Transcriptomic and Meat Quality Differences in Longissimus Dorsi Muscle of Surgically Castrated Three-Year-Old Kazakh Horses

Although the Kazakh horse is a dual-purpose breed renowned for both milk and meat production, the extent to which surgical castration alters gene expression in its muscles has not yet been fully elucidated. In this study, left longissimus dorsi muscle (LDM) samples were obtained from six Kazakh stallions (W group) and six Kazakh geldings (S group) to comparatively evaluate meat quality parameters, examine histological characteristics in tissue sections, and apply transcriptomic profiling to comprehensively explore the principal regulatory pathways and candidate genes through which surgical castration modulates LDM growth. The results demonstrated that surgical castration did not induce significant alterations in meat color or pH-related parameters. However, cooking loss and shear force values were markedly diminished, accompanied by a marked decrease in muscle fiber cross-sectional area. Transcriptomic analysis identified 848 differentially expressed genes (DEGs) in total, comprising 415 upregulated and 433 markedly downregulated DEGs, which were predominantly enriched in key biological pathways, including actin cytoskeleton regulation. Moreover, eleven core candidate genes, including MYL2, MYL3, and TNNI1, were further screened and identified.