UC Davis

Urgency to reduce anthropogenic sources of greenhouse gases (GHG) has substantially increased in recent years. Livestock, particularly cattle, represent a large majority of methane (CH4) generated in agriculture due to their digestive anatomy as a ruminant and their widespread presence supporting human populations worldwide. Careful manipulation of rumen fermentation and other related pathways to synthesize less CH4 could be achieved through the supplementation of feed additives with unique non-nutritional profiles. The first chapter of this dissertation outlines feed additives that either inhibit methanogenesis directly or have rumen modifying capacity to potentially produce less CH4 with a focus on in vivo models. The subsequent three chapters investigate implementing distinct additives into diets of beef or dairy cattle and their ability to suppress CH4 production along with potential impacts on performance. Various plant species are of interest as anti-methanogenic feed additives because of their phytochemical profile and ubiquity in nature. The second chapter of this dissertation evaluated lemongrass, a plant often characterized as rich in phytochemical substances, as a potential anti-methanogenic feed additive in growing beef steers. A random complete block design was organized with 20 beef steers half of which were assigned to a control diet with 0% lemongrass (CON) and the remaining 10 receiving a diet with lemongrass included at a rate of 2% of DMI (LGT). Gas production (CH4, CO2, and H2) was measured over 15 weeks. Analyses revealed that steers in the LGT versus CON group produced 9.9% more CH4 (P < 0.05) overall likely due to the displacement of high energy feed with a highly fibrous additive. Both treatment groups were similar regarding DMI, ADG, and total gain over the experiment (P > 0.05). I conclude that low concentrations of condensed tannins were responsible and no improvements in performance. The third chapter of this dissertation compared effectiveness of monensin, an ionophore, and RumenProof, a peroxidase antimicrobial, on animal performance including CH4 emissions, digestibility characteristics, blood metabolites, milk yield (MY), energy corrected milk (ECM), milk composition, and feed conversion (FCE) efficiency using a 3 x 3 Latin Square Design. Eighteen Holstein lactating dairy cattle in early to mid-lactation were blocked by milk production and parity. Dairy cows were similar across treatments for CH4 production, yield (CH4 g/kg DMI), and intensity (CH4 g/kg ECM) (P > 0.05). Milk production of cows was not affected by treatments, but milk urea nitrogen and solids non-fat tended to decrease in both monensin and RumenProof groups compared to control (P < 0.10). Digestibility of protein, starch, and NDF were unaffected by either treatment (P > 0.05). The lack of reduction in emissions with supplementation of monensin aligns with inconsistent results in the literature. Antimicrobials have previously demonstrated effects on ruminant digestibility; however, dietary conditions, length of adaptation, and dose levels are subject to cause variability in results. The fourth and final chapter of this dissertation explored the effectiveness of Amplio, a Bacillus subtilis direct fed microbial, on CH4 production and performance in lactating dairy cattle. Eighteen multiparous Holstein cows early to mid-lactation were blocked by DIM and balanced by MY and randomly assigned to a treatment of either 0 colony forming units (CO; CFU), 10 billion CFU (LD), or 30 billion CFU (HD) of B. subtilis in a 3 x 3 Latin Square Design. Animal performance, including DMI, MY, ECM and FCE were assessed, and no differences (P > 0.05) were detected due to treatment. Production of CH4 was 443, 426, and 425 (g/d) in the CO, LD, and HD group, respectively (P > 0.05). Other gases including CO2 and H2 remained unaffected by treatment inclusion of either dose of Amplio in addition to CH4 yield (g/kg DMI) and CH4 intensity (g/kg ECM). This experiment demonstrated that at these two dosages of Amplio versus CO neither animal performance nor enteric CH4 emissions were different. Lack of effects due to inclusion of B. subtilis is likely due to either lacking the ability to impact methanogenesis, carryover effects of the study design, or be a combination of a suboptimal dose and the once per day offering. Further experiments with greater levels of the probiotic and consistent treatment consumption by the animal may show better effectiveness in reducing CH4 emissions.