Differential lipid metabolism in beef cattle: A comparative study of high and low residual feed intake bulls

This study investigated lipid metabolism differences between low and high residual feed intake (LRFI and HRFI) bulls. Fifty-five Simmental bulls (449.84 ± 8.49 kg) were fed the same diet for 161 d to determine RFI values. At the end of experiment, back fat thickness (BFT) and rib eye area (REA) were measured via ultrasound, and serum samples were collected for lipid metabolism indicators. Post-slaughter, subcutaneous adipose tissue was analyzed for lipid metabolism indicators, histology, transcriptomics, and lipid metabolomics. Results 1) Ultrasound showed LRFI bulls had lower BFT (P = 0.031) but higher REA (P = 0.021). 2) Serum total cholesterol (P = 0.028) and low-density lipoprotein cholesterol (P = 0.015) were lower in LRFI bulls. Leptin levels were lower in both serum (P = 0.007) and adipose tissue (P = 0.001) in LRFI bulls, as were acetyl-CoA carboxylase levels in serum (P = 0.032) and adipose tissue (P = 0.043). Conversely, adipose triglyceride lipase levels were higher in both serum (P = 0.045) and adipose tissue (P = 0.043), while adipose tissue fatty acid synthase levels were lower (P = 0.035) in LRFI bulls. 3) Transcriptomics identified two pathways, adenosine monophosphate-activated protein kinase (AMPK) and cyclic adenosine monophosphate (cAMP), involving five lipid metabolism-related genes. Among these, adenylate cyclase activating polypeptide 1 receptor type 1 (ADCYAP1R1), adenylate cyclase 10 (ADCY10), and adenylate cyclase activating polypeptide 1 (ADCYAP1) were significantly upregulated (P < 0.05), while leptin receptor (LEPR) was downregulated (P = 0.047) in LRFI bulls. Additionally, leptin (LEP) showed a downward trend (P = 0.098) in LRFI bulls. 4) Lipid metabolomics revealed that the LRFI group had significantly higher levels of wax ester (WE) (P = 0.040) and significantly lower levels of monogalactosyldiacylglycerol (MGDG) (P = 0.040) compared to the HRFI group. Additionally, sphingomyelin (SPH) showed a trend towards lower abundance (P = 0.054), and C12:0 levels tended to be higher (P = 0.089) in the LRFI group. In conclusion, differences in the AMPK and cAMP signaling in adipose tissue are associated with reduced lipid synthesis and enhanced lipid degradation in LRFI bulls, which may contribute to reduced lipid deposition.