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The effect of dietary manipulation on odor emission in a research pig facility was evaluated with 26 finishing gilts (initial weight 161 lb). The two diets were formulated to contain 13% crude protein or 9% crude protein supplemented with crystalline amino acids. Two environmental chambers were used and each housed a group of four or five gilts for 21 days. Relative humidity, temperature and air exchange were maintained throughout the experiment. Samples of feces and air were taken on days 4, 7, 11, 14, 18 and 21 of the experiment. Aerial ammonia and hydrogen sulphide concentrations were measured using detector tubes. Air samples were collected in 25 L Tedlar bags and analyzed within 24 hours, by an olfactometer and a trained panel at Iowa State University. Hydrogen sulphide concentration was < .25 ppm for both treatments. Ammonia concentration was significantly higher when the 13% crude protein diet was provided (P < .01). Odor levels measured by the olfactometer were not different between treatments. These results suggest one method by which the odors produced by swine units can be decreased to potentially benefit both animal and human health.