Understanding weaning stress through the gut: Ulia’s contribution to PIG-PARADIGM

As she wraps up her PhD, that combination of disciplines has shaped a research project that tackles one of the most persistent challenges in pig production: post-weaning diarrhea—and the role stress may play in it.

“Weaning is a natural process, but in the pig industry it’s done abruptly,” Ulia explains. “Piglets are separated from the sow, mixed with unfamiliar piglets, and introduced to a completely new diet.”

This transition happens at a vulnerable time. “The gastrointestinal tract of piglets is still not well developed,” she says. “So all of these stressors can contribute to the onset of post-weaning diarrhea.”

The condition is typically managed with antibiotics—but that solution comes with consequences.

“Because of extensive antibiotic use, it may lead to antimicrobial resistance,” Ulia notes. “Some people even describe it as a silent pandemic, both in animals and humans.”

Looking at stress as a biological Driver

Rather than focusing only on diet or pathogens, Ulia’s research takes a different approach: stress itself.

Her project is built around the microbiota–gut–brain axis, which she describes as “a complex bidirectional link between the brain and the gut involving the nervous system, the microbiome, its metabolic products, and also the immune system.”

“The question in my project is whether stress—specifically weaning stress—can increase susceptibility to diarrhea from this perspective,” she explains.

To answer this, she designed a PhD project consisting of three interconnected studies: one in vivo experiment with piglets and two in vitro experiments to isolate specific mechanisms.

In her main in vivo study, Ulia induced physiological stress in piglets using ACTH, a hormone that stimulates cortisol production.

“Cortisol is the major stress hormone in piglets,” she says. “So we used ACTH to mimic prolonged physiological stress.”

The results point in a clear—if concerning—direction.

“We observed that prolonged physiological stress marginally exacerbates susceptibility to diarrhea,” Ulia explains. “So it means stress can worsen the condition.”

While this may seem intuitive, the finding is important: it provides experimental evidence that stress is not just a welfare issue, but a biological factor influencing disease outcomes.

“That’s the point,” she adds. “We want to know whether stress has an effect, so that we can do something in relation to stress management.”

One of the most unexpected results from the study came from the microbiome analysis.

“Interestingly, we saw an increase in the relative abundance of Lactobacillus following prolonged stress exposure,” Ulia says.

This finding runs counter to much of the existing literature.

“Many studies suggest that we would see a decrease in Lactobacillus,” she explains. “So we didn’t expect this result.”

The implication is not yet clear.

“We still need future research to explore the mechanism,” she says. “We don’t know whether this increase contributes to stress resilience or whether it may exacerbate susceptibility to diarrhea. We cannot answer that yet.”

To better understand how stress affects the gut, Ulia complemented her in vivo study with two in vitro experiments.

One used intestinal epithelial cell models derived from piglets, while the other involved fermenting digesta samples in the lab to observe microbial responses under controlled conditions.

“In the in vitro fermentation, we tested the direct effect of cortisol on the microbiota,” she explains.

But here, the results told a different story.

“We did not see a big direct effect of cortisol on the microbiota profile,” Ulia says.

The reason, she suggests, lies in the complexity of the living system.

“In vivo, we have the immune system and the nervous system interacting,” she explains. “In vitro, we only have the microbiome. So we are missing the bigger mechanism.”

Learning across disciplines

Ulia’s work sits within an emerging research area. “The microbiota–gut–brain axis has been extensively studied in humans and rodents,” she says, “but it is still developing in livestock.”

This meant looking beyond traditional animal science.

“I had to learn from human studies as well,” she explains, highlighting how interdisciplinary the field has become.

As part of PIG-PARADIGM, she worked within a large international network of researchers. “We have five universities and more than 20 PhD students,” she says. “It gave me a lot of opportunities for networking and learning.” The project also allowed her to shape her own research direction.

“I was very lucky to have the flexibility to design my experiments,” Ulia reflects. “That experience is very valuable for my future career.”

As her PhD comes to a close, Ulia’s research contributes to a growing understanding of how stress interacts with gut health in piglets—and why it matters.

Her findings reinforce a key message: managing stress could be an important part of reducing disease and, ultimately, reliance on antibiotics.

At the same time, her work highlights just how complex the biology is.

“We still need more research to understand the mechanisms,” she says. “But this is a step toward understanding what happens when piglets are exposed to stress.”

In that sense, her project does more than answer a single question—it opens the door to new ones, helping to shape the future direction of research within PIG-PARADIGM and beyond.