Intestinal permeability, microbiota composition, and expression of genes related to intestinal barrier function of broiler chickens fed different methionine sources supplemented at varying concentrations

Intestinal health of broiler chickens is influenced by the concentration of dietary amino acids but data are limited on the role of dietary methionine (Met). Two experiments were conducted to investigate the implications of different Met sources for perfor-mance, gut barrier function, and intestinal microbiota in broilers. In the first experiment, Ross 308 off-sex birds (n = 900) were assigned to 10 dietary treatments each replicated 9 times in a 35-day study. Three sources of Met included DL-Met, L-Met, or Met hydroxy ana-log free acid (MHA-FA), each supplemented at sub-optimal (SUB) at 80%, adequate (ADE) at 100% and over-requirement (OVR) at 120% of the specifications against a deficient (DEF) diet with no added Met. The second experiment used 96 Ross 308 broilers in a 2 pound 4 factorial arrangement. Four diets included 3 sources of Met supplemented at ADE level plus the DEF treat-ment. On d 17, 19, and 23, half of the birds in each die-tary treatment were injected with dexamethasone (DEX) to induce leaky gut. In the first experiment, without an interaction, from d 0 to 35, birds fed DL-Met and L-Met performed similarly for BWG, feed intake, and FCR but birds fed MHA-FA had less feed intake and BWG (P < 0.05). At d 23, mRNA expres-sion of selected tight junction proteins was not affected except for claudin 2. Ileal microbiota of DEF treatment was different from DL-MET or L-MET supplemented birds (P < 0.05). However, microbiota of MHA-FA treatments was only different at OVR from the DEF group. The abundance of Peptostreptococcus increased in DEF treatment whereas Lactobacillus decreased. In the second experiment, DEX independently increased (P < 0.001) intestinal permeability assayed by fluores-cein isothiocyanate dextran, but diet had no effect. DL-Met and L-Met fed birds had a higher level of clau-din 3 only in DEX-injected birds (P < 0.05). In conclu-sion, unlike the level of supplementation, DL-Met, L-Met, and MHA-FA were largely similar in their lim-ited impacts on intestinal barrier function and gut microbiota in broilers.