Early intestinal development is essential for chicken embryos to fulfill their maximal growth potential. Mannan oligosaccharide (MOS) is known to improve gut morphology, function, and innate immunity; therefore, we hypothesized that its administration in the prehatch period to the sterile intestine of embryos would affect intestinal development and functionality without mediation of gut microflora. The MOS was administered by in ovo feeding procedure to embryos 3 d before hatch. the effects of MOS administration on intestinal morphology, activity of the brush-border enzymes amino peptidase (AP) and sucrase isomaltase (SI) and mRNA abundance of AP, SI, sodium-dependent glucose cotransporter 1 (SGLT1), peptide transporter 1 (PepT1), secreted mucin (MUC2), and toll-like receptors (TLR2 and TLR4) were examined and compared with saline-injected and noninjected controls. Results show that on embryonic d 20 the only parameter affected was MUC2 mRNA abundance, which exhibited a 3-fold increase in the MOS group versus controls. On day of hatch more parameters were affected: a 20 to 32% increase in villus area was found in the MOS group compared with controls; crypt depth and number of goblet cells per villus were higher by 20 and 50%, respectively, compared with the saline group; and AP and SI activities were higher by 44 and 36%, respectively, compared with the noninjected control. In addition, an increase in fold change mRNA abundance of AP, SI, and TLR4 was observed in the MOS group compared with controls. However, on d 3 posthatch, a decrease in MOS effects was noted, indicating a temporally limited effect after administration of 1 dose. In ovo administration of MOS prehatch resulted in a hatching chick with more mature enterocytes and enhanced epithelial barrier and digestive and absorptive capacity at day of hatch. Results imply that the mechanism underlying the observed changes is not mediated through gut microflora but rather involves a direct effect of MOS on intestinal cells.

A germ-free (GF) chicken model was used to test 2 hypotheses: 1. microbial colonization of the gastrointestinal tract (GIT) influences mucin gene expression and mucin types; and 2. mannan oligosaccharide (MOS) supplementation affects GIT cells directly, without bacteria mediation, compared with bacterial-mediated effect (i.e., indirectly). Gnotobiotic isolators were used: 1) GF, 2) with a single bacteria population, and 3) conventionalized by exposure to cecal bacterial contents. Each was divided to 2 diet groups: with or without MOS (2 kg/t) for 1 wk. Results show that the absence of bacteria in the GIT caused a reduction in neutral and acidic goblet cell (GC) number and density, an increase in sulfated mucin, absence of sialylated GC, and reduced mucin 2 mRNA expression in the small intestine of GF compared with conventional birds. These results indicate a reduced development of mucin production and secretion in the absence of GIT bacteria implying a less mature small intestine mucosa, supporting our first hypothesis. Results from the single bacteria population group were not conclusive and did not support any of the hypotheses. Supplementation of MOS, regardless of microbial presence, caused a reduction in neutral GC number and density but increased neutral GC area. The MOS caused different effects on acidic mucins in conventional and GF birds, causing a reduction in sialylated GC number (conventional) and a reduction in sulfated GC density (GF), all supporting a direct effect of MOS in GF animals, in addition to an indirect effect via gut microflora.

Taste perception is a crucial biological mechanism affecting food and water choices and consumption in the animal kingdom. Bitter taste perception is mediated by a G-protein-coupled receptor (GPCR) family-the taste 2 receptors (T2R)-and their downstream proteins, whereas sweet and umami tastes are mediated by the GPCR family -taste 1 receptors (T1R) and their downstream proteins. Taste receptors and their downstream proteins have been identified in extra-gustatory tissues in mammals, such as the lungs and gastrointestinal tract (GIT), and their GIT activation has been linked with different metabolic and endocrinic pathways in the GIT. The chicken genome contains three bitter taste receptors termed ggTas2r1, ggTas2r2, and ggTas2r7, and the sweet/umami receptors ggTas1r1 and ggTas1r3, but it lacks the sweet receptor ggTas1r2. The aim of this study was to identify and determine the expression of genes related to taste perception in the chicken GIT, both at the embryonic stage and in growing chickens. The results of this study demonstrate for the first time, using real-time PCR, expression of the chicken taste receptor genes ggTas2r1, ggTas2r2, ggTas2r7, ggTas1r1, and ggTas1r3 and of their downstream protein-encoding genes TRPM5, α-gustducin, and PLCβ2 in both gustatory tissues-the palate and tongue, and extra-gustatory tissues-the proventriculus, duodenum, jejunum, ileum, cecum, and colon of embryonic day 19 (E19) and growing (21 d old) chickens. Expression of these genes suggests the involvement of taste pathways for sensing carbohydrates, amino acids and bitter compounds in the chicken GIT.

Bitter taste is one of the basic taste modalities, warning against consuming potential poisons. Bitter compounds activate members of the bitter taste receptor (Tas2r) subfamily of G protein-coupled receptors (GPCRs). The number of functional Tas2rs is species-dependent. Chickens represent an intriguing minimalistic model, because they detect the bitter taste of structurally different molecules with merely three bitter taste receptor subtypes. We investigated the binding modes of several known agonists of a representative chicken bitter taste receptor, ggTas2r1. Because of low sequence similarity between ggTas2r1 and crystallized GPCRs (~10% identity, ~30% similarity at most), the combination of computational approaches with site-directed mutagenesis was used to characterize the agonist-bound conformation of ggTas2r1 binding site between TMs 3, 5, 6 and 7. We found that the ligand interactions with N93 in TM3 and/or N247 in TM5, combined with hydrophobic contacts, are typically involved in agonist recognition. Next, the ggTas2r1 structural model was successfully used to identify three quinine analogues (epiquinidine, ethylhydrocupreine, quinidine) as new ggTas2r1 agonists. The integrated approach validated here may be applicable to additional cases where the sequence identity of the GPCR of interest and the existing experimental structures is low.

The sense of taste has a key role in nutrient sensing and food intake in animals. A standardized and simple method for determination of tastant-detection thresholds is required for chemosensory research in poultry. We established a 24-h, 2-alternative, forced-choice solution-consumption method and applied it to measure detection thresholds for 3 G-protein-coupled receptor-mediated taste modalities-bitter, sweet, and umami-in chicken. Four parameters were used to determine a significant response: 1) tastant-solution consumption; 2) water (tasteless) consumption; 3) total consumption (tastant and water together); 4) ratio of tastant consumption to total consumption. Our results showed that assignment of the taste solutions and a water control to 2 bottles on random sides of the pen can be reliably used for broiler chicks, even though 47% of the chicks groups demonstrated a consistently preferred side. The detection thresholds for quinine (bitter), L-monosodium glutamate (MSG) (umami), and sucrose (sweet) were determined to be 0.3 mM, 300 mM, and 1 M, respectively. The threshold results for quinine were similar to those for humans and rodents, but the chicks were found to be less sensitive to sucrose and MSG. The described method is useful for studying detection thresholds for tastants that have the potential to affect feed and water consumption in chickens.