Three commercial swine farms with side-by-side 1100- head finishing units were fed two diets with varying protein levels. Odor threshold, ammonia and hydrogen sulfide were collected from the pit fans. The high protein (HP) treatment averaged 1420 odor units compared to 1035 odor units for the low protein (LP) treatment, reducing odor by 27% (P= 0.02). Reduction in H2S concentration was not significant, averaging 0.92 ppm and 0.59 ppm for the HP and LP treatments, respectively (P = 0.09). Concentrations of NH3 were 12.3 ppm and 9.1 ppm for the HP and LP treatments, respectively (P =0.10). Seasonal differences in H2S (P= 0.002) and NH3 (P=0.05) were indicated but the cause of this difference was not diet related and could be due to a number of seasonally-related operation attributes. This study demonstrates that dietary manipulation by addition of synthetic amino acids replacing soybean meal is a method pork producers can use to decrease the odor intensity of their pork production site.
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