Nutritional needs of non-essential amino acids for intestinal health and growth performance of nursery pigs fed diets without soybean meal.

The objective was to investigate the impact of graded levels of non-essential amino acids (NEAA) in soybean meal (SBM)-free diets on intestinal health and growth of nursery pigs. Thirty-two pigs weaned on d 21 of age with body weight (BW) of 6.7 ± 0.1 kg were assigned to one of four diets in a randomized complete block design with BW and sex as blocks. Pigs were fed for 28 d in 3 phases (10, 12, and 6 d, respectively). The diets consisted of a typical corn-SBM diet with supplemental lysine, methionine, and threonine, containing SBM at 19%, 22%, and 27% in phases 1, 2, and 3, respectively (NC), and SBM-free diets supplemented with 0% (PC), 50%, and 100% of NEAA provided by SBM in the NC. All diets met the requirements of essential amino acids. Pigs were housed individually and euthanized on d 28 to collect the jejunal tissue and mucosa to determine the jejunal mucosa-associated microbiota and immunity. The PROC MIXED of SAS was used with treatment as a fixed effect and initial BW and sex as random effects. Contrasts were used to compare the NC and PC and determine linear effects of NEAA levels. The PC reduced (P < 0.05) the expression of toll-like receptors 2 and 4 in the jejunum compared with the NC. Increasing NEAA tended to linearly increase (P = 0.075) the expression of toll-like receptor 4 and linearly increased (P < 0.05) the expression of cluster of differentiation 14 in the jejunum. The PC increased (P < 0.05) interleukin-8 but reduced (P < 0.05) immunoglobulin A in the jejunal mucosa compared with the NC. Increasing NEAA linearly reduced (P < 0.05) interleukin-8 but increased (P < 0.05) immunoglobulin A. The PC reduced (P < 0.05) fecal nitrogen excretion from d 22 to 28 compared with the NC. The PC reduced (P < 0.05) weight gain and gain:feed from d 0 to 28 compared with the NC. Increasing NEAA linearly increased (P < 0.05) weight gain from d 22 to 28 and gain:feed from d 0 to 28. In conclusion, feeding the SBM-free diet meeting requirements of essential amino acids reduced fecal nitrogen excretion but impaired jejunal immune responses and growth compared with pigs fed the NC. Increasing NEAA improved jejunal immune responses and growth, and at least 100% of the NEAA levels provided by SBM in the typical corn-SBM diet with supplemental lysine, methionine, and threonine may be necessary to optimize growth in nursery pigs fed SBM-free diets.