Intestinal mucosa is the interface between the microbial content of the gut and the host’s milieu. The goal of this study was to modulate chicken intestinal microflora by in ovo stimulation with galactooligosaccharides (GOS) prebiotic and to demonstrate the molecular responses of the host. The animal trial was performed on meat-type chickens (Ross 308). GOS was delivered by in ovo injection performed into the air cell on day 12 of egg incubation. Analysis of microbial communities and mucosal gene expression was performed at slaughter (day 42 post-hatching). Chyme (for DNA isolation) and intestinal mucosa (for RNA isolation) from four distinct intestinal segments (duodenum, jejunum, ileum, and caecum) was sampled. The relative abundance of Bifidobacterium spp. and Lactobacillus spp. in DNA isolated from chyme samples was determined using qPCR. On the host side, the mRNA expression of 13 genes grouped into two panels was analysed with RT-qPCR. Panel (1) included genes related to intestinal innate immune responses ( IL-1β , IL-10 and IL-12p40 , AvBD1 and CATHL2 ). Panel (2) contained genes involved in intestinal barrier function ( MUC6 , CLDN1 and TJAP1 ) and nutrients sensing ( FFAR2 and FFAR4 , GLUT1 , GLUT2 and GLUT5 ). GOS increased the relative abundance of Bifidobacterium in caecum (from 1.3% to 3.9%). Distinct effects of GOS on gene expression were manifested in jejunum and caecum. Cytokine genes ( IL-1β , IL-10 and IL-12p40 ) were up-regulated in the jejunum and caecum of the GOS-treated group. Host defence peptides ( AvBD1 and CATHL2 ) were up-regulated in the caecum of the GOS-treated group. Free fatty acid receptors ( FFAR2 and FFAR4 ) were up-regulated in all three compartments of the intestine (except the duodenum). Glucose transporters were down-regulated in duodenum ( GLUT2 and GLUT5 ) but up-regulated in the hindgut ( GLUT1 and GLUT2 ). In conclusion, GOS delivered in ovo had a bifidogenic effect in adult chickens. It also modulated gene expression related to intestinal immune responses, gut barrier function, and nutrient sensing.

In ovo delivery of prebiotics and synbiotics in chickens allows for the development of intestinal microflora prior to hatching, which boosts their robustness. The goal of this study was to determine the transcriptomic profile of the spleen (S), cecal tonsils (CT), and large intestine (LI) of adult chickens injected with prebiotics and synbiotics in ovo. On day 12 of embryo development, incubating eggs were injected with prebiotics: inulin alone (P1) or in combination with Lactococcus lactis subsp. lactis IBB2955 (S1), galactooligosaccharides (GOS) alone (P2) or in combination with Lactococcus lactis subsp. cremoris IBB477 (S2); control group (C) was mock injected with physiological saline. Gene expression analysis was conducted using an Affymetrix Chicken Gene 1.1 ST Array Strip. Most of the differentially expressed genes (DEG) were detected in the cecal tonsils of P2 (378 DEG), and were assigned to gene ontology categories: lymphocyte proliferation, activation and differentiation, and cytokine production. Ingenuity pathway analysis of the DEG (CT of P2) indicated the inhibition of humoral and cellular immune responses, e.g., role of NFAT in regulation of immune responses, phagocytosis, production of nitric oxide, NF-κB, IL-8, and CXCR4 signaling. The DEG with the highest up-regulation from S1 and P2 were involved in gene expression (PAPOLA, RPL27A, RPLP1, and RPS29) from P1 and P2 in transport (BEST4, SLC9A3, and SLC13A2), metabolism (OGT, ALPP, CA4, and CA7), signaling (FGG, G3BP2, UBB, G3BP2, CACNA1G, and ATP6V0A4), and immune responses (MSMB, LGALS3, CABIN1, CXCR5, PAX5, and TNFRSF14). Two DEG influencing the complement system (SERPING1 and MIR1674) were down-regulated in P2 and S1. In conclusion, GOS injected in ovo provided the most potent stimulation of the host transcriptome. This is likely due to its strong bifidogenic effect, which triggers proliferation of indigenous embryonic microflora in ovo, and indirectly influences gene expression regulation in host tissues, especially cecal tonsils.

Prebiotics and probiotics applied alone or together (synbiotics) can influence the intestinal microbiota and modulate the immune response. We analyzed the impact of in ovo administration of synbiotics on immune system development in Ross (broiler) and Green-legged Partridgelike (GP, dual-purpose fowl) chickens. For in ovo delivery on the 12 th day of the eggs incubation, two strains of lactic acid bacteria (LAB) were used, i.e. Lactococcus lactis subsp. lactis IBB SL1 (S1) and Lactococcus lactis subsp. cremoris IBB SC1 (S2), combined with raffinose family oligosaccharides (RFO) prebiotic. Other treatments included in ovo delivery of commercial synbiotic (S3), RFO prebiotics alone (P) and physiological saline (C). Immune system development was analyzed by relative weight (indices) and histology of the lymphatic organs (bursa of Fabricius, thymus and spleen) at two time points (3 rd and 6 th week of life). The results indicate that the development of the lymphatic organs was significantly affected by in ovo treatment. The bursa and bursa to spleen index was higher in P and S2 groups of broilers (P<0.05) when compared to S3. In GP at the 3 rd week of age, the spleen index was significantly higher in S2 (P<0.05). The histological image of the thymus displayed an increase of thymocytes in the cortex in all synbiotic-treated groups (S1, S2, S3). In ovo delivery of synbiotics is an efficient mode of immune system stimulation in chickens but its efficiency depends on chicken genotype.

OBJECTIVE To evaluate the effect of in ovo administration of inulin and Lactococcus lactis on immune-related gene expression in broiler chickens. ANIMALS 45 Ross broilers. PROCEDURES On day 12 of embryonic development, 360 eggs were equally allocated among 3 treatment groups and injected with 0.2 mL of a solution that contained 1.76 mg of inulin (prebiotic group) or 1.76 mg of inulin enriched with 1,000 CFUs of L lactis subsp lactis 2955 (synbiotic group), or they were injected with 0.2 mL of saline (0.9% NaCl) solution (control). At 1, 14, and 35 days after hatching, 5 male birds from each group were euthanized, and the spleen and cecal tonsils were harvested for determination of interleukin (IL)-4, IL-6, IL-8, IL-12p40, IL-18, cluster of differentiation 80, interferon-β, and interferon-γ expression by means of a reverse transcription quantitative PCR assay. Gene expressions in the cecal tonsils and spleens of chickens in the prebiotic and synbiotic groups were compared with those of control chickens at each tissue collection time. RESULTS Compared with control birds, immune-related gene expression was downregulated in birds in the prebiotic and synbiotic groups, and the magnitude of that downregulation was more pronounced in the cecal tonsils than in the spleen and increased with age. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that in ovo administration of a prebiotic or synbiotic to broilers was associated with downregulation of immune-related gene expression in the cecal tonsils and spleen. The magnitude of that downregulation increased with age and was most likely caused by stabilization of the gastrointestinal microbiota.