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Intestinal mucus plays important roles in protecting the epithelial surfaces against pathogens, supporting the colonization with commensal bacteria, maintaining an appropriate environment for digestion, as well as facilitating nutrient transport from the lumen to the underlying epithelium. The mucus layer in the poultry gut is produced and preserved by mucin-secreting goblet cells that rapidly develop and mature after hatch as a response to external stimuli including environmental factors, intestinal microbiota as well as dietary factors. The ontogenetic development of goblet cells affects the mucin composition and secretion, causing an alteration in the physicochemical properties of the mucus layer. The intestinal mucus prevents the invasion of pathogens to the epithelium by its antibacterial properties (e.g. β-defensin, lysozyme, avidin and IgA) and creates a physical barrier with the ability to protect the epithelium from pathogens. Mucosal barrier is the first line of innate defense in the gastrointestinal tract. This barrier has a selective permeability that allows small particles and nutrients passing through. The structural components and functional properties of mucins have been reviewed extensively in humans and rodents, but it seems to be neglected in poultry. This review discusses the impact of age on development of goblet cells and their mucus production with relevance for the functional characteristics of mucus layer and its protective mechanism in the chicken’s intestine. Dietary factors directly and indirectly (through modification of the gut bacteria and their metabolic activities) affect goblet cell proliferation and differentiation and can be used to manipulate mucosal integrity and dynamic. However, the mode of action and mechanisms behind these effects need to be studied further. As mucins resist to digestion processes, the sloughed mucins can be utilized by bacteria in the lower part of the gut and are considered as endogenous loss of protein and energy to animal. Hydrothermal processing of poultry feed may reduce this loss by reduction in mucus shedding into the lumen. Given the significance of this loss and the lack of precise data, this matter needs to be carefully investigated in the future and the nutritional strategies reducing this loss have to be defined better.

The current study investigated the impacts of supplementation of post-weaning piglet diets with Macleaya cordata extract (MCE) and naringin (NAR) on performance, nutrient digestibility and intestinal histomorphology. Post-weaning crossbred piglets (28 males and 28 females; age at weaning 25 d) were randomly allotted to 28 pens. The experiment consisted of a control and three treatment groups (MCE60, MCE120 and NAR). For diets MCE60 and MCE120, the control diet was supplemented with 60 and 120 mg Sangrovit® Extra (a standardised premixture of MCE) per kg diet, respectively. Group NAR received 50 mg pure NAR per kg diet. The experiment lasted 42 d (d 25 - 66 of age). At d 66, apparent pre-caecal digestibility (APD) of nutrients was determined and histomorphological changes in mid-jejunum were evaluated. Feeding diets MCE120 and NAR improved body weight gain and feed conversion ratio of piglets. After feeding diets MCE120 and NAR, the APD of phosphorus and different single and total amino acids were greater than after feeding the control diet. The present data demonstrated that supplementation of post-weaning piglet diets with 120 mg MCE or 50 mg NAR per kg diet could improve growth performance and nutrient digestibility and had no impact on histomorphological variables in the jejunum. These findings indicate the potential of these products to be used as growth promoters in pig nutrition.

A novel three-step combination of in vitro and ex vivo screening was established to massively screen host derived lactic acid bacteria (LAB) from the broiler chicken intestine with inhibitory activity against Escherichia coli. In a first step, a massive sample pool consisting of 7102 broiler-derived colonies from intestinal contents were established and sub-cultured. Supernatants thereof were incubated with an E. coli model strain to screen suitable isolates with inhibitory activity. A total of 76 isolates of interest were subsequently further studied based on either pH dependent or -independent activity in the second step of the assay. Here, in-depth growth inhibition of the E. coli model strain and the potential of isolates for lactic acid production as inhibitory substance were indexed for all isolates. Resulting scatter plots of both parameters revealed five isolates with exceptional inhibitory activity that were further studied under ex vivo condition in the third step of the assay. These isolates were taxonomically classified as strains of the species Lactobacillus agilis, Lactobacillus salivarius, and Pediococcus acidilactici. Samples from the broiler chicken intestine were inoculated with the Lactobacillus isolates and the E. coli model strain. After 8 and 24 h incubation, respectively, growth of the E. coli model strain was monitored by cultivation of the E. coli strain in antibiotic supplemented medium. By their superior inhibitory activity against the E. coli model strain, one L. agilis and one L. salivarius strain were selected and characterized for further application as probiotics in broiler chicken. Additionally, their antibiotic resistance patterns and resilience under gastric stress of isolates were also characterized. The results of this study demonstrate that the novel isolation procedure was able to efficiently and rapidly isolate and identify bacterial strains from a massive sample pool with inhibitory potential against specific types of bacteria (here E. coli). The introduction of the final ex vivo selection step additionally confirmed the inhibitory activity of the strains under conditions simulating the intestinal tract of the host. Furthermore, this method revealed a general potential for the isolation of antagonistic strains that active against other pathogenic bacteria with specific biomarker.

Hydrothermal processing (HTP) of poultry feed including pelleting, extrusion and expansion, have a considerable impact on feed hygiene, nutrient availability as well as on intestinal morphology and microbiota. While hydrothermal processes are effective strategies for hygienizing of the feed contaminated with non-spore-forming bacteria, processed feed is at the risk of recontamination, particularly during the cooling process. However, the impact of hydrothermal treatments on gut microbiota can be mostly confined to lactobacilli and their main metabolite, lactate, in the proximal part of the gastrointestinal tract (GIT), particularly crop. The effect of HTP on nutrients availability is equivocal. The effect of hydrothermal processes on macro-nutrients such as starch, fat and protein is mostly negligible. However, most of vitamins (Vit), enzymes and anti-nutritional factors (ANF) e.g. enzyme inhibitors, lectins and phytate are prone to be reduced. The impact of hydrothermal treatments on starch gelatinization of feed is not substantial and gelatinization does not play a considerable role in starch digestion of a processed feed. Ileal starch digestibility of a processed feed is greatly dependent on the starch and non-starch polysaccharides profile of the feed ingredients, processing variables and their interactions. In contrast to the common believe, there has been no clear indication showing that, the beneficial impact of HTP on protein digestibility is through protein denaturation. Pelleting process seems to have no beneficial impact on amino acid (AA) digestibility. However, depending on the ingredients composition of the diet, the probability for improving AA digestibility by expansion and extrusion (HTST) processes can be considerable, especially when ingredients with high concentration of ANF are treated. Furthermore, the putative deleterious impact of the HTST processes on AA digestibility of poultry feed, through AA degradation and Maillard reactions, seems to be not pertinent. The harmful impact of the processes on the other thermolabile nutrients such as Vit cannot be ignored. There seems to be a lack of consistency in the effects of hydrothermal treatments on absorption, retention and deposition of minerals (Min) in poultry feed. Higher feed intake (FI) and passage rate (PR) usually coincide with feeding a hydrothermally processed diet. Increase in FI and PR, adversely affect nutrient availability for poultry. The direct effects of processing variables on starch, fat and protein digestibility, Min bioavailability and retention as well as digestive dynamics of starch and protein appear to be largely confounded with indirect impact of HTP through FI increment. The hydrothermal treatments, particularly the HTST processes, seem to increase fiber solubility and digesta viscosity which could lead to a negative impact on nutrient digestibility. However, reduction of ANF by these processes can have a positive impact on nutrient digestibility. Therefore the final outcome of HTP in terms of nutrient digestibility, is principally dependent on feed formulation, chemical composition of the feed ingredients or/and final feed, presence and concentration of ANF as well as hygiene status of the feed.

This study was conducted to investigate the effects of phytase (Phy), benzoic acid (BA) and their interactions on growth performance, nutrients digestibility and tibia mineralization in broiler chickens fed standard or nutrient,s deficient diets. A total of 768 one-d-old male chicks were divided into 8 treatments for 42 d. The treatments were as follows:positive control (PC), PC diet with 0.5 g/kg of BA, PC diet with 500 FTU/kg of Phy, PC diet with 0.5 g/kg of BA and 500 FTU/kg of Phy, negative control diet (NC) with a nutrient deficiency (ND) equal to matrix value of 500 FTU/kg of Phy, NC diet with 0.5 g/kg of BA, NC diet with 500 FTU/kg of Phy, and NC diet with 0.5 g/kg of BA and 500 FTU/kg of Phy. Broiler chickens received NC diets had lower body weight gain (BWG), feed intake (FI) and higher feed conversion ratio (FCR) in the entire experiment (P ≤ 0.05). Dietary ND negatively influenced tibia and toe ash contents, serum, and tibia P contents as well as ileal P, Ca and CP digestibility at d 28 (P ≤ 0.05). FCR of d 1 to 11 and d 12 to 24 improved when Phy was added to NC rather than PC diets (P ≤ 0.05). Phy supplementation did not affect serum P and Ca content at d 28 (P> 0.05), but reduced serum alkaline phosphatase content in broiler chickens fed PC diets (P ≤ 0.05). Phy supplementation increased tibia and toe ash contents at d 28, especially in broiler chickens fed NC diets (P ≤ 0.05). Inclusion of BA did not influence (P> 0.05) tibia ash, tibia Ca and P contents at d 28, but increased toe ash content (P ≤ 0.05).The interaction between BA and the dietary nutrient level was significant for FCR of d 25–42 and d 1–42 (P ≤ 0.05). Broiler chickens fed PC diets with BA had better FCR compared with those fed PC diets without BA atd 25–42 (P ≤ 0.05). Adding Phy to the diets containing BA improved BWG and FI atd 1–11(P ≤ 0.05). In conclusion, Phy was effective in improving some growth performance traits, and bone mineralization especially when added to NC diets. However, BA had a positive effect on FCR of broiler chickens fed PC diets and had no impact on ileal nutrients digestibility, but improved toe ash content.

The present study evaluated the impacts of Bacillus subtilis (BAS) inclusion in broiler diets with standard nutrient content or nutrient deficiency (ND) on growth performance (GP) and nutrient digestibility. The 42 d experiment consisted of 6 experimental diets, a diet with standard nutrient content, and 2 diets with different levels of energy and protein deficiency, without or with BAS. At the end of experiment, apparent ileal digestibility coefficients (AIDC) of starch, crude protein (CP), and gross energy (GE) were determined. Furthermore, impacts of BAS supplementation in standard diets on gut histomorphology, bacterial metabolic activity, and composition were evaluated. Performance and AIDC data were subjected to ANOVA using GLM procedure with a 3 (nutrient levels) × 2 (BAS presence/absences) factorial arrangement of treatments. Gut histomorphology and microbiology data, obtained from broilers fed standard diets without (S) and with BAS (SB), were assessed by an independent Student's t-test. The ND in diets was effective enough to cause nutritional stress and negatively affect performance. Inclusion of BAS in both types of diet improved GP, which was due to the fact that adding BAS in these diets led to improvements in AIDC of CP, starch, and GE (P ≤ 0.05). Comparing only 2 experimental groups, S and SB, revealed no impact on bacterial composition and metabolism in the ileum and cecum, except a reduction in ileal lactobacilli number for SB group. Adding BAS to standard diet reduced crypt depth (CD) and increased villus length to CD ratio in the duodenum, whereas it had no impact on other histomorphological variables in the duodenum, jejunum, and ileum. In conclusion, supplementation of broiler diets with probiotic BAS can positively affect growth performance and nutrient digestibility and this positive impact might even be more pronounced in nutrient-deficient diets. However, the extent of the alleviating ability of BAS in nutrient-deficient diets as well as the biological mechanisms for such a phenomenon needs to be studied further.

Various milling methods result in different particle size distributions and, in combination with mash and thermal treatment (expandate) of the feed, may have an impact on nutrient digestibility, pH of the digesta and subsequently the performance of an animal. Since this aspect has not been widely considered in laying hens, the objective of the present study was to investigate the effects of milling method, expansion, and particle size of feed on performance, apparent ileal nutrient digestibility, and pH of digesta in laying hens. Twelve variants of the same diet were produced. Four different milling techniques (hammer mill, roller mill, disc mill, and wedge-shaped disc mill) were used to grind the feed cereals. Coarse feed was obtained from all four mills. Additionally, fine feed was obtained from the hammer mill and the roller mill. Each of the six feed variants was offered as mash or expandate, resulting in a total of 12 treatments. The duration of the experimental period was 21 days. A total of 576 layers, each 19 weeks of age, were used in eight replicates. The statistical analysis for the four milling methods and two thermal treatments was performed using a 4×2 factorial arrangement. The effect of particle size was investigated using a 2×2×2 factorial arrangement including the coarse and fine particle sizes that were produced with the hammer mill and the roller mill as well as the mash and expandate. The animal performance and the pH of the digesta were not affected by the treatments. Ileal digestibility of starch was significantly improved by feeding mash compared to expandate (P=0.013) and by feeding coarse compared to fine feed (P=0.028). Based on this study, the tested milling methods can be used for the production of feed for laying hens without affecting performance and digestibility of nutrients.