Everyone knows stress isn’t good. But did you know how complex the impact of stress is on the gut of the pig? When stress occurs, changes take place in the gut microbiota, physiology and mucosal immune function. The result is often diarrhea and a perfect environment for pathogens like E.coli to flourish, says Mike Tokach, professor at Kansas State University.
“A healthy intestinal barrier with low gut permeability is the key to minimizing diarrhea and pathogen proliferation,” Tokach says.
That’s why understanding the gut mucosal defenses can illustrate its importance in reducing post-weaning diarrhea, he adds.
How the Gut Defends Against Pathogens
Two mucosal layers are key to protect the epithelium of the gut. The outer mucosal layer is highly colonized by microbiota. In a healthy situation, microbiota are quite diverse and keep pathogenic bacteria at low levels though competition, Tokach shared at the recent American Association of Swine Veterinarians annual meeting. Secretory IgA also helps bind pathogenic bacteria to reduce colonization.
“The inner mucous layer is thought of as the ‘killing zone.’ It is a dense, highly cross-linked layer that, when intact, is impenetrable and prevents bacterial colonization because of a high concentration of antimicrobial peptides and secretory IgA,” he adds. “Maintaining a healthy inner mucous layer is one of the keys to preventing pathogenic diarrhea.”
In a healthy pig, goblet cells on the intestinal mucosa secrete mucous and mucins that form these inner and outer layers of defense. Epithelial cells also secrete mucins that help populate the kill zone. When stress sets in, these protectors up their efforts to increase defense to pathogens.
Tokach points out that tight junctions between individual cells further prevent pathogens that reach the mucosal surface from penetration.
“When this system breaks down, mucosal layers are thinned and lose the ability to prevent pathogens from attacking the mucosal surface. Coupled with breakdown of tight junctions, this leads to acute inflammation and diarrhea and, eventually, immunosuppression,” he says.
Why Young Pig Development is Key
The gut undergoes tremendous changes during the young pig’s life. Prior to weaning, villi and microvilli are elongated to maximize surface area for digestive capability. At weaning, villi are sloughed, and crypt depth increased greatly reducing the digestive capacity of the pig, he adds.
“The anorexia that often accompanies weaning of young pigs, especially with modern genetics selected for late maturity, contributes to the loss of villi and absorptive capabilities, increasing the potential for gut dysbiosis,” he says. Dysbiosis is the imbalance in the gut microbial community that is associated with disease.
Development of this normal gut barrier takes time. For example, in nature, it occurs at 12 to 14 weeks of age. In modern swine production, however, pigs are weaned at 3 to 4 weeks of age, which compromises gastrointestinal barrier development.
“Fantastic research by Adam Moeser at Michigan State University has demonstrated that gut permeability is much greater for pigs that have been weaned than pigs remaining on the sow and age at weaning has a profound impact on how the pig responds to weaning stress. As weaning age is increased from less than 21 days to 28 days, integrity of tight junctions increases linearly and gut permeability decreases. This means that pigs weaned at older ages can handle stressors with less negative impact than pigs weaned at younger ages,” Tokach says.
Research shows the important interaction between gut development and pathogenic responses. Pigs weaned at older ages can handle the intestinal challenges more easily than pigs weaned at younger ages.
“If you don’t challenge the pigs weaned at young ages, they do quite well with excellent growth, but disease challenges and other stress allow the increased gut permeability to become a problem and results in increased death loss,” he points out.
The K-State Applied Swine Nutrition team that contributed to his presentation also include Jordan Gebhardt, Jason Woodworth, Joel DeRouchey and Bob Goodband.
Read More:
When Stress Stacks Up: It’s Time to Make Weaning a Better Experience
8 Ways to Minimize Weaning Stress in Pigs
