THE EFFECT OF REDUCING EXCESS DIETARY AMINO-ACIDS ON GROWING-FINISHING PIG PERFORMANCE - AN EVALUATION OF THE IDEAL PROTEIN CONCEPT

Seventy-two gilts were used to determine the effect of reducing excess amino acid intake on growing-finishing pig performance. Separate diet s were formulated for the growing (20 to 55 kg BW) and finishing (55 t o 100 kg BW) periods. For each period, three diets were formulated tha t varied in total crude protein level and contained similar levels of digestible ideal protein. Crystalline amino acids were added to the lo w protein diets to overcome potential deficiencies. The grower diets c ontained .66% apparent ileal digestible lysine and contained 16.6, 15. 0, and 13.0% CP, respectively; for the finisher diets, these values we re .55% digestible lysine and 14.2, 12.8, and 11.0% CP, respectively. Amino acid analyses and a separate digestibility trial were conducted to confirm digestible amino acid levels in the dietary ingredients. Du ring the growing and the overall growing-finishing period, daily gain, feed intake, and gain:feed were not affected (P > .10) by dietary tre atment. Daily gain tended to be lower (P = .06) and gain:feed was poor er (P < .05) for pigs fed the 11.0% CP diet during the finishing phase . Although backfat thickness tended to be greater (P = .07) for pigs f ed the lower-CP diet, estimated carcass lean yield was not affected (P > .10) by dietary treatment. Results of this study show that dietary CP can be reduced to 13% in the growing and 12.8% in the finishing die ts of pigs as long as crystalline amino acids are added to match the a pparent ileal digestible amino acid ratios in an assumed ideal protein .