Abstract
Skatole (3-methylindole), one of the most malodorous compounds from swine manure, poses serious risks to animal, human, and environmental health. Therefore, it has become a serious concern in livestock farming. Saccharomyces cerevisiae is widely used in livestock feed to improve growth and intestinal health. However, its role in reducing skatole production and the underlying mechanisms remains unclear. To explore this idea, an in vitro fermentation study was conducted using pig rectal contents. We evaluated skatole levels by high-performance liquid chromatography and profiled microbiota and metabolites using 16S rRNA sequencing and ultra-high-performance liquid chromatography-tandem mass spectrometry. S. cerevisiae supplementation significantly reduced pH and skatole concentration in the fermentation broth. There was a significant increase in the abundance of Lysinibacillus, Sojibacillus, Bacillus, Sphingobacterium, Moraxella, and Proteiniclasticum, along with a significant decrease in Peptostreptococcus, Prevotellaceae_NK3B31_group, Prevotellaceae_UCG_001, Enterococcus, Desulfovibrio, Veillonella, and Streptococcus. The abundance of Sphingobacterium, Moraxella, and Proteiniclasticum was negatively correlated with pH and skatole, whereas Desulfovibrio and Streptococcus showed a positive correlation. Metabolomic analysis revealed that methyl (indol-3-yl)acetate, indoxyl sulfate, and 3-methylindole were significantly downregulated. Meanwhile, 5-hydroxyindole-2-carboxylic acid, Dl-indole-3-lactic acid, 5-hydroxyindole, 4-aminoindole, 5-hydroxytryptophol, and indole-3-acetic acid were significantly upregulated. The levels of 3-methylindole were positively correlated with indoxyl sulfate and negatively correlated with Dl-indole-3-lactic acid and 5-hydroxytryptophol. These results suggest that S. cerevisiae reduces skatole amounts via modulation of specific microbial populations and tryptophan metabolism. This study provides a theoretical basis for developing microbial strategies to reduce odor in pig farming.IMPORTANCESkatole is one of the most odorous compounds in the gastrointestinal tract and feces of animals, which poses a serious threat to animal, human, and environmental health. Therefore, taking measures to reduce skatole emissions is essential for sustainable livestock development. Saccharomyces cerevisiae as a beneficial feed additive can not only improve feed digestibility and growth performance, reduce pathogenic bacteria, and improve animal health, but also reduce odor emissions from livestock and reduce the impact of livestock production on the environment. This study explored the role of S. cerevisiae in reducing skatole production and the underlying mechanisms. The result showed that S. cerevisiae reduced skatole content by regulating specific microbial populations and tryptophan metabolism. These findings provide a theoretical reference for developing more effective microbial agents to reduce odor emissions in pig farming.