Abstract
This systematic review and meta-analysis re-evaluated how dietary caprylic acid (CA) supplementation affects
Campylobacter jejuni
colonisation and growth performance in broiler chickens, and which factors modulate its efficacy. Because caecal colonisation at the end of rearing is a principal determinant of carcass contamination at processing, and because growth performance governs slaughter weight and carcass yield, the two outcomes were treated here not as independent endpoints but as complementary dimensions of a single theme: the microbiological and technological quality of the final poultry product. We searched PubMed, Scopus and Google Scholar for controlled in vivo broiler trials published between January 2000 and July 2025 that administered CA orally and reported quantitative outcomes for caecal
C. jejuni
counts or growth performance. Data were extracted from the primary publications and synthesised with random-effects models, using the mean difference (MD, log10 colony-forming units (CFU) g
−1
) for colonisation and the standardised mean difference (SMD) for growth, with pre-planned subgroup, dose–response and sensitivity analyses. Twelve studies met the eligibility criteria; 11 contributed 15 comparisons to the quantitative syntheses and one could be included only qualitatively. Caprylic acid reduced caecal
C. jejuni
by a pooled −1.46 log10 CFU g
−1
(95 % confidence interval (CI) −2.50 to −0.41;
P
=0.006), with substantial heterogeneity (
I
2
=88.1 %). Route of administration accounted for most of that heterogeneity: in-feed application reduced colonisation by −2.68 log10 CFU g
−1
(95 % CI −3.88 to −1.49;
I
2
=39.0 %), whereas water-based application had no detectable effect (−0.05 log10 CFU g
−1
; 95 % CI −0.68 to +0.58). Growth performance was unaffected overall (SMD +0.16; 95 % CI −0.32 to +0.64;
P
=0.524), but the dose–response analysis showed that inclusion above about 1 % of feed depressed feed intake and body weight while conferring no additional antimicrobial benefit. Funnel-plot asymmetry was significant (Egger's test,
P
=0.009) but coincided with the feed-versus-water contrast, so publication bias and genuine subgroup heterogeneity could not be separated. Caprylic acid is therefore a credible component of antibiotic-free
Campylobacter
control in broilers when delivered in feed at approximately 0.35 % to 0.875 % but not when delivered in drinking water.