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Abstract. Emissions of carbon dioxide, methane, and nitrous oxide – potent greenhouse gases - from stored beef feedlot manure are a significant concern relative to climate change. Research on methane reduction strategies for enteric emissions has identified the application of organic additives, such as bromoform and linseed oil, to ruminant diets as potential solutions for reducing enteric emissions and pathogenic bacteria in excreted manure. The objective of this study was to determine the effect of bromoform and linseed oil on greenhouse gas emissions from beef feedlot manure, and on E. coli concentration in beef cattle manure, during a 5-week storage period. The experiment used a completely randomized block design (CRBD) with 4 replications of 5 treatments: 5.5 g/kg and 11 g/kg of linseed oil, 4.3 g/kg, and 8.6 g/kg of bromoform, and a control receiving no additives. Treatments were added to a 3-liter mix of 50% manure, 50% soil, mixed by hand, and stored in airtight columns (10-cm diameter x 40-cm tall) in a greenhouse maintained at 25 C during the storage period. Gas samples were collected 10 times during the 5-week test period using a 15 ml syringe and were analyzed using gas chromatography to determine concentrations of methane, carbon dioxide and nitrous oxide. A 1-cm diameter core of material was removed from the top 20 cm of each column 4 times during the sampling period to conduct bacterial enumerations. Quantification of E.coli in samples was determined by incubating serial dilutions for 24 hours at 36 C and manually counting colonies. Preliminary results of the study showed that through 5 weeks of observation, 11g/kg linseed oil reduced the average concentration of E. coli (p <0.05) compared to all other treatments. Preliminary results also indicate that bromoform at 8.6g/kg decreased carbon dioxide emissions but neither bromoform concentration had any significant effect on methane or nitrous oxide emissions compared to control. Linseed oil at 11g/kg increased methane emissions compared to control but neither linseed oil concentrations significantly impacted the average flux of carbon dioxide, or nitrous oxide from manure storages when compared to control.