Limiting order of amino acids in a low-protein corn-soybean meal-whey-based diet for nursery pigs

Three trials were carried out with pigs between 5 and 8 wk of age to determ ine the limiting order of amino acids in a 13.5% CP corn-soybean meal-based diet containing 8% dried whey. The positive-control diet was a 19.2% CP co rn-soybean meal-based diet (1.15% lysine), also with 8% dried whey. Amino a cid additions to the low-protein, negative-control diet were based on level s needed to accomplish 110% of ideal ratios (to lysine, set at 1.15%). In E xp. 1, the addition of an amino acid mixture containing Lys, Trp, Thr, Met, Ile, and Val to the low-protein diet increased(P <.05) gain and gain: feed ratio, and these response traits were not different from those of pigs fed the 19.2% CP positive-control diet. Single deletion of Lys from the supple mental amino acid mixture depressed performance to a greater (P <.05) exten t than single deletion of any of the other amino acids. Single deletions of Trp, Thr, Met, or Val decreased (P <.05) performance in a similar but less er magnitude than the decrease caused by Lys deletion, whereas Ile deletion was without effect. Experiments 2 and 3 were designed to evaluate the limi ting order of AA beyond Lys in the low-protein diet. Neither His nor Glu we re found to be deficient, and, as in Exp. 1, deletion of Trp, Thr, Met, or Val from the supplemental amino acid mixture resulted in performance depres sions (P <.05) that were similar. The results suggest that Lys is first-lim iting and Trp, Thr, Met, and Val are equally second-limiting in a reduced p rotein (13.5% CP) corn-soybean meal-based diet with 8% whey for 10-kg pigs.