Improving Animal Welfare: UC Davis Researcher Tracks Rising Health Challenge in Swine
At the UC Davis Weill School of Veterinary Medicine, research often begins with a simple question: what problem in animal health still doesn’t have answers? For fourth-year veterinary student Kimberly Aguirre Siliezar, who is focusing on livestock medicine, that question led her deep into an emerging issue in the swine industry—pelvic organ prolapse (POP) in sows—and her research that hopes to help producers by anticipating high risk periods and improve herd sustainability.
Pelvic organ prolapse is a condition in which reproductive or internal organs protrude from the body, has become an increasing concern in swine production. For producers, POP in sows represents a serious welfare and economic challenge—often leading to sow loss, emergency interventions, and disruptions in herd productivity. Understanding when and why it occurs can help producers better anticipate high-risk periods and make management decisions that improve animal welfare.
While it has long been recognized, Aguirre Siliezar was struck by how much remains unknown about POP—especially in North America. “We’ve seen reports that sow mortality is rising, and POP is one of the contributors,” she explained. “But we still don’t fully understand why it’s happening or how to prevent it.”
That knowledge gap was one motivation for her involvement in the project, along with the opportunity to work alongside her mentor, Dr. Beatriz Martinez Lopez, professor in the Department of Medicine and Epidemiology and director of the UC Davis Center for Animal Disease Modeling and Surveillance (CADMS).
As principal investigator of the study, Martínez López led the research team studying the prevalence and risk factors associated with pelvic organ prolapse in sows. An expert in epidemiology, her research focuses on developing and applying tools that support more cost-effective, risk-based disease surveillance and control strategies.
According to Martínez López, the project grew out of conversations with swine producers who were increasingly concerned about rising cases of POP in their herds. Although producers recognized the condition was becoming more common, little information existed on its true prevalence or the factors contributing to it.
"Producers were telling us they were seeing more cases of pelvic organ prolapse, but there was very little data to show how common the problem actually was across the industry," Martínez López said. "We knew it was likely a multifactorial issue, but there was a real need to better understand the risk factors and identify management strategies that could help reduce its occurrence."
Just as importantly, working with CADMS gave Aguirre Siliezar access to the kind of large, collaborative research project she had hoped to be part of—one that combined academic knowledge with industry data to tackle real-world animal health challenges.
“That center is really amazing because they do a lot of international collaborations that look at animal populations and really important diseases in different countries,” Aguirre Siliezar said. “I’ve always been more interested in infectious diseases,” she said. “But this was an opportunity to work with a large dataset and collaborate with industry. It definitely pushed me out of my comfort zone.”
Indeed, what made her research especially compelling was the scale of the data. Working with researchers at CADMS and industry partner Pig Improvement Company (PIC), Aguirre Siliezar analyzed data from more than 100 farms with tens of thousands of pigs across the United States and Canada. “A lot of previous research has been smaller scale or conducted in other countries,” she said. “This dataset gave us a unique opportunity to look at large-scale trends across North America.”
Her study focused on identifying spatial and temporal patterns—essentially asking where and when POP occurs most frequently. The results confirmed what earlier literature had suggested: the incidence of POP is increasing over time. Between 2019 and 2024, the data showed a clear upward trend, with only a brief dip that the authors of the research suspected may be linked to COVID-related changes in farm management or monitoring.
But one of the most practical insights came from examining seasonal patterns. POP cases were more common during colder months—peaking in late fall and winter before declining in spring and summer. That finding offers producers something tangible: the ability to anticipate higher-risk periods and adjust monitoring and care accordingly.
“If producers know there’s a seasonal trend, they can increase surveillance during those months,” Aguirre Siliezar noted. “That means catching cases earlier and improving outcomes for the animals.”
Geographically, the story was different. Rather than being concentrated in a specific region, POP appeared to be increasing broadly across nearly all states included in the dataset. That suggests the issue is not tied to one climate, management style, or location—but may instead reflect industry-wide factors such as genetics or nutrition.
Aguirre Siliezar also explored environmental, or “climatic,” factors—such as temperature and soil moisture—to see whether they might correlate with POP incidence. While most variables were not strongly associated, one stood out: soil moisture. Decreases in soil moisture levels appeared to coincide with increased POP cases, particularly during dry seasons.
That finding opens the door to new thoughts of why POP is increasing. One possibility involves mycotoxins—naturally occurring toxins produced by fungi that can grow on feed crops like corn. The authors of the research study discussed how soil moisture may promote fungal growth on crops and lead to mycotoxin contamination in feed, a process that can have a delayed effect on overall sow health. Additionally, even indoor-housed sows may be exposed to dust via foot traffic, equipment, or ventilation, which can contribute to respiratory stress or coughing. Aguirre Siliezar said that “although these mechanisms are speculations, they provide a plausible explanation for these associations while also highlighting the need for further research on direct effects of feed quality and housing sanitation practices on POP incidence.”
“This study helps confirm trends and narrow our focus,” Aguirre Siliezar said. “It suggests that while environmental factors might play a role, we really need more detailed, farm-level and individual animal data to understand what’s driving POP.”
“We’re missing key information on both individual animal and farm-level factors that are critical to understanding this condition,” said Martínez López. “I totally believe pelvic organ prolapse is a multifactorial issue involving genetics, nutrition, management practices, and possibly comorbidities. The challenge is that all of these factors are interconnected. If we can better understand that complexity, we can start to develop more targeted recommendations for individual farms.”
That next step—partnering more closely with producers to gather detailed information on nutrition, health history, and management practices—will be critical. It also underscores a key principle of sustainable livestock production: collaboration. By working together, researchers and producers can identify risk factors earlier and improve animal welfare.
For Aguirre Siliezar, the project reflects a broader vision of veterinary medicine, one that connects hands-on care with research-driven prevention. “I want to be able to treat animals when they need it,” she said, “but also contribute to research that helps prevent those problems in the first place.”
The consequences extend beyond animal health and welfare. Sows that experience prolapse are often removed from herds, leading to economic losses for producers. In many cases, the condition is difficult to treat and likely to recur. Despite the challenges, the experience gave Aguirre Siliezar a new appreciation for the complexity of livestock health—and the role research can play in solving real-world problems.
“Being able to work with industry and use data to answer questions that producers actually have—that was really meaningful,” she said.
And for Martínez López, the project also provided an opportunity to reconnect with an industry she has been passionate about since growing up in Spain. Before building her career as an epidemiologist, she worked closely with swine production systems and developed an appreciation for the industry's culture of working together to solve challenges.
"I've always enjoyed working with the swine industry," Martínez López said. "The swine industry is a great one because they have a lot of data and a strong culture of collaboration. In the U.S., the National Pork Board, is a body that unifies most of the commercial systems and it's very easy to work with. Producers, researchers and industry organizations are often all looking in the same direction and working toward the same goals."