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Five experiments, using 216 barrows and gilts (initial weight 19.9 to 23.7 kg), were conducted to evaluate the effects of improving amino acid balance by supplementing low-protein corn-soybean meal diets with essential amino acids. Three experiments were growth studies lasting approximately 3 wk, and the other two were 4-d metabolism trials. The control diets in each of the experiments were formulated to contain .80% lysine and contained approximately 17% CP. The other diets were formulated from a basal diet containing a 10.9% CP, fortified corn-soybean meal mixture, which included crystalline L-lysine.HCI, L-tryptophan, L-threonine, L-isoleucine, DL-methionine and L-valine to correct amino acid deficiencies. Nonessential N (glutamic acid or urea) also was added to some of the diets to increase the CP equivalent to 12 or 13%. Supplemental K (as a salt of bicarbonate or glutamate) was included in selected diets to increase the K concentration to the same level as that of the control diet. Growth rate of pigs fed the basal diet was similar (P greater than .05) to that of the control diets in only one growth study. Added glutamic acid and urea did not improve either growth rate or N retention. Added K improved K digestibility but did not increase K retention, N retention or growth rate. Improving amino acid balance by adding essential amino acids to low-protein diets did not benefit performance beyond that of a typical corn-soybean meal diet. Under our conditions, K, N, and nonessential N were not limiting.

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