Most individual fish in wild and farmed populations can be infected with parasites. Fish intestines can harbour protozoans, myxozoans and helminths, which include several species of digeneans, cestodes, nematodes and acanthocephalans. Enteric parasites often induce inflammation of the intestine; the pathogen provokes changes in the host physiology, which will be genetically selected for if they benefit the parasite. The host response to intestinal parasites involves neural, endocrine and immune systems and interaction among these systems is coordinated by hormones, chemokines, cytokines and neurotransmitters including peptides. Intestinal fish parasites have effects on the components of the enteric nervous and endocrine systems; mechanical/chemical changes impair the activity of these systems, including gut motility and digestion. Investigations on the role of the neuroendocrine system in response to fish intestinal parasites are very few. This paper provides immunohistochemical and ultrastructural data on effects of parasites on the enteric nervous system and the enteric endocrine system in several fish–parasite systems. Emphasis is on the occurrence of 21 molecules including cholecystokinin-8, neuropeptide Y, enkephalins, galanin, vasoactive intestinal peptide and serotonin in infected tissues.

Microbiome research in the last two decades has delivered as a key finding that the human intestine hosts a unique and complex ecosystem with many variables affecting the composition of the microbiota and in turn its function in metabolism and immune defence. Hundreds of external (environmental) factors have meanwhile been identified as significantly associated with bacterial biomass and diversity and, amongst these, diet is considered as a key determinant of microbial populations. However, dietary intervention studies, including those with fermentable substrates that have bulk effects on bowel functions, have revealed only very minor effects on overall microbiome composition and usually show only a very few species changing in population size. What that means in the context of hundreds of different species coexisting in competition or mutualism in the human colon is far from understood. This review addresses some of the current limits in research on diet effects by taking anatomical and physiological features of the intestine into consideration. It also provides some recommendations on future human studies needed to assess how the diet influences the microbiome and associated effects on metabolic health.

The aim of this study was to investigate the effect of dietary replacement of soya bean meal (SBM) with faba bean (FB) and a blend of non-starch polysaccharide (NSP) degrading enzymes on the gastrointestinal function, growth performance and welfare of young turkeys (1 to 56 days of age). An experiment with a 2×2 factorial design was performed to compare the efficacy of four diets: a SBM-based diet and a diet containing FB, with and without enzyme supplementation (C, FB, CE and FBE, respectively). In comparison with groups C, higher dry matter content and lower viscosity of the small intestinal digesta were noted in groups FB. The content of short-chain fatty acids (SCFAs) in the small intestinal digesta was higher in groups FB, but SCFA concentrations in the caecal digesta were comparable in groups C and FB. In comparison with control groups, similar BW gains, higher feed conversion ratio (FCR), higher dry matter content of excreta and milder symptoms of footpad dermatitis (FPD) were noted in groups FB. Enzyme supplementation increased the concentrations of acetate, butyrate and total SCFAs, but it did not increase the SCFA pool in the caecal digesta. The enzymatic preparation significantly improved FCR, reduced excreta hydration and the severity of FPD in turkeys. It can be concluded that in comparison with the SBM-based diet, the diet containing 30% of FB enables to achieve comparable BW gains accompanied by lower feed efficiency during the first 8 weeks of rearing. Non-starch polysaccharide-degrading enzymes can be used to improve the nutritional value of diets for young turkeys, but more desirable results of enzyme supplementation were noted in the SBM-based diet than in the FB-based diet.

A 4 × 2 factorial experiment was conducted to investigate the effect of a processed soy protein (PSP) on broiler performance and digestive physiology. Four inclusion levels of PSP (0, 25, 50 or 100 g/kg in either corn or wheat-based diets) were used in the starter diets. Feed intake was significantly lower (P < 0.01) on corn-based diets than those on wheat-based diets at 35 d. Over the first 10 d, chicks on corn-based diets tended (P < 0.09) to have higher body weight (BW) than wheat-based diet chicks. Across the 35 d trial, PSP level showed a strong tendency (P < 0.06) to be related to higher BW in birds, regardless of grain type. Both grain and PSP experimental factors significantly (P < 0.01, and P < 0.001) interacted at an early age, improving BW and feed conversion ratio (FCR) for birds received high PSP on wheat-based diets. Significantly heavier (P < 0.01) small intestine and gizzard + proventriculas weights at an early age, and heavier (P < 0.001) gizzard + proventriculas and pancreas during the grower stage were recorded in birds fed the corn-based diets. At 24 d, pancreatic chymotrypsin amidase and lipase enzymes were significantly (P < 0.01) more active in chickens fed the wheat-based diet. The interaction of PSP level and the type of the grain was significant (P < 0.01) for pancreatic chymotrypsin amidase and lipase as well as jejunal maltase (P < 0.05). Both experimental factors had a significant influence on jejunum histomorphology at 24 d of age (P < 0.001). There was a significant interaction between level of PSP and the type of grain (P < 0.05) resulting in the highest villus surface areas being seen for birds fed the corn-based diet and receiving the medium level of PSP. The trial demonstrated that PSP supplement can be included at between 50 and 100 g/kg of starter diets, depending on the basal diet.

We analysed the spatio-temporal sequence of events concerning the morphology, physiology and ecology of the gut of piglets during the 2 weeks following weaning, in order to provide a limited number of variables that could be relevant markers of the gut post-weaning changes. An experiment was conducted on sixty piglets fasted for 2 d, then administered a weaning diet with a moderate or a high content of wheat using controlled gastric feeding, and slaughtered at different time-points post-weaning. Sixty-nine variables were analysed by principal component analysis. The results showed that the temporal changes induced in the gut by weaning can be divided into two periods: an acute period happening immediately after weaning, followed after day 5 by a more progressive adaptative and maturational phase. The main factors of this adaptation were the refeeding process and the time, while the diet per se had little influence. The villus length, lactase activity, macromolecule fluxes across the jejunum and the plasma cholecystokinin were proposed as markers of the acute phase. The mass of the jejunum, the weight of the pancreas, the content of stomach, the trypsin activity and the theophylline-induced secretion in jejunum were related to the re-feeding. Markers proposed to follow the gut maturation were the maltase activity, the glucose absorption and the basal resistance in the ileum, the lactobacilli and enterococci in the colon, and the pH of colonic and caecal contents. These markers might be helpful to design suitable diets to limit post-weaning gut disorders in pigs.