Rumen unprotected glucose tends to promote intramuscular fat deposition via microbial volatile fatty acid-mediated metabolic reprogramming in cattle: a multi-omics perspective through the rumen-jejunum axis.

Abstract

The regulatory effects of glucose absorption at different sites (rumen vs. small intestine) on lipid metabolism exhibit significant variation in beef nutrition. This study aimed to investigate the regulatory pathways of rumen-protected or unprotected glucose on lipid metabolism through the rumen-jejunum axis in Xinjiang Brown cattle. Thirty Xinjiang Brown cattle (females) with similar initial weight (410 ± 22.4 kg) were randomly assigned to 3 treatment groups (n = 10 animals per group). The experimental groups were fed a basal diet with the following daily supplements per head: 150 g palmitate coating (CON group), 150 g palmitate coating plus 150 g rumen-unprotected glucose (RUG group), and 300 g rumen-protected glucose (containing 50% glucose; RPG group). The experiment lasted for 70 d. Supplementation with both rumen-unprotected glucose and rumen-protected glucose increased chest width (P = 0.001), chest girth (P = 0.013), abdominal girth (P = 0.002), backfat thickness (P = 0.041), omental fat weight (P = 0.047), as well as serum concentrations of insulin (P < 0.001), glucagon-like peptide-1 (P < 0.001), and 5-hydroxytryptamine (P < 0.001), while decreasing the content of deoxycholic acid (P < 0.001) in the jejunum. The inclusion of rumen-unprotected glucose resulted in a trend toward higher intramuscular fat (IMF) (P = 0.064) in the longissimus thoracis, along with significant increases in C14:0 (P = 0.042), C15:0 (P = 0.014), and marbling score (P = 0.048), as well as significant reductions in drip loss (P = 0.022) and shear force (P = 0.041). These changes were accompanied by significant increases in dry matter intake (P = 0.001), ruminal concentrations of acetate (P = 0.022) and propionate (P = 0.011). The rumen-protected glucose supplementation elevated serum glucose (P < 0.001) level, while enhancing digestibility of ether extract (P = 0.027) and neutral detergent fiber (P = 0.027). Neither rumen-unprotected glucose nor rumen-protected glucose affected the alpha diversity and beta diversity of ruminal and jejunal microbiota (P > 0.05), but the differential bacterial biomarkers were either positively or negatively correlated with chest girth, abdominal girth, marbling score, backfat thickness, and deoxycholic acid (P < 0.05). Rumen-unprotected glucose supplementation enhances IMF deposition and meat quality attributes through microbial volatile fatty acid-driven metabolic reprogramming.