A systematic review and meta-analysis of Origanum vulgare impact on egg production and quality in laying hens

This project hosts the protocol, data, and materials for a systematic review and meta-analysis investigating the effects of oregano (Origanum vulgare) supplementation on egg production and quality parameters in laying hens. The primary objective is to quantitatively synthesize evidence from randomized controlled trials to determine the efficacy of oregano, administered as either essential oil or powder, on outcomes including egg production rate, egg weight, yolk color, Haugh units, and shell metrics (thickness, weight). The analysis will evaluate how these effects are moderated by the form of oregano (essential oil vs. powder) and the duration of supplementation (≤ 9 weeks vs. > 9 weeks). The review was conducted following PRISMA guidelines. The study protocol was prospectively registered in PROSPERO (ID: CRD420251049876). Comprehensive searches were performed across six databases (PubMed, ProQuest, Scopus, Web of Science, SID, MagIran) up to January 1, 2026. Data were analyzed using random-effects meta-analysis, with effect sizes reported as unstandardized mean differences and 95% confidence intervals.