Effects of dietary glycyl-glutamine on growth performance, small intestinal integrity, and immune responses of weaning piglets challenged with lipopolysaccharide

The objectives of this study were to determine the effects of dietary glycyl-glutamine (Gly-Gln) on postweaning growth, small intestinal morphology, and immune response of stressed or nonstressed piglets. Pigs (n = 144; initially 4.49 kg and 14 d of age) were randomly allocated to 24 pens (6 pigs/pen) in an environmentally controlled nursery and assigned to Escherichia coli lipopolysaccharide (LPS) challenge (PBS vs. LPS) and Gly-Gln supplementation (0 vs. 0.15%) in a 2 x 2 factorial arrangement of treatments with 6 pens/treatment. The LPS was the stress-inducing agent, and it was injected on d 7 and 14 of the 21-d experiment. Inflammatory challenge with LPS reduced ADG (P < 0.05) and tended to reduce ADFI (P = 0.06) of piglets from d 7 to 21 of the experiment. Supplementation of Gly-Gln increased ADG and G: F from d 0 to 21 (P < 0.05). On d 21 (1 wk after the second LPS injection), there was an LPS challenge x diet Gly-Gln interaction for ADFI (P < 0.05), but it was difficult to ascertain whether Gly-Gln increased ADFI. A trend for an LPS challenge x diet Gly-Gln interaction was observed for ADG (P = 0.07). There were no differences in lymphocyte proliferation among treatments. The LPS challenge increased crypt depth (CD) of the duodenum and decreased the ratio of villus height (VH) to CD of the ileum (P < 0.05) on d 14 (1 wk after the first LPS injection), whereas dietary supplementation of Gly-Gln increased VH of the ileum and VH: CD of the duodenum (P < 0.05). The concentration of peripheral blood IL-1 beta was increased by injection of LPS (P < 0.05) and was decreased by dietary Gly-Gln supplementation during the experimental period (P < 0.05); however, there was no interaction of LPS challenge x Gly-Gln addition for IL-1 beta concentration. Concentrations of peripheral blood IL-2 tended to increase at d 14 (P = 0.09) and soluble IL-2 receptor tended to decrease at d 7 (P = 0.06) in piglets supplemented with Gly-Gln; therefore, the peripheral blood IL-2/soluble IL-2 receptor system tended to favor the secretion of IL-2 during the first 2 wk of the experiment. In conclusion, considerable suppression of growth and immune function occurred in early weaning piglets challenged with LPS, and such depression could be alleviated by dietary Gly-Gln supplementation independent of the LPS challenge.