The Challenge: A Tough Bug Gets Tougher.

Authors: Dr. Laura Merriman, Dr. Spencer Becker, and Dr. Gustavo Cordero of AB Vista

It is widely understood that Enterotoxigenic Escherichia coli (ETEC) infections following weaning are a persistent and costly challenge faced by swine producers, even after decades of progress in nursery pig health programs. Historically, both F4 and F18 ETEC strains have been prevalent, but recent data from the Iowa State University Veterinary Diagnostic Lab shows that F18 has emerged as the dominant field strain (Paiva et al., 2024). At the same time, F18 ETEC susceptibility to conventional antimicrobial and immunologic interventions continues to decline, highlighting the need for alternative strategies to protect nursery pig health and performance. An integrated approach that combines management practices, targeted genetics, and novel nutritional strategies will be essential. For nutritionists, feeding a stimbiotic (Signis, AB Vista) offers a practical tool to reduce the negative impact of F18 ETEC in newly weaned pigs.

The Stimbiotic Concept: Jump-Starting Fiber Fermentation

First introduced in 2019, stimbiotics are defined as a new category of functional additives that promote the development of fibrolytic bacteria and fiber fermentation in the gut (González-Ortiz et al., 2019). Unlike prebiotics, which are added at high dosages (range of kilogram-per-tonne) and are intended to be completely fermented, stimbiotics are supplemented at a very low dosage (grams per tonne) and work to accelerate the maturation of a fiber-fermenting microbiome. This shift in the gut environment favors the production of beneficial short-chain fatty acids (SCFA; Cho et al., 2020; Figure 1) such as butyrate, a key fuel source for epithelial cells, ultimately improving intestinal integrity and resilience. Since their introduction into the market, stimbiotics have proven to be an effective nutritional strategy for supporting growth and efficiency, reducing mortality and medicinal interventions, and lowering the incidence of scours and ear necrosis in nursery pigs (Merriman et al., 2024). To further understand how Signis delivers these benefits under disease pressure, three controlled F18 challenge studies were conducted.

Figure 1. Effect of Signis on fecal short-chain fatty acid (SCFA) and branched-chain fatty acid (BCFA) concentration in nursery pigs raised in an unsanitary environment (Cho et al., 2020)

Trial 1: Chungbuk National University, Korea

The first study evaluated the effects of Signis supplementation in the presence and absence of an induced F18 ETEC challenge in corn-soy based diets (Song et al., 2022). Treatments were administered during the first three weeks in the nursery and pigs were challenged one-week post-weaning.

Key Findings:

• Growth Performance: Challenging the pigs resulted in a reduced body weight by 1.5 kg after 14 days (P < 0.05), indicating an effective F18 ETEC challenge. Signis led to an improved end body weight by 10%, daily gain by 24%, and feed efficiency by 18%, regardless of challenge (P < 0.05).
• Immune response: The F18 ETEC challenge increased total white blood cell (WBC) counts and neutrophil concentrations and decreased lymphocytes, indicating a systemic inflammatory response and immune stress. Signis supplementation modulated this immune response by lowering WBC and neutrophil levels (P < 0.05), and partially restoring lymphocyte counts (P < 0.10) compared to challenged controls.
• Inflammation: As expected, the F18 ETEC challenge elevated pro-inflammatory markers, including TNF-α, IL-6, and ileal calprotectin, indicating an inflammatory response. Supplementation with Signis blunted this response, significantly reducing levels of these markers (P < 0.06) and demonstrating that Signis attenuated the inflammation typically induced by an ETEC infection.
• Intestinal Morphology: Jejunal villus height and villus height-to-crypt depth ratio (VCR) were reduced by F18 ETEC challenge. Signis positively impacted villus height and VCR, with greater benefits in challenged animals (interaction; P < 0.05). These improvements indicate that Signis can help pigs maintain intestinal integrity and absorptive capacity during an F18 ETEC challenge.

Trial 2: Chungbuk National University, Korea

The second study investigating potential modes of action of Signis looked at the effects of Signis supplementation during the first two-and-a-half weeks in the nursery with or without an F18 E. coli challenge (Song et al., 2023). Pigs were fed a corn-soy based diet and challenged on day five post-weaning.

Key Findings:

• Growth Performance: Similar to the first study, the challenge reduced final pig body weight by 0.4 kg. In challenged animals, Signis resulted in an 8% improvement in body weight, a 32% increase in daily gain, a 6% increase in daily feed intake, and a 25% improvement in feed efficiency 12 days post-challenge.
• Intestinal Barrier Integrity: Supplementation of Signis in the challenged pigs improved apparent total tract digestibility of dry matter, crude protein, and gross energy in week two of the study (P < 0.05). The F18 ETEC challenge reduced the expression of the tight junction protein claudin-1 (P < 0.05), while Signis supplementation restored its levels in both non-challenged and challenged pigs.
• Blood Profile: Similar to Trial 1, the challenge increased WBC and neutrophils and decreased lymphocytes. F18 ETEC infection also resulted in elevated levels of pro-inflammatory cytokines TNF-α and IL-6. In challenged pigs, Signis supplementation increased lymphocyte concentration and reduced neutrophil levels on day 12 post-challenge (P < 0.01).

Trial 3: University of Arkansas, USA

The most recent study conducted evaluated Signis and the effects of different fiber sources in F18 ETEC-challenged pigs during the first three weeks post-weaning (Shirer et al., 2024; Becker et al., 2024; Shirer et al., 2025). Pigs were challenged on day 5 post-weaning. The dietary fiber sources tested were wheat middlings and a combination of sugar beet pulp and soy hulls.

Key Findings:

• Growth performance: Pigs fed wheat middlings with a stimbiotic ate more feed during the first 22 days post-weaning (P <0.05), resulting in a tendency for those pigs to have higher daily gain and body weight compared to pigs fed only wheat middlings (P <0.10). Pigs who were fed soy hulls and sugar beet pulp with or without a stimbiotic were intermediate.
• Fecal microbiome: On day 5 post-weaning, pigs fed Signis had an increased abundance of butyrate-producing bacteria Lachnospiraceae and Ruminococcaceae (P < 0.05). On day 0 and 7 post-challenge, piglets fed soy hulls and sugar beet pulp had increased abundance of Lachnospiraceae (P < 0.05). This demonstrates that Signis and fiber influence the presence of fibrolytic bacteria in the nursery phase, supporting the resilience of piglets facing an F18 ETEC challenge.
• Inflammation: Fecal calprotectin was measured as a marker of inflammation. Regardless of fiber type, Signis reduced calprotectin by 67% and 56% on day 7 and day 24 post-challenge, respectively, (Figure 2; P < 0.05) compared to pigs that did not receive Signis. This suggests that Signis aids in a faster recovery resulting in improved pig health.

Figure 2. Fecal calprotectin of nursery pigs challenged with F18 ETEC fed with or without a Signis on days 0, 7, and 24 post-infection (dpi).

Conclusion

Collectively, these three studies demonstrate that supplementing nursery diets with Signis meaningfully reduces performance losses, intestinal damage, and inflammation associated with F18 ETEC infections. These benefits translate into a more productive and resilient pig, an outcome that is increasingly valuable as F18 ETEC continues to be an issue in nursery barns and antimicrobial sensitivity decreases. While no single approach can replace proper management and biosecurity, Signis is a proven, low-dose additive that complements existing health programs and offers nutritionists a practical tool to mitigate F18 ETEC challenges and set weaned pigs up for success.