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Evaluating impact of animal agriculture on air quality has been the focus of recent research. Ammonia (NH) volatilization occurs when undigested protein in feces and urea in urine is broken down by bacteria and enzymes. Information regarding NH emission from equine facilities is limited, and effects of CP intake on NH emissions have not been investigated. Nine mature geldings were used in a 3 × 3 replicated Latin square design study to determine effects of dietary CP on potential NH losses from feces and urine. We hypothesized feeding horses above the CP requirement would result in an increase in NH emissions from urine and feces and different bedding materials would affect NH emissions from urine. Diets were formulated using different ratios of bahiagrass () and Tifton-85 bermudagrass () hays, and a commercial vitamin mineral supplement to provide 3 different CP concentrations and labeled in relation to each other: LOW-CP, MED-CP, and HIGH-CP (10.6%, 11.5%, and 12%, respectively). Each study period consisted of an 11-d diet adaptation phase, followed by a 3-d total collection of urine and feces. To determine total nitrogen (TN) and urea-N concentrations, samples were pooled by period ( = 9). For in vitro determination of NH concentrations, urine and fecal samples were pooled within period by diet ( = 3) and mixed with either wheat straw or wood shavings. Ammonia emission of these samples was measured using a vessel system with an airflow rate (2.5 L/min) at 20°C over a 7-d period. Concentration of NH in each vessel was measured using a photoacoustic multigas analyzer. Temperature, airflow rate, and NH concentration in each vessel were used to calculate NH emission rate (ER). Data were analyzed using a mixed model ANOVA with repeated measures. Urinary TN and urea-N excretion increased as CP intake increased ( < 0.0001). Vessel urinary NH concentrations were not different across diets ( = 0.1225), ranging from 55.48 ppm (LOW-CP) to 101.14 ppm (HIGH-CP); however, they differed between bedding types ( < 0.0001), with straw higher than shavings (97 vs. 73.5 ppm, respectively). Cumulative urinary NH ER tended to be different across diets ( = 0.0550) ranging from 5.87 g/m to 9.97 g/m and bedding types ( = 0.0129), with straw being higher than shavings (11.1 vs. 6.9 g/m, respectively). Overfeeding CP to horses can lead to increased urinary TN and urea-N excretion, which could lead to greater of NH in the atmosphere.