Effects of Increased Housing Space Without Altering Stocking Density on Body Weight, Stress, and Gut Microbiome in Broiler Chickens

Effective poultry management practices that promote chicken health are crucial for producing higher-quality chicken meat at a lower cost. This study examined the hypothesis that increasing space while maintaining stocking density may positively impact poultry health. We evaluated body weight (BW) as an indicator of growth, stress markers, and the composition of the gut microbiome by comparing two housing sizes: smaller (control) and larger (treatment) spaces, with 10 birds per space and a stocking density of 12.3 birds/m². Chickens in the larger space had 15% higher BW (<i>p</i> = 0.06) compared to those in the smaller space when significance was evaluated at <i>p</i> < 0.10. Stress indicators such as blood cortisol (acute) and brain <i>FKBP51</i> did not differ significantly. Faith’s phylogenetic diversity was marginally higher in the larger space (<i>p</i> = 0.05), and microbial communities differed significantly between the two groups. The relative abundance of several genera, including <i>Clostridium_sensu_stricto_1</i> (<i>p</i> = 0.02), <i>Lactobacillus</i> (<i>p</i> = 0.03), and <i>Paracoccus</i> (<i>p</i> < 0.01), was greater in the larger space, whereas <i>Turicibacter</i> (<i>p</i> = 0.02), <i>Escherichia–Shigella</i> (<i>p</i> = 0.01), and <i>Lysinibacillus</i> (<i>p</i> = 0.01) were more abundant in the smaller space. The larger and smaller spaces were associated with a significant (<i>p</i> < 0.05) increase in the abundance of 39 and 25 MetaCyc pathways, respectively, involved in amino acid and nitrogen metabolisms. These findings suggest that increasing housing space without altering stocking density or additional treatments may improve both growth and gut microbiome health in broilers. Our results provide insights into the relationship between chicken housing environments and the gut microbiome.