# Compost fermented with thermophilic Bacillaceae reduces heat stress–induced mortality in laying hens through gut microbial modulation

## TL;DR

Fermented compost improves laying hens' survival during heat stress by changing gut bacteria and increasing beneficial fatty acids.

## Contribution

The study shows that compost fermented with thermophilic Bacillaceae reduces heat stress mortality in hens via gut microbial modulation.

## Key findings

- Compost extract reduced hen mortality during heat stress.
- Compost increased beneficial gut bacteria like Lactobacillus and Blautia.
- Compost increased acetate and butyrate while reducing harmful bacteria like Romboutsia.

## Abstract

Heat stress (HS) adversely affects poultry health and productivity. Recently, it has been suggested that the gut microbiota may play a role in host resilience to HS, although the details of its mechanism remain unclear. Here, the heat tolerance-related effects of dietary supplementation of compost fermented by the thermophile Bacillaceae were explored using a laying hen model (601,474 hens in total).

In a field study conducted during the summer (maximum temperatures of approximately 35 °C) in eleven hen houses, oral administration of the compost extract resulted in a statistically significant reduction in mortality. Difference-in-differences analysis revealed that the abundances of the genera Lachnospiraceae NK3A20 group, Enterococcus, Ruminococcus 2, Blautia, Lactobacillus, Christensenellaceae R-7 group, and Tyzzerella 4 were significantly increased by compost administration, whereas those of the Prevotellaceae NK3B31 group, Prevotella 9, Romboutsia, Turicibacter, and Escherichia–Shigella were significantly reduced. In addition, to evaluate the relationship between short-chain fatty acids (SCFAs) metabolic profiles and the gut bacterial population, factor analysis combined with feature selection based on multiple machine learning (ML) algorithms was performed. The resulting optimal structural equation model suggested that compost administration led to increases in the levels of the SCFAs acetate and butyrate, as well as decreases in the levels of the genera Romboutsia and Turicibacter.

Oral administration of thermophile-fermented compost to laying hens alleviated HS-induced mortality. Integrative computational evaluations further revealed that the reduction in mortality was linked to structural changes in the gut microbiota composition and SCFA concentrations.

The online version contains supplementary material available at 10.1186/s42523-026-00520-5.