According to Gram Research analysis, specific gut bacteria are strongly associated with whether mother pigs can get pregnant after weaning their piglets. A 2026 study of 85 pigs found that a harmful bacterium called Clostridia was 94.6% accurate at predicting which pigs would struggle to conceive, and this bacterium produces chemicals that disrupt the pig’s reproductive metabolism. Changing the balance of bacteria in a pig’s gut through diet or probiotics could potentially improve fertility, though this approach still needs testing.
Scientists discovered that the types of bacteria living in a pig’s gut are connected to whether a mother pig can get pregnant again after weaning her piglets. By studying the poop samples of 85 pigs, researchers found two different groups of bacteria that work against each other. Pigs that could get pregnant had more helpful bacteria that break down nutrients better, while pigs that couldn’t get pregnant had bacteria that produce different chemicals. This discovery could help farmers improve pig breeding by adjusting what bacteria live in the pig’s gut through diet or other treatments.
Key Statistics
A 2026 study of 85 pigs published in Animal Microbiome found that a computer model based on 48 bacterial strains could predict which pigs would fail to get pregnant after weaning with 94.6% accuracy in the original group and 81.8% accuracy in a validation group of 29 pigs.
Researchers identified that pigs unable to conceive after weaning had significantly higher ratios of secondary to primary bile acids in their feces, a metabolic change driven primarily by a single Clostridia bacterial strain that was enriched in non-fertile pigs.
Among 608 estrus-associated bacterial strains identified in the study, Guild 1 bacteria—more common in fertile pigs—contained more genes for nutrient breakdown and folate production but fewer antibiotic resistance and disease-causing genes compared to Guild 2 bacteria found in non-fertile pigs.
The Quick Take
- What they studied: Whether the bacteria in a pig’s digestive system affect whether mother pigs can get pregnant again after weaning their babies
- Who participated: 85 pigs total, with 29 pigs used to test the findings. The pigs were divided into two groups: those that got pregnant after weaning (normal) and those that didn’t (non-return)
- Key finding: A specific strain of bacteria called Clostridia was much more common in pigs that couldn’t get pregnant, and this bacteria produces chemicals that change how the pig’s body processes bile acids, which are important for reproduction
- What it means for you: Farmers might be able to help pigs get pregnant again faster by changing their diet or using probiotics to shift the balance of bacteria in their gut, though more testing is needed before this becomes a standard practice
The Research Details
Researchers collected poop samples from 85 pigs and used advanced DNA technology to identify all the different bacteria living in their guts. They looked at the genetic material from these bacteria to understand what jobs each type of bacteria does in the pig’s body. They also measured the chemicals in the poop to see how the bacteria were affecting the pig’s metabolism. Finally, they created a computer model that could predict whether a pig would get pregnant again just by looking at which bacteria were present in its gut.
The scientists divided the bacteria into two competing groups or “guilds.” Guild 1 bacteria were more common in pigs that got pregnant normally, while Guild 2 bacteria were more common in pigs that didn’t get pregnant. They tested their computer model on a separate group of 29 pigs to make sure it actually worked.
This research approach is important because it goes beyond just identifying which bacteria are present—it shows exactly which genes these bacteria have and what chemicals they produce. This level of detail helps scientists understand the actual mechanism of how bacteria affect pig fertility, not just that they’re connected. By understanding the specific bacteria and genes involved, farmers could potentially target these bacteria with specific treatments rather than using general antibiotics or probiotics that might not work as well.
The study used advanced DNA sequencing technology that can identify bacteria at a very detailed level. The researchers validated their computer model on a separate group of pigs, which is important because it shows the findings aren’t just a lucky coincidence with the first group. However, the validation group was relatively small (29 pigs), so larger studies would strengthen the findings. The study focused on one specific farm population, so results might vary in different pig breeds or environments.
What the Results Show
The researchers identified 608 different bacterial strains associated with whether pigs got pregnant after weaning. When they focused on the 48 highest-quality bacterial strains and created a computer model, it could correctly identify which pigs would get pregnant 94.6% of the time in the original group and 81.8% of the time in the validation group. This is considered excellent performance for a prediction model.
The two competing bacterial guilds had very different characteristics. Guild 1, which was more common in pigs that got pregnant normally, had more genes for breaking down plant material and making folate (a B vitamin important for reproduction). Guild 1 also had fewer genes that help bacteria resist antibiotics and cause disease. Guild 2, which was more common in pigs that couldn’t get pregnant, had the opposite pattern—more antibiotic resistance genes and disease-causing genes, but fewer helpful nutrient-processing genes.
The most important finding was about bile acids, which are chemicals the body makes to help digest fats. In pigs that couldn’t get pregnant, the bacteria were converting primary bile acids (the type the body makes) into secondary bile acids (a different form) at much higher rates. A specific bacterium called Clostridia strain SFHK01 was responsible for much of this conversion, and this bacterium was much more abundant in pigs that couldn’t get pregnant.
The researchers created a simple scoring system based on the ratio of the two bacterial guilds, called the Guild Microbial Index (GMI). This simpler measure could also predict pregnancy status with reasonable accuracy (81.8% correct), suggesting that farmers might not need expensive DNA testing—they could potentially use simpler measurements to predict fertility problems. The study also showed that the specific secondary bile acids accumulating in non-pregnant pigs were different from those in normal pigs, suggesting that the type of bacterial conversion matters, not just the amount.
Previous research has shown that gut bacteria affect reproduction in other animals, including humans and mice, but this is one of the first studies to identify the specific bacterial strains and genes involved in pig fertility. Earlier studies suggested that bacteria affect reproduction through nutrient absorption and hormone metabolism, and this research confirms that mechanism while adding the new finding about bile acid metabolism. The level of detail achieved here—identifying specific bacterial strains and their genes—is more advanced than most previous animal reproduction studies.
The study was conducted on pigs from a single farm, so the results might not apply to all pig breeds or farming conditions. The validation group was relatively small (29 pigs), which means the 81.8% accuracy rate could change with larger studies. The research is observational, meaning it shows which bacteria are associated with fertility problems but doesn’t prove that changing the bacteria will fix the problem—that would require intervention studies. The study doesn’t explain why these specific bacteria cause fertility problems, only that they’re connected. Finally, the research was done in pigs, so results may not directly apply to other animals or humans.
The Bottom Line
Based on this research, farmers might consider dietary interventions that promote Guild 1 bacteria and reduce Guild 2 bacteria, though this remains experimental. Potential approaches could include adjusting fiber types in feed, using specific probiotics, or modifying feed additives—but these would need to be tested in controlled studies first. The current evidence is strong enough to warrant further research but not yet strong enough to recommend as a standard farming practice. Confidence level: Moderate—the research is well-designed but needs validation in larger, multi-farm studies.
This research is most relevant to pig farmers and veterinarians working with breeding sows who are experiencing delayed pregnancy after weaning. It may also interest animal nutrition scientists and microbiome researchers. This research is not directly applicable to humans or other animal species at this time, though it may inspire similar research in other animals. Farmers with small breeding operations might not have access to the DNA testing required, though simpler measurement methods are being developed.
If dietary or probiotic interventions based on this research are developed and tested, farmers might see improvements in pregnancy rates within one to two breeding cycles (roughly 3-6 months). However, this is speculative—the current research only identifies the bacterial problem, not the solution. Any actual intervention would need to be tested in controlled studies before farmers could expect reliable results.
Frequently Asked Questions
Can changing a pig’s diet fix fertility problems caused by bad gut bacteria?
Research shows specific bacteria are linked to pig fertility problems, but scientists haven’t yet proven that changing diet fixes the issue. This study identifies the bacterial problem; the next step is testing whether dietary changes actually improve pregnancy rates in real farming conditions.
What is the connection between gut bacteria and getting pregnant in animals?
Gut bacteria affect how animals absorb nutrients and produce hormones needed for reproduction. This study found that certain bacteria change bile acid metabolism, which appears to disrupt the reproductive system. Different bacteria produce different chemicals that either support or interfere with fertility.
How accurate is testing gut bacteria to predict pig fertility problems?
A computer model based on 48 bacterial strains was 94.6% accurate at predicting fertility in the original study group and 81.8% accurate in a separate validation group of 29 pigs. However, larger studies are needed to confirm these accuracy rates work consistently across different farms and pig breeds.
Could this research about pig bacteria apply to human fertility?
While gut bacteria affect human reproduction too, this study was conducted only in pigs. The specific bacteria and mechanisms involved may differ significantly in humans. Separate research would be needed to determine if similar bacterial interventions could help human fertility.
What is the Clostridia bacteria doing that causes fertility problems?
Clostridia bacteria produce an enzyme that converts bile acids into different forms. These altered bile acids accumulate in the pig’s system and appear to disrupt hormones and metabolism needed for reproduction. The exact mechanism of how this affects fertility still needs further investigation.
Want to Apply This Research?
- Track sow fertility metrics including days from weaning to estrus return, pregnancy confirmation rates, and litter size. Compare these metrics before and after any dietary or probiotic interventions targeting gut bacteria.
- Implement a feed modification protocol designed to promote beneficial bacteria (Guild 1) in breeding sows’ diets. This could include adjusting fiber sources, adding specific prebiotics, or introducing targeted probiotics. Monitor individual sow response through estrus return timing.
- Establish a baseline measurement of each sow’s fertility performance and bacterial profile (if testing is available). After implementing any intervention, track estrus return timing weekly and pregnancy rates per cycle. Adjust interventions based on whether fertility metrics improve over 2-3 breeding cycles.
This research identifies associations between gut bacteria and pig fertility but does not yet prove that changing bacteria will improve fertility. Farmers should not make changes to breeding programs or animal care based solely on this study. Any dietary or probiotic interventions should be discussed with a veterinarian and validated through controlled testing on individual farms. This research applies specifically to pigs and should not be assumed to apply to other animals or humans. Results may vary based on pig breed, farm conditions, and management practices.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.