Conventional diets containing corn and soybean meal fed to growing pigs can be reduced in protein by replacing a portion of the protein with crystalline amino acids. Crystalline amino acids are of synthetic origin but are exactly the same as those found in naturally occurring proteins. Crystalline amino acids are manufactured by bacteria through fermentation processes. When used in diets, crystalline amino acids are digested 100%, thus decreasing overall nitrogen excretion and in turn reducing ammonia emission into the air. Previous studies have shown that the level of inclusion of these amino acids is limited to diets with minimal decrease in dietary crude proteins, such as 2 to 3%. Decreasing above this level, i.e., 3.6%, have been shown to cause reduction in whole body protein growth, and intestinal tissue growth. However, the current study shows that reducing crude protein to 3.3% is warranted (compared to 2.4% as previously reported by our laboratory) as it does not impact intestinal protein synthesis and thus intestinal protein growth, an important factor in maintaining overall animal health and well-being. At this level of crude protein reduction, ammonia emission may be reduced by more than half compared to that from pigs fed conventional diets.