Effects of Oregano Extracts, Alone or in Combination with other Biomolecules, on Growth Performances and Parasitological Parameters of Broiler Chickens Challenged with <i>Eimeria</i> spp.: A Meta-Analysis

<b>ABSTRACT</b>Avian coccidiosis, an intestinal disease caused by <i>Eimeria</i> protozoa, is one of the most economically significant parasitic infections in global poultry production. Rising concerns over antimicrobial resistance have intensified the search for sustainable alternatives to conventional anticoccidial drugs. Among the most promising are phytogenic feed additives, particularly oregano (<i>Origanum vulgare</i>) extracts, which are rich in bioactive compounds such as carvacrol and thymol. This meta-analysis systematically evaluates the effects of dietary oregano extract supplementation-both as a standalone intervention and in combination with other anticoccidial agents or feed additives-on key performance and parasitological outcomes in broiler chickens challenged with <i>Eimeria</i> species. A systematic search of multiple electronic databases identified eight eligible studies published between 2003 and 2023, encompassing 16 independent treatment comparisons. Data were extracted for four primary outcomes: body weight (BW), feed conversion ratio (FCR), oocyst output per gram of feces (OPG), and intestinal lesion scores (LS). Pooled effect estimates were calculated using a random-effects meta-analysis. Between-study heterogeneity was assessed with the I² statistic and Q-tests. Potential publication bias was evaluated via funnel plots and Egger's regression test. Oregano supplementation significantly improved all measured outcomes. Pooled effects were as follows: BW +19.9%, FCR +9.2%, OPG -27.1%, and LS -31.0%. Considerable heterogeneity was observed (I² = %, p < 0.0001), but no significant publication bias was detected (Egger's p > 0.05). Sensitivity analyses confirmed the robustness of the findings. Oregano extracts were associated with significant improvements in growth performance and parasitological parameters in <i>Eimeria</i>-challenged broilers under experimental conditions. Supplementation at 100-300 mg/kg represents a promising natural alternative to conventional anticoccidials. Further research is warranted to optimize dosing protocols and confirm efficacy under commercial production conditions.