Mitigation of odor emissions by replacing soybean meal with unconventional protein ingredients: Assessment via in vitro simulated fermentation

To address the challenges of odor pollution from livestock farming and the need for resource conservation and reduced feed consumption, this study utilized an in vitro fermentation model to simulate the hindgut fermentation of fattening pigs. With soybean meal serving as the control, the impacts of eight unconventional protein feed ingredients—specifically defatted rice bran, peanut meal, two types of sesame meal, palm kernel meal, sunflower meal, dephenolic cottonseed protein, and corn gluten meal—on intestinal microbiota composition and metabolic activity were systematically evaluated. Fermentation end-products and gas emissions were quantified, and microbial community structure was analyzed using 16S rRNA gene sequencing. The palm kernel meal enhanced microbial diversity by enriching the Subdoligranulum and increased butyric acid production. The abundance of Lactobacillus enriched in the sesame meal-J was negatively correlated with the generation of H 2 S and H 2 , while Megasphaera and Streptococcus were positively correlated with the production of sulfur-containing gases and isovaleric acid. The microbial metabolic activity in the functional pathway of cysteine and methionine in the sesame meal-Q group increased by 60.4%, positively regulating H 2 S emissions. Through the regulatory framework of "nutrition-microbiota-odor emissions", this study revealed the mechanism by which unconventional protein feed ingredients regulate the gut microbiota of growing pigs to exert nutritional support and odor reduction effects. It provides a theoretical basis for the development of environmentally friendly feed and the reduction of soybean meal usage. • The gut microbiota of growing pigs produced different gases depending on protein feeds. • Palm kernel meal enriched Subdoligranulum and increased butyric acid production. • Lactobacillus abundance was negatively correlated with H 2 S and H 2 production. • Megasphaera and Streptococcus were positively correlated with H 2 S and isovaleric acid. • The cysteine and methionine metabolic pathways were positively associated with H 2 S emissions.