# Effects of selection on production parameters and intestinal microbiota in heritage and modern broiler chickens

## TL;DR

This study shows that genetic selection for faster growth in chickens changes their gut bacteria and may influence growth rates.

## Contribution

The study reveals how genetic selection affects gut microbiota diversity and metabolic pathways in broiler chickens.

## Key findings

- Modern broiler lines had lower gut microbial diversity compared to heritage chickens.
- Selected lines showed higher abundance of certain bacteria like Escherichia and Streptococcus.
- Predicted metabolic pathways related to nucleotide and biotin biosynthesis were increased in fast-growing lines.

## Abstract

Genetic selection has improved feed efficiency and growth in broiler chickens. Intestinal microbiota plays an important role in gut functions and host metabolism; however, it is unclear whether selection for rapid growth has affected intestinal microbiota. The objective of the study was to determine the effects of genetic selection on intestinal microbiota in broiler chickens.

Heritage (Athens Canadian Random Bred: ACRB), slow- and fast-growing (SG, FG) chickens were raised under similar conditions for 35 d. 16S rRNA sequencing was performed on ileal and cecal luminal (IL-L and CE-L, respectively) and mucosal bacterial populations, and data were analyzed using the qiime2 platform, differential abundance, and metabolic pathways.

The relative abundance of the genus Turicibacter was elevated (P < 0.05) at hatch compared to 48 h before hatch; while at species level, Clostridium celatum was increased (P < 0.05) at hatch. During the post-hatch period, body weight was higher in the SG and FG groups than in the ACRB group at each time point from d 13 to 35. In IL-L, richness (d 14) was lower (P < 0.05) in ACRB compared to FG and SG lines, respectively. In CE-L, richness and Shannon index were reduced (P < 0.05) in ACRB compared to FG lines only on d 35. The Shannon index was significantly (P < 0.05) lower in ACRB birds compared to FG birds on d 35. The relative abundance of genus Escherichia was higher (P < 0.05) in SG compared to other lines. FG birds were characterized by the highest (P < 0.05) Streptococcus level. Relative abundance of most of the identified species were affected only by time post-hatch and only the relative abundance of a single species Lactobacillus salivarius was higher (P < 0.05) in FG compared to ACRB birds. Predicted metabolic pathways related to biosynthesis of nucleotides and biotin, especially in the cecum, were increased in SG lines.

These results indicate that selection for growth has affected intestinal microbiota as bacterial diversity was different in the ileum and cecum which could partly explain growth rate differences among heritage and modern lines. In addition, the increased predicted metabolic pathways in the ileum of SG birds could positively affect growth rate, and further research is needed to elucidate this hypothesis.

The online version contains supplementary material available at 10.1186/s40104-026-01360-8.