The pig's gastrointestinal tract (GIT) is critical in digesting food into absorbable nutrients required by the body for maintenance and production. In addition to digestive and absorptive functions, the pig's GIT is critical in maintaining immune homeostasis. Importantly, the intestine is the largest immune organ in the body, accounting for more than 70% of immune cells in the body.

There are many microorganisms in the intestine that contribute to mucosal immunity. The two interact with each other, and the latter regulates the distribution and composition of intestinal microorganisms and the homeostasis of the intestinal microbiota by secreting various immune effector factors; Gut microbes can also promote the differentiation of immune cells, including regulatory T cells, through their specific components or metabolites.

Therefore, a fully functional and healthy GIT is crucial to the production efficiency of pigs at all stages.

1. Healthy gastrointestinal tract

1 .Normal function of the stomach

The oral cavity is the beginning of the gastrointestinal tract. Its saliva contains epithelial growth factors, mucins and prostaglandins that protect the esophagus; at the same time, its electrolytes and water are also important for body temperature regulation and body homeostasis. effect.

The pH value of gastric juice and feed acidification play an important role in the defense mechanism of pathogenic microorganisms.

2. Healthy Small Intestine

The main site for digestion and absorption of macro- and micronutrients is the small intestine.

The first and shortest part of the small intestine is called the duodenum, which plays an important role in food digestion by receiving partially digested food from pancreatic and gastric secretions containing digestive enzymes. crucial role.

The jejunum accounts for nearly 80% of the pig small intestine. It has circular folds and villi to increase the surface area and absorb the small nutrient particles digested in the duodenum.

The ileum is responsible for the absorption of vitamin B12, the reabsorption of conjugated bile salts, and other nutrients not absorbed by the jejunum.

The main digestive enzymes are amylase (which breaks down starches and carbohydrates into sugars), lipase (which breaks down lipids (i.e. fats and oils) into glycerol and fatty acids), and proteases (which break down proteins into amino acids).

Trypsin and chymotrypsin are the two most important protein-digesting enzymes in the intestine: trypsin breaks down proteins into peptides by recognizing the peptide bonds formed by the carboxyl fragments of arginine and lysine; chymotrypsin Mainly degrades proteins and peptides into small peptides and amino acids.

3. Enteric nervous system (ENS)

The enteric nervous system (ENS) and its major components (myenteric and submucosal plexuses) regulate major intestinal processes in the intestine, Examples include detection of nutrients, immune responses, motility, microvascular circulation, intestinal barrier function, epithelial secretions of fluids and bioactive peptides.

ENS also works synergistically with intestinal microbiota to maintain a stable intestinal microenvironment. The intestinal mucus layer serves as the first line of defense against the penetration of pathogenic microorganisms into the circulation by forming a barrier between the intestinal epithelium and the luminal contents; this barrier also prevents commensal microbiota from interacting with the gut .

4. Healthy Large Intestine

The large intestine is a long, continuous tube in the digestive system that includes the cecum, colon, and rectum.

The pig's large intestine performs physiological tasks such as absorbing fluids and electrolytes (water, vitamins and minerals) and acting as a physical barrier against microbial invasion.

A healthy large intestine not only helps absorb nutrients but also helps eliminate toxins and waste from the body.

A beneficial microbial community indicates a healthy large intestine, and a healthy large intestine relies on a balanced microbiota or healthy microecosystem.

Microorganisms ferment endogenous secretions and undigested dietary components in the large intestine, mainly dietary fiber (DF), lipids and insoluble proteins; short-chain fatty acids (SCFA) and some vitamins can be fermented here A portion is absorbed, which helps provide nutrition to the pig.

2. Factors interfering with gastrointestinal health

The main problem with gastric function is insufficient acidity of gastric juice, which will impair protein digestion and removal of harmful microorganisms. This condition mainly occurs around weaning, when the glandular part of the stomach is still not fully functional.

The higher buffering capacity of high-protein feeds will reduce acidity.

Particle size. Roughage increases the mean residence time and improves the grading of stomach contents.

2. Small intestinal disorders

Intestinal oxidative stress (OS)

Intestinal exposure to foreign bodies and pathogens is a key source of reactive oxygen species (ROS). Excessive production of ROS can cause an imbalance in the antioxidant system of animals, leading to intestinal oxidative stress (OS).

Intestinal oxidative stress affects the early stages of intestinal damage and serves as an activator of intestinal barrier dysfunction, leading to immune imbalance and inflammation.

Weaning stress

Weaning and the following period are the most stressful events for pigs. They can cause intestinal and immune system dysfunction, leading to reduced health, growth and feed intake in pigs, especially in the first weeks after weaning.

The intestinal immune system is immature, making it highly susceptible to changes in intestinal morphology, inflammation, and intestinal epithelial permeability.

The intestinal morphology and histology of piglets are destroyed, and the length of the small intestine and the height of the villi are reduced; on the other hand, due to the loss of tight junction (TJ) proteins (zona occlusiveus protein-1 (ZO-1), occlusive protein) If it is loose, harmful substances (such as bacteria) can easily enter the bloodstream from the lumen.

Mycotoxins

Fumonisins produced by Fusarium spp., specifically fumonisin FB1 (FB1) and fumonisin, specifically deoxynivalenol ( DON), is the most damaging mycotoxin to the intestinal tract.

FB1 is produced by common pathogenic Fusarium and proliferating Fusarium species in corn. Ingestion of FB1 by piglets can cause villus fusion and atrophy, affecting intestinal absorption of nutrients; it can also lead to changes in cytokine profiles and antibody responses. of reduction.

DON produced primarily by Fusarium graminearum and Fusarium graminearum in wheat, barley, and corn causes toxic and immunotoxic effects in various cell systems.

Environmental Stress

Environmental factors such as temperature, management and pathogens all affect pig intestinal health: adverse environmental conditions, such as high ambient temperatures, exceed the thermal comfort of finishing pigs ( 15-25°C), impairing its ability to control internal temperature, leading to heat stress (HS). HS-induced intestinal hypoxia, inflammation, and OS can negatively affect intestinal integrity and function in pigs.

Pathogenic stressors

Intestinal disease is the result of pathogenic infection.

Intracellular Clostridium infects the small and large intestines and can cause porcine proliferative enteropathy (ileitis); it causes inflammation and thickening of the ileum and proximal colon, reducing nutrient absorption.

Stress-affected intestinal permeability can lead to the entry of pathogenic bacteria, leading to intestinal pathology and functional impairment, thereby reducing pig performance.