Abstract Non-essential amino acids (NEAA) are mostly sufficient in typical pig diets and can also be provided by the conversion from other amino acids and nitrogen sources, and therefore, supplementation of NEAA is not likely needed unless the diet has limited amino acids and nitrogen sources. It is hypothesized that NEAA are nutritionally deficient, impairing intestinal health and growth of nursery pigs when the use of protein supplements is restricted in the diet and that increasing NEAA supplementation at a certain level may indicate potential needs. The objective of this study was to investigate the impact of graded levels of NEAA in soybean meal (SBM)-free diets on intestinal health and growth of nursery pigs. Thirty-two weaned pigs weaned on d 21 of age (BW = 6.7 ± 0.1 kg) were assigned to one of four diets in a randomized complete block design with initial 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 corn–SBM diet containing SBM at 19%, 22%, and 27% in phases 1, 2, and 3, respectively (NC), and SBM-free diets supplemented with NEAA at 0% (PC), 50%, and 100% of the levels that would have been provided by SBM. All diets were formulated to meet the essential amino acid requirements provided by NRC (2012). Pigs were housed individually and euthanized on d 28 to collect the jejunal tissue and mucosa. Pre-planned contrasts were used to compare NC and PC and determine linear effects of dietary NEAA levels. Increasing dietary NEAA levels linearly increased (P 0.05) the abundance of Proteobacteria, Succinivibrionaceae, and Acidaminococcaceae in the jejunal mucosa. The PC reduced (P 0.05) the expression of toll-like receptor 2 and 4 in the jejunum compared with NC. Increasing dietary NEAA levels 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 NC. Increasing dietary NEAA levels linearly reduced (P 0.05) interleukin-8 but increased (P 0.05) immunoglobulin A. The PC reduced (P 0.05) weight gain and gain:feed from d 0 to 28 compared with NC. Increasing dietary NEAA levels linearly increased (P 0.05) daily gain from d 22 to 28 and gain:feed from d 0 to 28. In conclusion, gradual increase in dietary NEAA levels improves jejunal immune responses and growth performance, and NEAA level greater than 50% of that provided by SBM may be required to achieve outcomes similar to corn-SBM diets in nursery pigs fed SBM-free diets.
Sung et al. (Wed,) studied this question.
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