There are a large number of microorganisms in the porcine intestinal tract. These microorganisms and their metabolites contribute to intestinal mucosal immunity, which is of great importance to the health of the host. The host immune system can regulate the distribution and composition of intestinal microorganisms and regulate the homeostasis of intestinal flora by secreting a variety of immune effector factors, such as mucin, secretory immunoglobulin A (sIgA), regenerating islet-derived III (RegIII)γ, and defensin. Conversely, intestinal microorganisms can also promote the differentiation of immune cells including regulatory T cells (Treg) and Th17 cells through their specific components or metabolites. Studies have shown that imbalances in the intestinal flora can lead to bacterial translocation and compromised intestinal barrier function, affecting the health of the body. This review focuses on the composition of the pig intestinal flora and the characteristics of intestinal mucosal immunity, discusses the interaction mechanism between the flora and intestinal mucosal immunity, as well as the regulation through fecal microbiota transplantation (FMT), dietary nutritional composition, probiotics and prebiotics of pig intestinal microecology. Finally, this review provides insights into the relationship between intestinal microorganisms and the mucosal immune system.

Large-scale pigeon farming in China is gradually increasing. However, studies on the basic nutritional requirements of breeding pigeons during lactation, which greatly influence the productivity and economic benefits of pigeon breeding, remain scanty. The objective of this study was to determine the optimal dietary energy/protein ratio requirements for lactating pigeons in summer. A total of 576 pairs of Mimas breeding pigeons were randomly divided into 12 groups (n = 48 per treatment), and each pair bred 4 squabs. A two-way ANOVA design with different protein levels (15%, 16%, 17%, and 18%) for factor A and different energy levels (12.6 MJ/kg, 12.8 MJ/kg, and 13.0 MJ/kg) for factor B was used to design 12 groups of experimental diets for feeding. The experiment lasted for 28 d. We found that ME level had little effect on breeding pigeons, but the CP level and dietary energy/protein ratio significantly affected the reproductive and growth performance of the pigeons. The lowest total weight loss (P < 0.01), and the highest egg production (P < 0.01) were observed in group 11 (18% CP, 12.8 MJ/kg). It had no effect on egg quality. Both ME and CP levels significantly affected the growth performance, slaughter performance and meat quality of squabs, and there was a strong interaction between CP and ME. The fastest growth rate (P < 0.01) was observed in group 11 (18% CP, 12.8 MJ/kg). The best CP and ME combination for the eviscerated weight, pectoral muscle weight, organ weight, 45 min meat color (L^⁎, a^⁎, b^⁎), pH, and muscle fiber characteristics were also group 11. Finally, the regression model revealed that the best dietary energy/protein ratio was 17.92 to 19.02 kcal/g for squabs and 16.72 kcal/g for the breeding pigeons. There was a strong interaction between energy and protein levels in breeding pigeons during the lactation period, and the best production performance was at 18% CP 12.8 MJ/kg. And this is recommended to be applied as the energy/protein ratio dietary requirement for breeding pigeons during lactation in the summer “2 + 4” pattern.

The nutritional requirements of breeding pigeons depend on their physiological period, breeding pattern, and environmental conditions. Despite works on reduced litter size in winter production to combat high mortality and the poor welfare of squabs, there are few studies on the related nutritional requirements of these pigeons. A total of 432 pairs of European Mimas pigeons were randomly divided into 9 groups in which 3 crude protein (CP) levels (15, 16.5, and 18%) and 3 metabolizable energy (ME) levels (12.2 MJ/kg, 12.4 MJ/kg, and 12.6 MJ/kg) were tested to determine the optimal energy and protein requirements of breeding pigeons in the winter "2 + 3" breeding pattern. The results showed that ME and CP levels had little effect on the body weight, feed intake, and egg quality of breeding pigeons during the lactation period. An 18% CP diet significantly increased the laying rate and hatchability (P < 0.05), but there was no difference in the laying rate with 18% CP and 16.5% CP during the whole reproductive cycle (P > 0.05). There was a significant interaction between ME and CP levels, and the laying interval of breeding pigeons in group 9 (18% CP; 12.6 MJ/kg) was significantly shortened (P < 0.05). For squabs, the ME level had no effect on growth performance, slaughter performance, or meat quality. The body weight of 21-day-old squabs in the 18% CP group increased by 3.16% compared with that of the 15% CP group, but there was no difference between the 18% CP and 16.5% CP groups. Compared with other experimental groups, group 7 (18% CP; 12.2 MJ/kg) had the fastest growth rate in squabs (P < 0.05), and the corresponding slaughter weight was also the heaviest (P < 0.05). We further found that the height of the squab intestinal epithelium was significantly increased in both the 16.5% CP and 18% CP groups of squabs (P < 0.01), but male breeding pigeons showed a certain degree of oxidative stress with an increase in CP level. In conclusion, the effects of 15 to 18% CP levels and 12.2 to 12.6 MJ/kg ME levels on the reproductive metabolism of breeding pigeons and the growth and development of squabs in the "2 + 3" breeding pattern during winter are small. For economic efficiency, we suggest that the CP level can be reduced to 16.5% while the ME level should not be less than 12.2 MJ/kg in practical production.

The present research examined the impact of L-glutamic acid (Glu) supplementation on the growth performance, muscle composition, gene expression correlated with muscle growth, and intestinal health of largemouth bass. There were 525 fish in total, which were distributed randomly into five groups. Each group had three replicates, and each replicate consisted of 35 fish. Groups with control and experimental diets were assigned glutamic acid amounts of 0.2%, 0.4%, 0.6%, and 0.8%. The findings demonstrated that glutamic acid supplementation enhanced growth performance, feed intake (FI), and condition factor (CF), with the best value being attained at 0.4% Glu. The mean muscle fiber area was increased and the muscle fiber density was decreased in the 0.6% Glu group. The levels of total amino acids and specific amino acids, such as glutamic acid, aspartic acid, leucine, valine, alanine, and glycine, were shown to be higher in the 0.6% Glu group. In the 0.6% Glu group, the mRNA expression levels of atrogin-1, murf-1, foxo3a, and 4e-bp1 were decreased compared to the control group. Conversely, the mRNA expression levels of myf5, myog, myod, s6k1, tor, akt, and pi3k were increased in the 0.6% Glu group compared to the control group. The 0.4% Glu group had higher intestinal amylase, lipase, and protease activities and greater villus height, villus width, and muscle thickness. In summary, Glu can support largemouth bass growth, muscular development, intestinal digestion, and absorption.