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Son et al. Microbiome Res Rep. 2025;4:29 https://dx.doi.org/10.20517/mrr.2025.14 Page 3 of 19

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Table 1. Changes in diarrhea incidence and fecal score in nursery pigs challenged with F4 or F18 E. coli
Change
Ref. IBW (kg) Experimental period (d)
Incidence of diarrhea (%) 1 Fecal score 2
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F4 E. coli
[21] *
Molist et al. 5.0 16 - –0.800
Yi et al. [16] 5.3 14 - 0.644
[22] *
Silveira et al. 6.4 21 9.4 -
Khafipour et al. [17] 6.8 20 - 1.127 *
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F18 E. coli
[23]
Duarte et al. 5.8 28 - 0.913
[24] *
Heo et al. 5.9 28 20.0 -
[25]
He et al. 6.2 28 - 0.524
Liu et al. [26] 6.3 15 0.885 *
[9]
Duarte et al. 6.3 28 - 1.336
Becker et al. [18] 6.4 17 - 1.239
[27]
Garavito-Duarte et al. 6.4 28 - 0.200
Gormley et al. [28] 6.4 28 49.9 * -
[29] *
Jang et al. 6.5 28 - 0.300
Xu et al. [30] 6.6 28 - 0.320
[31]
Deng et al. 6.6 25 - 0.133
[32]
Kim et al. 6.7 18 - 0.910
[33] *
Li et al. 6.9 17 32.9 -
[19] *
Sun et al. 7.0 21 - 0.980
Wong et al. [34] 7.2 28 10.4 * -
[35]
Jinno et al. 7.4 28 - 0.405
Duarte et al. [36] 7.9 20 - 0.985
[37]
Duarte et al. 7.9 28 - 0.170
Chang et al. [20] 8.0 16 - 1.067 *
Number of studies 3 Average change 4
Causes
Incidence of diarrhea Fecal score Incidence of diarrhea (%) Fecal score
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F4 and F18 E. coli 5 18 24.5 0.630
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F4 E. coli 1 3 9.4 0.323
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F18 E. coli 4 15 28.3 0.691
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Diarrhea incidence (%) was calculated as the difference between the positive control (E. coli-challenged group) and the negative control (non-
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challenged group). Fecal score changes represent the difference in average fecal scores between the positive and negative control groups,
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standardized to a 1 to 5 scale. Scores originally reported on a 0 to 3 or 1 to 4 scale were converted to a 1-5 scale. The number of studies reflects
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those included in calculating the average change in diarrhea incidence and fecal score. Average changes were calculated as arithmetic
*
means. P < 0.05. E. coli: Escherichia coli; IBW: initial body weight.
The jejunum has been highlighted as a key site for investigating microbial dynamics and epithelial immune
responses. Studies have utilized jejunal mucosa and tissues to evaluate intestinal health in nursery
pigs [2,12,23,44,45] . As the longest segment of the gastrointestinal tract, the jejunum is the first to encounter
external substances from feed, including not only nutrients but also anti-nutritional and allergenic
compounds that can trigger immune defenses before these reach the hindgut [31,44] . Consequently, the
jejunum is more vulnerable to these external factors than the large intestine. It also plays a central role in
digestion and nutrient absorption and contains immune cells in quantities comparable to other intestinal
regions [46-48] . Moreover, the small intestine harbors a lower microbial density than the large intestine, making
it more susceptible to the direct effects of F18 E. coli. Given these characteristics, the jejunum is a critical
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focus for investigating intestinal health. This review aims to explore the mechanisms and effects of F18