Effects of dietary leucine excess and leucine metabolites supplementation on growth and immune response of weanling pigs

摘要

Three experiments involving 152 pigs (6 kg and 24-d-old) were conducted to study the effects of excess dietary leucine (LEU) or dietary supplementation with LEU catabolites, [alpha]-ketoisocaproic acid (KIC) and [beta]-hydroxy-methyl-butyrate (HMB) on growth and immune response. In Experiments 1 and 2, pigs were fed either diets consisting of a basal wheat-oat groats-menhaden fish meal-dried whey diet that provided 1.12% LEU, to which 1.12% synthetic LEU, 1.12% KIC or.4% HMB were added or corn-soybean meal-dried whey (C-SBM-DW) diets. In Experiment 3, pigs were assigned to four treatments in a 2 x 2 factorial arrangement. Treatments consisted of two levels of dietary LEU and a daily i.m. injection of either 150 [mu]g dexamethasone (DXM) x kg[superscript]-1 BW or the corresponding amount of saline. Pigs were fed a basal C-SBM-DW diet (1.56% LEU) or one to which 1.56% synthetic LEU was added. The experiments lasted 9 wk (Experiment 1), 6 wk (Experiment 2) or 4 wk (Experiment 3). Criteria studied included growth performance, plasma free amino acids, immunoglobulins (IgG and IgM) against keyhole limpet hemocyanin (KLH) and whole blood (Experiments 1 and 2) or isolated peripheral lymphocyte blastogenesis (Experiment 3). In Experiment 1, addition of LEU or KIC to diets had no effects (P \u3c.05) on any of the criteria studied. In Experiment 2, addition of LEU to diets increased (P \u3c.05) plasma free LEU and PUN. Addition of either LEU or KIC decreased (P \u3c.05) plasma free VAL and ILE. In Experiment 3, addition of LEU to diets increased (P \u3c.05) plasma free LEU and decreased (P \u3c.05) ADG, ADFI, plasma free ILE and VAL and IgG against KLH at wk 3. Daily DXM injection increased (P \u3c.05) plasma free LEU and PUN and decreased (P \u3c.05) gain to feed ratio and IgG against KLH at wk 3. Results from these experiments indicate that LEU concentrations encountered in practical diets do not cause detrimental effects on growth and immune response. However, the high LEU concentration used in Experiment 3 may be detrimental for both growth and immune response.