# Gut Microbiome Signatures of Aging Associated with Intramuscular Fat Deposition in Tan Sheep

## TL;DR

This study finds that gut bacteria in older Tan sheep are linked to higher fat deposition in meat, suggesting microbial modulation could improve mutton quality.

## Contribution

The study identifies specific gut microbiome signatures associated with aging and intramuscular fat deposition in Tan sheep.

## Key findings

- Mature Tan sheep have higher intramuscular fat and serum lipid levels compared to yearlings.
- Colon bacteria like Copromorpha and RUG420 correlate positively with fat deposition and serum lipids.
- Cryptobacteroides in the colon correlates negatively with fat and positively with short-chain fatty acids.

## Abstract

Intramuscular fat (IMF) is a key factor in determining meat quality and palatability. Identifying the regulators of IMF deposition is essential for developing strategies to improve meat quality. Previous studies have shown that certain dietary additives and candidate genes promote fat accumulation. This present study highlights the significant influence of age on IMF deposition in Tan sheep. Mature sheep exhibit higher IMF content in the shoulder and rump muscles, elevated serum lipid levels, and increased concentrations of lipolytic enzymes in the liver and pancreas compared to yearlings. These age-related changes were associated with shifts in the gut microbiota, particularly the colonic bacteria Copromorpha, RUG420 and Cryptobacteroides. These findings underscore the potential role of specific colonic bacteria in regulating IMF deposition and provide a novel approach to enhancing mutton quality through microbial modulation.

Intramuscular fat (IMF) content determines marbling levels and influences the sensory and edible qualities of livestock meat. Its deposition is influenced by the animal’s age and gut microbial community. This study assessed age-related differences in IMF deposition and shifts in gut microbiota between yearlings (1-year-old) and mature (4-year-old) grazing Tan sheep. Then correlations among these factors were examined to investigate the potential role of gut bacteria in IMF deposition. The results demonstrated that mature sheep exhibited higher IMF content in shoulder and rump muscles (p < 0.05), elevated serum lipid levels (p < 0.001), and increased lipolytic enzyme abundances in the liver and pancreas (p < 0.05), compared with yearlings. In contrast, the concentrations of acetate and propionate in ruminal and colonic contents were lower in mature sheep (p < 0.05), despite a higher abundance of lipolytic and synthetic enzymes in colonic content (p < 0.05). Gut microbial diversity differed between age groups, particularly in the rumen and colon, with clear shifts in specific bacterial taxa. Correlation analyses revealed that the abundance of Copromorpha and RUG420 in the colon were positively correlated with IMF content in shoulder and rump muscles, and serum lipid levels (including free fatty acids, FFA; low-density lipoprotein, LDL; high-density lipoprotein, HDL; and very-low-density lipoprotein, VLDL), but negatively correlated with propionate content (|r| > 0.45, FDR < 0.05). Conversely, the abundance of Cryptobacteroides in the colon was negatively correlated with IMF content in shoulder muscle (r < −0.6, FDR < 0.05), and with the levels of triglyceride (TG), LDL, HDL, and VLDL, while showing positive correlations with acetate and propionate contents (r > 0.45, FDR < 0.05). These findings highlight the potential role of specific colon bacteria (Copromorpha, RUG420, and UBA5905) in IMF deposition, identifying them as candidate bacteria for further investigation regarding their effects on meat quality.