Across 29 controlled trials, dietary butyrate was associated with significant pooled improvements in egg production and several quality traits. Results varied considerably between studies, however, and neither formulation nor feeding duration provides a simple basis for choosing an optimal supplementation strategy.
Butyrate supplementation in laying hens has been studied with different chemical sources, formulations, doses and feeding periods. When those trials are pooled, the overall direction of the results is positive. The size of the response, however, varies widely from one study to another.
A systematic review and meta-analysis by Hassanpour and colleagues combined 29 controlled studies and examined seven production and egg-quality outcomes. All seven showed statistically significant pooled differences in favour of butyrate. At the same time, heterogeneity was high for every outcome, with I² values ranging from 75.0% to 96.6%.
The authors conclude that coated butyrate salts were the most effective formulation and that the benefits depend on using coated products and appropriate supplementation periods. Their own analyses support a more cautious reading: formulation and duration were associated with part of the variation between studies, but much of it remained unexplained.
The pooled effects were positive across all seven outcomes
The review covered studies identified through six databases up to July 2026. Supplementation lasted from 4 to 44 weeks, with doses ranging from 0.105 to 15 g/kg. The trials involved different laying-hen genotypes and included sodium and calcium butyrate, coated products, butyric acid and glyceride-based forms.
Using random-effects models, the researchers calculated an average increase in egg production of 1.58 percentage points compared with control groups, with a 95% confidence interval of 0.90 to 2.17. Egg mass increased by 1.15 g/day (95% CI 0.66 to 1.64).
For egg weight, the pooled difference was 0.48 g (95% CI 0.01 to 0.96; P=0.043). Haugh unit increased by 1.25, shell thickness by 0.014 mm, shell strength by 0.14 kgf and yolk colour by 0.26 units on the 1–15 Roche scale.
The variation behind these averages was substantial. I² reached 96.6% for egg weight, 89.6% for egg production and 89.4% for shell strength; even Haugh unit, the outcome with the lowest reported heterogeneity, had an I² of 75.0%. Sensitivity analysis did not indicate that a single study was driving the main pooled results. A pooled figure such as +1.58 percentage points is an average across very different experiments, not the response to expect from a particular flock, diet or commercial product.
Feeding duration did not follow one pattern
For subgroup analysis, the authors separated studies lasting nine weeks or less from those running for more than nine weeks.
Egg production remained significantly higher with butyrate in both groups: +2.09 percentage points in the shorter-duration studies and +1.15 points in the longer studies. Egg mass and shell thickness were also significantly improved in both duration categories.
Other traits differed. Egg weight, Haugh unit and shell strength reached statistical significance in the ≤9-week subgroup but not in the >9-week subgroup. Yolk colour showed the opposite pattern, with a significant pooled increase only in studies lasting more than nine weeks.
These are comparisons between different sets of studies, not between shorter and longer feeding periods applied under the same experimental conditions. They show where effects were detected, not how the response would change if supplementation were extended or shortened.
The subgroup analyses and the meta-regression do not always agree. Egg weight improved significantly in trials of nine weeks or less and not in longer trials, yet duration was not a significant moderator of egg weight in the meta-regression. For shell thickness, the subgroup estimate was larger in trials lasting more than nine weeks (+0.019 vs +0.011 mm), whereas the meta-regression reported larger effects with shorter supplementation. Duration was a significant moderator for every outcome except egg weight.
The data point to an association between duration and several responses, but not to a general rule that shorter or longer supplementation is preferable.
Formulation accounted for part of the differences between trials
The authors also examined the studies according to product formulation and butyrate source.
Among the three moderators tested, formulation accounted for the largest share of between-study heterogeneity for every outcome, with R² values from 16.4% to 26.4%. These values describe how much of the heterogeneity a moderator accounts for; they are not a measure of efficacy.
Analysed as a broad category, coated formulations showed significant pooled effects for all seven outcomes. Uncoated products were significant for five – egg production, egg weight, egg mass, Haugh unit and shell thickness – but not for shell strength or yolk colour. Glyceride-based products were significant for egg production, shell thickness and shell strength, but not for egg weight, egg mass, Haugh unit or yolk colour.
The breakdown by chemical source is more revealing. Sodium butyrate and coated sodium butyrate each showed significant effects on six of the seven outcomes (sodium butyrate not on yolk colour, coated sodium butyrate not on egg weight), and neither had the larger estimate across the board. Uncoated calcium butyrate was significant only for shell thickness, while none of the reported subgroup effects for butyric acid or coated butyric acid reached statistical significance.
The evidence base was not equally large for all categories. Coated calcium butyrate was represented by only one trial, so its place among the most effective coated salts in the authors’ conclusion rests on a single study. Butyric acid and coated butyric acid were each represented in two studies. These subgroups cannot carry the same weight as the more frequently studied forms.
The point estimates do not rank the formulations consistently either. For egg production, coated, uncoated and glyceride-based formulations all had significant pooled effects. The numerical estimate for glycerides was the largest, at +2.23 percentage points, but heterogeneity within that subgroup was 92.5% and the confidence interval was wide. For egg weight, coated and uncoated products both had a pooled estimate of +0.32 g; the larger estimate for glycerides was not statistically significant.
Formulation, in short, is associated with differences between studies, but no single formulation was consistently superior across the outcomes and production conditions represented in the dataset.
High residual heterogeneity limits prescriptive conclusions
After the moderators had been considered, residual I² still ranged from 55.4% to 95.5%.
The studies differed in factors such as genotype, age, production stage, basal diet, management, butyrate dose and experimental duration. Not all of these could be examined as moderators in the meta-analysis, leaving much of the variation unexplained.
Reporting quality in the primary literature is a further limitation. Using the SYRCLE risk-of-bias tool, the reviewers found that sequence generation, allocation concealment and outcome-assessment blinding were rated unclear in 23 to 27 of the 29 studies, largely because these details were not reported.
Publication-bias analyses were mixed. Begg’s and Egger’s tests indicated possible bias for egg production. For shell strength, Begg’s test produced a signal while Egger’s test did not. Trim-and-Fill analysis found no missing studies, and the funnel plots did not show clear asymmetry. Some caution over the magnitude of these two pooled estimates is warranted, although the tests do not consistently point to bias.
Several questions that matter for feed formulation remain open. The analysis does not identify an optimal dose, establish the economic return from different forms of butyrate or provide direct head-to-head evidence across all formulations. Mechanisms proposed to explain changes in performance or egg quality were not demonstrated by the meta-analysis itself.
The authors call for more direct comparisons between formulations, dose-response studies and economic evaluation. Better reporting of randomisation and other methodological details would also make future pooled estimates easier to interpret.
On the current evidence, butyrate supplementation was associated with modest average improvements across the production and egg-quality traits examined, while the size of the response varied markedly between studies. Formulation and duration explained part of that variation, but neither supplied a universal rule for practical use.
Source
Hassanpour H, Karimi-Shayan T, Fallah AA, Ahmadipour B. Impact of different butyrate forms on egg performance and quality in laying hens: a systematic review and meta-analysis. BMC Veterinary Research. Article in Press, published online 24 September 2026. https://doi.org/10.1186/s12917-026-05945-3
Original article © The Author(s) 2026. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0): http://creativecommons.org/licenses/by-nc-nd/4.0/
Editorial article by the Zootecnica – Poultry Magazine editorial team, based on the cited study.
