How Gut Bacteria Can Improve Swine Production Back »

Written by Jamie L. Ortman under the direction and review of Rosie Nold.

Microbiology may not be what comes to mind initially when you think about swine production practices, but recent research may hold the key to making changes based on the veterinary feed directive regulations (effective January 1, 2017). Bacterial populations located all along the gastrointestinal tract of animals, collectively referred to as the microbiome, play an integrative, symbiotic role with their swine hosts. Researchers have uncovered some clear data that demonstrates beneficial effects on several factors of swine production, including increased feed:gain ratio, growth performance, and decreased pathogen load. The production effects are primarily attributed to reducing post-weaning stress and altering the microbiome with non-traditional feed additives.

Bacterial Infections & Post-Weaning Stress

Bacterial infections associated with post-weaning stress have been a problem for producers for decades. Over time, producers have developed strategies required to minimize these effects, such as phase feeding regimens, high quality feedstuffs, antibiotics, and different management practices. These strategies are used to help nursery pigs, which have an underdeveloped immune response and a highly fluctuating microbiota, adapt to their new feeding situations. Some of the more prominent methods used to treat diarrhea and/or improve feed efficiency are manipulation of the microbiome. It is likely that the previously used practice of feeding sub-therapeutic levels of antibiotics altered the microbiome specifically for piglets in highly stressful times, such as weaning and transitioning to solid feed. It has been speculated that the microbiome uses several mechanisms to reduce infections and improve growth performance in stressed piglets. Some of these are increasing diversity, earlier establishment of a beneficial “core” bacteria, and earlier immune regulation (Cammarota, Ianiro, Bibbo, & Gasbarrini, 2014).

Microbiome Management Benefits

Benefits reported are likely due to a shift in the proportion of different types of bacteria within the gut versus an actual population change. Researchers have reported that the addition of spent cider yeast significantly changed the piglets’ microbiota by reducing high levels of pathogenic bacteria while encouraging the growth of more beneficial bacterial populations. The addition of cider yeast reduced pathogenic enterobacteria, such as Salmonella and Escherichia spp. (Upadrasta et al., 2013). In an alternate study, researchers reported that the addition of certain probiotic species increased feed intake and improved growth performance. The author did not note any changes to the gut microbiome composition; however he did see a decline in a specific family of bacteria within the treatment group as compared to the control group (Cousin et al., 2012). Altering the microbiome is not only beneficial in stressed weanling piglets; it can also be helpful as an alternative to the increased antibiotic regulations.

Due to veterinary feed directive regulations, the concerns for finding alternatives to antibiotics has increased in priority. One such alternative that could be used is increased manipulation of the microbiome via the addition of probiotics and/or unconventional ingredients that alter the bacterial populations to increase diversity and immune modification. For example, Lactobacillus casei’s addition to the diet has been identified to reduce inflammation, decrease pH, and increase the IgA antibodies, indicating an increased immune response within the gastrointestinal tract of pigs (Galdeano & Perdigon, 2006). The immune response can reduce the likelihood of infection within the gut which can result in an increased growth until market weight.

Fermented Feeds

Fermented feeds are another possibility for improving performance. A study published in 2001, reported that 10-week-old pigs fed fermented feed had reduced numbers of pathogenic bacteria along the gastrointestinal tract (van Winsen et al., 2001). These results could be due to the increase in lactic acid producing bacteria found in the stomach of the treatment group animals. Therefore, a reduction in pathogens along the gut, via decreased pH and competitive exclusion, results in increased growth performance of the pigs. In a similar study, pigs fed fermented poultry by-products saw an increased feed:gain ratio, increased carcass weight, and a decrease in Enterobacteriaceae, Enterococci, Lactobacilli, and Salmonella (Urlings et al., 1993). The author speculates that the fermented diet encouraged bacterial shift within the gut and reduced diarrhea which allowed for an increased growth performance in the treatment group pigs (Urlings et al., 1993). Therefore, the use of fermented feeds could decrease pathogenic bacteria by altering the microbiome of the gastrointestinal tract which could lead to increased health benefits for the pigs and increased growth performance and profit for the producers.

The Bottom Line

Microbiology, in conjunction with nutrition, has the potential to be influential in the lives of producers and the individual pig. With increased potential to actively shift the microbiota, producers can obtain the benefits of increased growth performance, decreased infection rate and duration, and a reduction in antibiotic usage. Benefits have been observed within stressed weanling pigs and in infectious cases as a possible replacement for antibiotics. Ultimately, the study of the microbiome is only getting started as it slowly uncovers which species colonize the gut and what their function may be in regards to the pig. At the end of the day, microbiology has the potential to influence production rates and decrease production losses via shifts in the microbiome.


  • Cammarota, G., Ianiro, G., Bibbo, S., & Gasbarrini, A. (2014). Gut microbiota modulation: probiotics, antibiotics or fecal microbiota transplantation? Intern Emerg Med, 9(4), 365-373. doi:10.1007/s11739-014-1069-4
  • Cousin, F. J., Foligne, B., Deutsch, S. M., Massart, S., Parayre, S., Le Loir, Y., Jan, G. (2012). Assessment of the probiotic potential of a dairy product fermented by Propionibacterium freudenreichii in piglets. J Agric Food Chem, 60(32), 7917-7927. doi:10.1021/jf302245m
  • Galdeano, C. M., & Perdigon, G. (2006). The probiotic bacterium Lactobacillus casei induces activation of the gut mucosal immune system through innate immunity. Clin Vaccine Immunol, 13(2), 219-226. doi:10.1128/CVI.13.2.219-226.2006
  • Upadrasta, A., O'Sullivan, L., O'Sullivan, O., Sexton, N., Lawlor, P. G., Hill, C., Ross, R. P. (2013). The effect of dietary supplementation with spent cider yeast on the Swine distal gut microbiome. PLoS One, 8(10), e75714. doi:10.1371/journal.pone.0075714
  • Urlings, H. A. P., Mug, A. J., van ‘t Klooster, A. T., Bijker, P. G. H., van Logtestijn, J. G., & van Gils, L. G. M. (1993). Microbial and nutritional aspects of feeding fermented feed (poultry by‐products) to pigs. Veterinary Quarterly, 15(4), 146-151. doi:10.1080/01652176.1993.9694394
  • van Winsen, R. L., Urlings, B. A., Lipman, L. J., Snijders, J. M., Keuzenkamp, D., Verheijden, J. H., & van Knapen, F. (2001). Effect of fermented feed on the microbial population of the gastrointestinal tracts of pigs. Appl Environ Microbiol, 67(7), 3071-3076. doi:10.1128/aem.67.7.3071-3076.2001
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