Impact of different butyrate forms on egg performance and quality in laying hens: a systematic review and meta-analysis

Abstract

This systematic review and meta-analysis evaluated the effects of different butyrate formulations on egg production and quality in laying hens, and examined the moderating effects of formulation type and supplementation duration. This systematic review and meta-analysis was conducted following the PRISMA 2020 guidelines. A systematic search of PubMed, Scopus, Web of Science, CAB Abstracts, SID, and MagIran (to July 2026) identified 29 controlled trials of butyrate supplementation in laying hens. We performed a meta-analysis using random-effects models to pool MD with 95% CIs. Subgroup analyses examined butyrate form (salts, coated, glycerides) and duration (≤ 9 vs. >9 weeks). Heterogeneity was assessed (I², Q-test), and meta-regression quantified moderator effects, SYRCLE assessed risk of bias. Results demonstrated significant improvements in all measured outcomes: egg production, egg weight, egg mass, Haugh unit, shell thickness, shell strength, and yolk color. Subgroup analysis revealed that coated butyrate salts (sodium and calcium) were the most effective formulation, consistently enhancing multiple parameters. The meta-analysis identified a critical time-dependent efficacy: benefits for egg weight, shell strength, and Haugh unit were significant only in shorter supplementation periods (≤ 9 weeks), while yolk color improvement was exclusive to longer administration (> 9 weeks). Meta-regression indicated that formulation was associated with the largest proportion of explained variance among the tested moderators (R² up to 26.4%), followed by duration (up to 15.8%) and source (up to 14.7%). High heterogeneity (I²: 75.0–96.6%) was observed across outcomes, although sensitivity analysis confirmed a consistent direction of effect. Butyrate supplementation enhances layer performance and egg quality, but its efficacy is strictly dependent on using coated formulations and optimized supplementation timelines. These findings help explain some of the previous inconsistencies in the literature and provide evidence-based guidance for employing butyrate as a targeted nutritional strategy in poultry production. OSF ( https://doi.org/10.17605/OSF.IO/A2ZR6 ).