Peer-reviewed publication · Livestock · In the living system
Broilers fed humic substances carried fewer antimicrobial‑resistant E. coli isolates.
Broilers fed these humic substances carried fewer resistant caecal E. coli isolates in this one trial, which measured resistance in the laboratory, not infection or the removal of any pathogen.
Pipová et al., 16 April 2025. Poultry Science 104(7):105175.
Scope, material and route
- Studied
- Male Ross 308 broilers, day 1 to day 37
- Design
- Controlled feeding trial with two groups
- Material
- A commercial leonardite-derived feed additive, at least 65 percent humic acids and 5 percent fulvic acids
- Route
- Feed
- Exposure
- 0.7 percent of the diet. Study exposure, not application guidance.
- Duration
- 37 days
Study design
Standard diet
40 birdsHoused in pens of 10.
- Isolates tested58
- Resistant to at least one antimicrobial52 of 58 (89.7 percent)
- Multidrug resistant25 of 58 (43.1 percent)
Plus 0.7 percent humic substances
40 birdsHoused in pens of 10.
- Isolates tested60
- Resistant to at least one antimicrobial41 of 60 (68.3 percent)
- Multidrug resistant12 of 60 (20.0 percent)
More study details
- Research question
- Does dietary humic substance supplementation change the phenotypic antimicrobial resistance of caecal E. coli in broilers?
- Experimental unit and sample size
- 80 birds, 40 per group, housed in pens of 10 on deep litter; 58 control and 60 treatment isolates, one per sample
- Comparator
- The same feed without humic substances
- Outcomes measured
- Caecal E. coli counts; susceptibility to 19 antimicrobials by broth microdilution; screening for extended-spectrum beta-lactamase production
Findings
Researchers raised 80 male Ross 308 broilers for 37 days, half on a standard diet and half on the same diet with 0.7 percent leonardite-derived humic substances. They counted E. coli in the caeca and tested isolates against 19 antimicrobials. Birds fed humic substances had lower caecal E. coli counts. Fewer of their isolates were resistant to at least one antimicrobial (68 against about 90 percent) and fewer were multidrug resistant (20 against 43 percent), with significant reductions for ampicillin, trimethoprim, sulfamethoxazole, tetracycline and colistin. Only phenotypic resistance was measured. The proposed mechanism is speculative, and genetic studies would be needed to explain the result.
| Outcome | Comparison or result | Interpretation |
|---|---|---|
| Caecal E. coli count | 7.10 against 8.02 log cfu/g (P < 0.05) | Lower with humic substances |
| Resistant to at least one antimicrobial | 68.3 against almost 90 percent of isolates (P < 0.01) | Fewer resistant isolates |
| Multidrug resistance | 20.0 against 43.1 percent (P < 0.01) | Fewer multidrug-resistant isolates |
| Ampicillin resistance | 21.7 against 53.5 percent (P < 0.001) | Lower |
| Tetracycline resistance | 21.7 against 41.4 percent (P = 0.02) | Lower |
| Colistin resistance | 3.3 against 17.2 percent (P = 0.01) | Lower |
| Ciprofloxacin and nalidixic acid resistance | 15.0 against 27.6 percent (P = 0.09); 33.3 against 34.5 percent (P = 0.90) | No statistically supported difference |
Values are humic substance group first, control second, as reported in the paper. Values are extracted from the source as reported; no raw data were available.
Interpretation and limits
What this record supports
A lower prevalence of phenotypically resistant caecal E. coli in broilers fed this preparation, in one controlled trial.
What remains uncertain
- Mechanism. The authors propose binding of antimicrobials or effects on gene expression; neither was measured.
- Design. Birds were housed in pens, and pen-level clustering was not addressed in the statistics.
- Scope. Phenotypic resistance only, in one flock; genetic resistance determinants were not studied.
Which part of the framework it informs
Environmental conditions
The physical, chemical and management context.
Microbial activity
What microbial communities do within that context.
This record informs this area.Observable function
What can be observed or measured in the host or wider system.
- a Caecal wall
- b Fine digesta
- c Bacteria
- d Mucus layer
Source, funding and review
- Source type
- Peer-reviewed publication
- Associated products
- This record does not assess an associated product.
- Funding and relationships
- Slovak Research and Development Agency and the European Regional Development Fund. The manufacturer of the feed additive is named in the paper. The authors declare no known competing financial interests.
- Review status
- Prepared as an editorial summary. External scientific review has not been completed.
- What was read
- Full text read on PubMed Central.
- Original title
- Effect of feed supplementation with humic substances on phenotypic resistance profiles of Escherichia coli isolates from the ceca of broiler chickens
- Authors
- Pipová M, Jevinová P, Semjon B, Regecová I, Marcinčák S, Nagy J
- Publication
- Poultry Science 104(7):105175, 16 April 2025
- DOI
- 10.1016/j.psj.2025.105175
- Summary prepared by
- Carbon Biome Project
- Date added
- 19 October 2026
- Cite this summary
- Carbon Biome Project. Broilers fed humic substances carried fewer antimicrobial‑resistant E. coli isolates. Evidence library record, added 19 October 2026. carbonbiomeproject.com/evidence/pipova-2025-humic-substances-broiler-e-coli-resistance/
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