| Abstract: | This study was designed to estimate dietary energy level on intramuscular fat (IMF) deposition in Simmental × Yellow breed cattle. Results showed that ultimate weight and average daily gain in high and medium energy groups were significantly higher than low‐energy group, yet feed conversion ratio was significantly lower. IMF content was significantly increased by dietary energy increasing, whereas longissimus muscle shear force significantly decreased. Serum‐free fatty acids, triglycerides and glucose significantly increased by dietary energy increasing, whereas growth hormone (GH) significantly decreased. Enzyme activities of lipoprotein lipase (LPL), fatty acid synthase (FAS), and acetyl‐CoA carboxylase (ACC) significantly increased by dietary energy increasing, whereas hormone‐sensitive lipase (HSL) and carnitine palmitoyltransferase‐1 (CPT‐1) significantly diminished. Peroxisome proliferator‐activated receptor γ, sterol regulatory element‐binding protein 1, stearoyl‐CoA desaturase, adipocyte‐fatty acid‐binding proteins, ACC, LPL, and FAS gene or protein expression significantly increased by dietary energy increasing, whereas HSL, CPT‐1, and GH gene or protein expression significantly decreased. These results indicated that high dietary energy promoting IMF deposition is mainly by downregulating pituitary GH gene expression, decreasing serum GH concentration, increasing lipogenic genes levels of mRNA, enzyme activities and protein expression, and decreasing lipolytic genes levels of mRNA, enzyme activities, and protein expression. |
