Effects of Stocking Density on Fatty Acid Metabolism by Skeletal Muscle in Mice

SIMPLE SUMMARY: Appropriate stocking density is one of the most basic guarantees for experimental animals, and it is also a prerequisite for ensuring the accuracy and credibility of experimental data science. Stocking density, which is related to gut microbiota, affects laboratory mouse health. The aim of this study is to evaluate whether the stocking density of experimental animals affects the gut microbiota, fatty acid metabolism, and muscle quality, and ultimately affects their welfare. According to our results, medium stocking density improves gut microbiota, fatty acid metabolism, and muscle quality in experimental animals. ABSTRACT: Specific pathogen-free (SPF) grade laboratory animals are kept in specific cages for life. The limited space could affect the characterization of colonization and dynamic changes related to gut microorganisms, and affect adipokines, even further affecting the fat synthesis and muscle quality of animals. The objective of this study was to analyze the stocking density on the dynamic distribution of gut microbiota, fat synthesis and muscle quality of SPF grade Kunming mice. Three housing densities were accomplished by raising different mice per cage with the same floor size. Kunming mice were reared at low stocking density (LSD, three mice a group), medium stocking density (MSD, 5 mice a group), and high stocking density (HSD, 10 mice a group) for 12 weeks. The results demonstrated that the stocking density affected intestinal microbial flora composition. We found that compared with the MSD group, the abundance of Lactobacillus in the LSD group and the HSD group decreased, but the abundance of unclassified_Porphyromonadaceae increased. Moreover, fat synthesis and muscle quality were linked to the intestinal microbial flora and stocking density. Compared with the LSD group and the HSD group, the MSD group had a more balanced gut flora, higher fat synthesis and higher muscle quality. Overall, this study demonstrated that stocking density could affect gut microbiota composition, and reasonable stocking density could improve fat synthesis and muscle quality. Our study will provide theoretical support for the suitable stocking density of laboratory animals.