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Nitrogen losses from cattle feedlots are a concern due to loss of valuable N and enrichment of the atmospheric N pool. Nutritional methods to decrease losses would have economic and environmental benefit. One method to decrease N losses is by increasing carbon on the pen surface. From a management perspective, feeding a diet that will increase carbon may be the most cost effective. Therefore, three experiments evaluated feeding corn bran (less digestible than corn) at either 0, 15, or 30% of the diet. The 15 and 30% bran diets increase organic matter (carbon) excretion by approximately 0.5 and 1.0 kg/steer/d, respectively. Compared with no bran, feeding 15 and 30% decreased feed efficiency by 7.8 and 10.4%, respectively. Nutrient balance was assessed for two trials from October through May and one trial from June to September. During the trials from October to May, N losses were decreased by 14.5 and 20.7% for the 15 and 30% bran diets compared with no bran. Feeding 15 or 30% bran did not influence N losses in the experiment from June to September. Increasing the carbon: nitrogen ratio of manure prior to cleaning open-dirt feedlots has variable results depending on time of year.