Functional Difference of Free L-Lysine and L-Lysine HCl on Growth Performances, Intestinal Health, and Intestinal Integrity in Newly Weaned Pigs

This study was conducted to evaluate functional difference of liquid based free L-Lys and crystalline L-Lys HCl on the growth performances, intestinal health, and intestinal integrity in newly weaned pigs. Twenty four newly weaned pigs at 21 d of age (5.9 ± 0.1 kg BW), were randomly allotted to 2 treatments with 12 pens (1 pig per pen, 6 barrow and 6 gilt pens) per treatment, and fed experimental diets for 3 wk based on 2 phases (phase 1 for 10 d; and phase 2 for 11 d). Two treatments were, (1) a diet supplemented with crystalline L-Lys HCl (0.45%, Daesang Corp., Seoul, Korea) or (2) a diet supplemented with liquid based free L-Lys (0.71%, Daesang Corp., Seoul, Korea). These 2 diets were formulated to have equal SID Lys content and nutrients meeting the NRC requirements (2012). Body weight and feed disappearance were measured on d 7, 10, and 21 to calculate ADG, ADFI, and G:F ratio. Blood samples were taken on d 20 to obtain plasma. At the end of wk 3, all pigs were euthanized to obtain gut tissues and mucosal tissues from duodenum and jejunum. Plasma and mucosal tissues were used to measure tumor necrosis factor alpha (TNF-α), protein carbonyl, malondialdehyde, 8-OHdG, and total antioxidant capacity (TAC). Gut tissues were fixed for histological evaluation of gut morphology, for immunohistochemistry of Ki-67 protein to measure enterocyte proliferation, and for Western blot to quantify tight junction proteins (ZO-1, claudin-1, and occludin). Data were analyzed using PROC MIXED procedure in SAS with pen as the experimental unit and P values < 0.05 considered significant and < 0.10 considered tendency. Overall, source of Lys (free L-Lys vs. crystalline L-Lys HCl) did not affect ADG (0.319 and 0.319 kg/d), ADFI (0.384 and 0.397 kg/d), and G:F (0.828 and 0.804) of pigs. Liquid based free L-Lys decreased (P < 0.05) jejunal TNF-α (1.05 to 0.81 pg/mg protein), and plasma TNF-α (130 to 110 pg/mg protein) without affecting concentrations of protein carbonyl, malondialdehyde, and TAC. Liquid based free L-Lys increased (P < 0.05) villus height (346 to 386 µm) and villus height:crypt depth ratio (1.21 to 1.37 μm) in the jejunum. Collectively, this study indicates that free L-Lys supplementation improves intestinal health potentially by decreasing of systemic inflammatory status and improving jejunal morphology compared with the use of L-Lys HCl in newly weaned pigs.