Chemical composition and expression of genes involved in lipid metabolism in the muscle of Nellore and Angus young bulls fed whole shelled corn diet

Abstract Text: The objective was to evaluate expression of genes involved in lipid metabolism and chemical composition of longissimus dorsi (LD) muscle of Nellore and Angus bulls fed whole shelled corn (WSC) and a ground corn (GC) diet. Twenty-eight bulls with average initial body weight of 378 ±8.7 kg were used in a completely randomized design and arranged as a 2 × 2 factorial (2 breeds and 2 diets). The GC diet had 30% of corn silage and 70% of a concentrate based on corn and soybean meal. The WSC diet had 85% whole shelled corn and 15% of a pellet based on soybean meal and minerals. After harvested, samples were taken from the LD muscle between the 12th and 13th ribs for centesimal composition analyses and gene expression, which was analyzed by RT-qPCR. The model included the fixed effects of breed, diet, and their interaction. Expression of PPARA was greater in LD of Nellore bulls (Table 1; P < 0.01). In addition, PPARA was more expressed when bulls fed WSC diet (P = 0.04). Opposite results were found for SREBF1 expression, which was less expressed when bulls fed WSC diet (P < 0.01) and in Nellore (P = 0.03). PPARG and carnitine palmitoyl transferase 2 (CPT2) expression was downregulated in the LD muscle of Nellore bulls fed WSC and up regulated in LD of Angus fed the same diet. Expression of lipoprotein lipase (LPL), fatty acid binding protein 4 (FABP4), acetyl CoA carboxylase (ACACA) and stearoyl-CoA desaturase (SCD1) was greater (P < 0.05) in the LD of Nellore bulls fed GC diet. However, diets did not affect the expression of these genes in the LD muscle of Angus bulls. Fatty acid synthase (FASN) expression was greater in the LD of Nellore bulls (P < 0.01) and when animals fed WSC (P < 0.01). Expression of acyl-coenzyme A oxidase 1 (ACOX) was greater for Angus fed WSC (P = 0.04). Meat from Angus bulls had greater intramuscular fat than Nellore (4.95 and 4.30; P = 0.05). However, there was no effect (P > 0.05) of diet on intramuscular fat. Moisture and protein were not affected (P > 0.05) by diet and breed. In conclusion, expression of PPARA and SREBF1 have opposite regulation mechanisms in bovine muscle, regardless the subspecie. Diets affected expression of some genes involved in lipid metabolism differently in Nellore or Angus bulls.

Keywords: lipogenesis, marbling, PPAR, SREBF1, transcription factor