Age-specific correlations between microbiota and intramuscular fat deposition metagenome

Intramuscular fat (IMF) is a critical determinant of meat quality, influencing attributes such as color, tenderness, juiciness, water-binding capacity, and flavor. Its deposition is modulated by various factors, including age, breed, nutrition, and environment. However, the dynamic processes underlying IMF accumulation in goats, particularly from a microbial perspective, remain poorly understood. In this study, we investigated the IMF deposition in 1-year-old and 4-year-old Longdong cashmere goats, focusing on phenotypic traits, blood lipid profiles, fat metabolism enzymes, and microbial diversity. We assessed slaughter rate, GR value, IMF content in various muscles (shoulder, longissimus dorsi, leg, and rib), as well as lipid levels (including low-, high-, and very low-density lipoproteins, triglycerides, total cholesterol, and free fatty acids). We also measured fatty acid synthase (FAS) and hormone-sensitive lipase (HSL) levels in digestive glands (liver, pancreas, and duodenum) and evaluated short-chain fatty acid (SCFA) concentrations. Spearman correlation analysis was employed to explore relationships between phenotypic traits, physiological markers, and microbial communities. Our results reveal that GR value, shoulder IMF content, and key blood lipid indicators increased significantly with age (p<0.05). Notably, in 4-year-old goats, LPL content in the liver and duodenum was significantly reduced, HSL levels in abomasal chyme were lower, and FAS content in colonic chyme was elevated. Yearling goats displayed higher pH and greater concentrations of valeric and isovaleric acids in the rumen, alongside higher levels of acetic, propionic, and isovaleric acids in the colon. Significant differences in alpha and beta diversity were observed between age groups, with Chao1 and ACE indices in the rumen and abomasum being notably higher in mature goats. Correlation analysis revealed that microbial taxa such as CAG-791, Sodaliphilus, and Clostridium_R in the rumen, and Copromonas in the colon, were positively correlated with GR value and IMF content. These findings underscore the pivotal role of rumen and colon microbiota in the regulation of IMF deposition in Longdong cashmere goats, offering potential avenues for enhancing meat quality through microbial modulation.