Protein feed-driven regulation of pig intestinal microbiota: Mechanisms underlying odor emission mitigation and development of sustainable deodorizing formulations

Livestock farming significantly contributes to anthropogenic greenhouse gas emissions and malodorous pollutants, exacerbating global environmental degradation. Despite the crucial role of protein feeds in regulating gas emissions and enhancing pork production efficiency, the mechanisms by which different protein feeds regulate odors remain unclear. This study employed an in vitro simulated fermentation and in vivo feeding trials to explore the effects of eight protein feeds in China on odor mitigation through regulation of pig gut microbiota. Results demonstrated that protein content and amino acid composition were key factors influencing odor emissions. Notably, the cottonseed meal group exhibited the highest levels of odor (68.67 ± 58.13 ppm) and showed enrichment of the genus Megasphaera. Correlation analysis revealed positive associations between Megasphaera and the production of $H_2$S, NH₃, $H_2$, and CO₂. KEGG pathway analysis indicated that the cottonseed meal group displayed a higher abundance of metabolic pathways compared to other experimental groups, with Megasphaera positively correlating with multiple metabolic pathways, including amino sugar and nucleotide sugar metabolism. In contrast, corn germ meal-H and rapeseed meal-J groups had lower odor levels (12 ± 5.33 ppm and 16.17 ± 6.18 ppm, respectively), negatively associated with Bacillus and unclassified_c__Bacilli. Additionally, feeding trials demonstrated that rapeseed meal-based feed reduced NH₃ and $H_2$S emissions in pig houses by 47.75% and 54.2%, respectively, without compromising pig production performance. These findings clarified protein feeds’ role in odor regulation and laid a scientific foundation for balancing pig industry sustainability and environmental degradation. However, odor metabolism molecular mechanisms in key bacteria and others still require in-depth study.