The stakes are considerable. Campylobacter is a leading bacterial cause of food-borne illness worldwide, and poultry meat is the dominant route of human exposure, whether through undercooked products or cross-contamination in the kitchen. In commercial broiler flocks, colonisation rates commonly range from about 55 percent to 100 percent, meaning the chicken intestinal tract functions as a vast reservoir of the pathogen. At slaughter, leakage of caecal contents can contaminate carcass surfaces, amplifying risk along the entire food chain. Because the caecal load of Campylobacter at the end of rearing is the strongest single predictor of carcass contamination, interventions that act inside the living bird have long been a priority for food-safety researchers.

The new analysis, conducted by Muhammet Kuddusi Erhan of Ağrı İbrahim Çeçen University in Türkiye, searched PubMed, Scopus and Google Scholar for controlled in vivo broiler trials published between January 2000 and July 2025. Following PRISMA 2020 guidelines, the review identified twelve eligible studies, eleven of which contributed fifteen separate comparisons to the quantitative syntheses. The author used random-effects models, taking the mean difference in log10 colony-forming units per gram of caecal contents as the effect measure for colonisation, and the standardised mean difference for growth performance, with pre-planned subgroup, dose-response and sensitivity analyses layered on top.

The headline result is striking. Across all routes of administration, caprylic acid supplementation reduced caecal C. jejuni loads by a pooled 1.46 log10 CFU per gram, a statistically significant reduction with a 95 percent confidence interval running from 2.50 to 0.41. But the pooled figure concealed enormous heterogeneity between studies, with an I-squared value of 88.1 percent, indicating that the trials were estimating genuinely different underlying effects rather than a single common one. Locating the source of that inconsistency turned out to be the most scientifically valuable part of the entire exercise.

When the comparisons were stratified by route of administration, the picture snapped into focus. In-feed application reduced colonisation by a pooled 2.68 log10 CFU per gram, with only moderate residual heterogeneity, whereas delivery via drinking water produced essentially no detectable effect at all. The formal test for subgroup differences was unambiguous, and the fall in heterogeneity from 88.1 percent overall to 39.0 percent within the in-feed subgroup identified the delivery matrix as the principal determinant of efficacy. Within the in-feed trials, 0.7 percent caprylic acid given for three to ten days cut caecal counts by 2.0 to 3.9 log10 units in three independent experiments, spanning both prophylactic use in young chicks and therapeutic use in market-aged birds.

The mechanism behind this route dependence is biologically plausible. Caprylic acid is bactericidal against C. jejuni in vitro at low millimolar concentrations, inserting into and disrupting bacterial membranes, interfering with the electron transport chain, lowering intracellular pH and inhibiting key metabolic enzymes. Feed, however, provides a lipophilic, slow-release matrix in which the undissociated fatty acid can survive passage through the upper gastrointestinal tract. Aqueous formulations, by contrast, appear to be rapidly absorbed by enterocytes before ever reaching the caeca, where C. jejuni colonises the mucus layer and is shielded from fatty acid activity. Consistent with this interpretation, raising the water-borne concentration thirty-two-fold produced no graded response whatsoever, suggesting the limiting step is survival en route rather than the quantity administered.

Equally important is what the analysis found about growth. Across nine comparisons, caprylic acid had no overall effect on growth performance, with a pooled standardised mean difference of +0.16 that was statistically indistinguishable from zero. This growth neutrality is what makes the compound economically viable as a pathogen-reduction tool. But the dose-response analysis revealed a clear ceiling. In-feed concentrations between roughly 0.35 percent and 0.875 percent produced consistent reductions of 2.2 to 3.6 log10 units, while higher concentrations became both weaker on average and markedly less reproducible. At 1.4 percent of feed, body weight was significantly depressed, with feed consumption falling steadily across the dose series. Palatability, it seems, imposes an upper practical limit before any pharmacological ceiling is reached, although reduced intake alone does not fully explain the loss of antimicrobial efficacy, since total caprylic acid consumption still rose with dose.

The author is candid about the limitations of the evidence base. Funnel-plot asymmetry was statistically significant, which in principle signals publication bias, but in this dataset the asymmetry maps precisely onto the feed-versus-water contrast: the imprecise, strongly negative comparisons are the in-feed trials, and the precise, near-null comparisons are the drinking-water trials. Genuine subgroup heterogeneity can generate funnel asymmetry as readily as selective publication, and with only six colonisation comparisons no statistical procedure can adjudicate between the two explanations. The pooled estimate of 1.46 log10 units should therefore be read as an upper bound on the true average in-feed effect. A leave-one-out analysis showed the direction of the effect was robust to the removal of any single comparison, though its statistical significance depended marginally on the largest trial. The apparently positive growth responses to caprylic acid blends also warrant caution, since in those comparisons the compound’s contribution could not be separated from that of other bioactive ingredients.

Why does the magnitude matter so much? Quantitative risk assessment indicates that a two-log reduction in carcass contamination would reduce the incidence of human campylobacteriosis associated with chicken meals roughly thirty-fold. The in-feed effect documented here, averaging 2.68 log10 units, comfortably exceeds that threshold, which is why the author argues that caprylic acid deserves a place within integrated Campylobacter control strategies for producers seeking antibiotic-free alternatives. The analysis also suggests that micro-encapsulated or otherwise protected formulations, which prolong the presence of fatty acids in the lower gut, deserve direct examination, and that future work should explore combinations with competitive exclusion cultures, bacteriophages or vaccination.

The broader significance of the study lies in its framing. Rather than treating antimicrobial efficacy and growth performance as unrelated endpoints, the review evaluates caprylic acid explicitly as a product-quality intervention, in which microbiological safety and zootechnical performance are assessed jointly. An additive that lowers pathogen load at the cost of impaired growth, or that improves growth without any food-safety benefit, has limited practical value. By converging on the same recommendation from both directions, an effective in-feed range of approximately 0.35 to 0.875 percent that delivers the antimicrobial benefit without a measurable productivity cost, the analysis offers the poultry industry something it has rarely had on this question: a quantitatively grounded, honestly caveated prescription. As antibiotic growth promoters remain banned in the European Union and increasingly restricted elsewhere, evidence of this kind may prove essential to making antibiotic-free poultry production both safer and commercially sustainable.

Subject of Research: Effects of dietary caprylic acid on Campylobacter jejuni colonisation and growth performance in broiler chickens

Article Title: Dietary caprylic acid, Campylobacter jejuni colonisation and product quality in broilers: a systematic review and meta-analysis

Article References: Dietary caprylic acid, Campylobacter jejuni colonisation and product quality in broilers: a systematic review and meta-analysis. (n.d.). https://doi.org/10.5194/aab-69-477-2026

Image Credits: AI Generated

DOI: 10.5194/aab-69-477-2026

Keywords: caprylic acid, Campylobacter jejuni, broiler chickens, food safety, meta-analysis, feed additives, medium-chain fatty acids, poultry production, antibiotic-free, dose-response, gut microbiology, zoonoses