procedure of SAS for all parameters except microbiome, which was analyzed using QIIME2 2024.10. The DO concentration of OEW was increased 4.5-fold compared to CON. In steers, DMI tended to increase (∼7%; P < 0.10), while water intake tended to decrease in both steers and cows (∼6-11%; P < 0.10). Steers receiving OEW reduced the apparent total tract digestibility of nutrients (P < 0.05). Methane, carbon dioxide, hydrogen, and oxygen flux were not affected by treatment (P > 0.10). Ruminal pH, DO, oxidation-reduction potential, total volatile fatty acid (VFA) concentrations, and VFA molar proportions were not affected when animals received OEW or control water (P > 0.10). Alpha and beta diversity of the rumen microbiome did not differ among steers consuming OEW and control water (P > 0.10). These findings indicate that moderate oxygen enrichment of drinking water did not alter ruminal fermentation conditions or gas flux, suggesting an inadequate dose or substantial resilience of the rumen microbiome to this mode of oxygen delivery. Reduced digestibility without methane mitigation suggests limited efficacy of OEW under the conditions evaluated. Future research should examine methane emissions relative to time since water intake to determine whether transient post-drinking effects occur.