Microbiota but not immune modulation by a pro- and postbiotic was associated with the diet-additive interaction in broilers.

This study investigated the diet-additive interactions of a Lactobacilli-based probiotic (Pro) and postbiotic (Post) on immune parameters and cecal microbiota composition, with subsequent effects on the metabolome in broilers. A completely randomized block design was employed with 2 diets [standard (SD), and challenge (CD)] and 3 additive conditions (Control, Pro, Post) involving 1,368 one-day-old male Ross 308 broilers equally distributed among 36 pens in a 42 d study. Diets were formulated to contain identical nutrient levels, with CD higher than SD in non-starch polysaccharide content by including rye and barley. Total non-specific serum Ig A, M and G concentrations were determined weekly from d14 to 35. Following vaccination, titres of specific antibodies binding Newcastle disease virus (NDV) and infectious bursal disease virus (IBDV) were measured. Microbiota composition was analyzed by 16S rRNA gene sequencing at d14 and 35, and α- and ß-diversity indexes (Observed, Chao1, Bray, Jaccard) were calculated. Cecal short-chain fatty acids and the semi-polar metabolome were determined in the Control SD and all CD groups at d35. At d35, a diet-additive interaction was observed on cecal microbiota composition. Within SD, Pro and Post did not affect operational taxonomic units (OTU) abundance (adjusted-P > 0.05) and diversity indexes (P > 0.05). Within CD, Pro and Post affected the relative abundances of 37 and 44 OTUs, respectively (adjusted-P < 0.05), with Post but not Pro affecting ß-diversity indexes (P = 0.041 and 0.064 for Bray and Jaccard, respectively). Within CD, Post increased cecal acetate (21%; P = 0.007) and butyrate (41%; P = 0.002) concentration and affected the concentration of 2 metabolites (adjusted-P < 0.05), while Pro affected 240 metabolites (adjusted-P < 0.05). No diet-additive interactions were observed on serum Ig (P > 0.05), except for IgM at d14 (P = 0.004). Diet composition, but not the additives, affected immune status parameters. The Pro and Post affected cecal microbiota composition only under dietary challenging conditions as previously reported for growth.

Caecal microbiota composition of experimental inbred MHC-B lines infected with IBV differs according to genetics and vaccination.

Interactions between the gut microbiota and the immune system may be involved in vaccine and infection responses. In the present study, we studied the interactions between caecal microbiota composition and parameters describing the immune response in six experimental inbred chicken lines harboring different MHC haplotypes. Animals were challenge-infected with the infectious bronchitis virus (IBV), and half of them were previously vaccinated against this pathogen. We explored to what extent the gut microbiota composition and the genetic line could be related to the immune response, evaluated through flow cytometry. To do so, we characterized the caecal bacterial communities with a 16S rRNA gene amplicon sequencing approach performed one week after the IBV infectious challenge. We observed significant effects of both the vaccination and the genetic line on the microbiota after the challenge infection with IBV, with a lower bacterial richness in vaccinated chickens. We also observed dissimilar caecal community profiles among the different lines, and between the vaccinated and non-vaccinated animals. The effect of vaccination was similar in all the lines, with a reduced abundance of OTU from the Ruminococcacea UCG-014 and Faecalibacterium genera, and an increased abundance of OTU from the Eisenbergiella genus. The main association between the caecal microbiota and the immune phenotypes involved TCRϒδ expression on TCRϒδ+ T cells. This phenotype was negatively associated with OTU from the Escherichia-Shigella genus that were also less abundant in the lines with the highest responses to the vaccine. We proved that the caecal microbiota composition is associated with the IBV vaccine response level in inbred chicken lines, and that the TCRϒδ+ T cells (judged by TCRϒδ expression) may be an important component involved in this interaction, especially with bacteria from the Escherichia-Shigella genus. We hypothesized that bacteria from the Escherichia-Shigella genus increased the systemic level of bacterial lipid antigens, which subsequently mitigated poultry γδ T cells.