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An experiment, with 39 barrows with high lean gain potential, was conducted to evaluate the growth responses of pigs fed a corn-soybean meal diet (CONTROL) and low-crude protein diets supplemented with crystalline lysine, threonine, tryptophan and methionine either on an ideal protein basis (IDEAL) or to a pattern similar to the control diet (AACON). In both cases the amino acid patterns were on a true ileal digestible basis. The initial and final body weights were 72.0 and 125.8 pounds. The diets were offered on an ad libitum basis or by feeding 80 percent of the ad libitum intake. Pigs were fed for 27 days. Three pigs were killed at the start of the experiment and three from each treatment were killed at the end to determine body chemical composition. Pigs fed the CONTROL diet grew faster and were more efficient than pigs fed the IDEAL and AACON diets. When feed intake was limited to 80 percent of ad libitum, weight gain decreased but efficiency tended to improve. The apparent fecal digestibility of protein was greatest in pigs fed the CONTROL diet and tended to be greater in pigs fed at 80 percent of ad libitum than those given ad libitum access to feed. Plasma urea concentrations were highest in pigs fed the CONTROL diet, regardless of feeding level. On a whole body basis, the protein concentration (g/kg) and the accretion rates of protein (g/d) were greater for pigs fed the CONTROL than for pigs fed the IDEAL and AACON diets. In summary, pigs fed the IDEAL and the AACON diets had lower growth performance, had less body protein and lower protein accretion rates than pigs fed the CONTROL diet. It remains unclear how to formulate low-crude protein amino acid-supplemented diets to ensure comparable growth performance and carcass characteristics to pigs fed corn-soybean meal diets.