Effects of Dietary Thymus vulgaris on Laying Hens: A Systematic Review and Meta‐Analysis of Productive Performance and Egg Quality

ABSTRACT Objectives Natural alternatives to synthetic additives are being explored as a means to enhance laying hen performance and egg quality. The study conducted a systematic review and meta‐analysis to evaluate the effect of dietary supplementation with Thymus vulgaris (thyme) on productive performance and egg quality in laying hens. Methods A comprehensive search of databases identified 18 eligible studies. Data were analysed using random‐effects models, with subgroup analyses based on the thyme form (powder, essential oil, extract) and supplementation duration (≤ 8 weeks, > 8 weeks). The unstandardized mean difference was used to calculate the effect size, and confidence intervals were generated to estimate the range of the true effect size. Results Thyme significantly improved egg weight, egg mass, yolk colour, yolk index and shell thickness (p < 0.05), with very large effect sizes for egg weight and mass. However, albumen quantity decreased, while egg production rate, Haugh unit, and shell weight remained unchanged. Powdered thyme was particularly effective at enhancing egg weight and mass, while essential oils and extracts improved yolk colour. Longer supplementation periods (> 8 weeks) yielded greater benefits for egg mass and weight, whereas shorter durations (≤ 8 weeks) improved shell thickness. Conclusions These findings suggest that thyme supplementation, particularly in powdered form and over extended periods, can enhance egg quality, offering a natural alternative to synthetic additives. This research demonstrates thyme's efficacy as a phytogenic feed additive, offering a natural solution to improve egg quality and meet the rising demand for sustainable and high‐quality poultry products. Summary Thyme supplementation improves egg weight, egg mass, yolk colour and shell thickness in laying hens. Powdered thyme shows the most significant benefits for egg weight and mass. Longer supplementation periods (> 8 weeks) enhance yolk colour and egg quality traits. Thyme offers a natural, sustainable alternative to synthetic feed additives in poultry production.