Expression of genes related to the regulation of muscle protein turnover in Angus and Nellore bulls

Abstract

We aimed to evaluate the expression of genes related to the regulation of muscle protein turnover in the longissimus dorsi (LD) muscle of Angus and Nellore bulls and to estimate the within-breed correlations of gene expression and performance traits. Thirteen genes related to the IGF-1 and myostatin pathways were studied. Thirteen animals, with an initial average BW of 381.2 ± 11.8 kg, from each breed were used in a completely randomized 2 × 2 factorial design (2 breeds and 2 feeding levels). The diet consisted of corn silage and a corn–soybean meal concentrate in a roughage-to-concentrate ratio of 30:70. Cattle were fed ad libitum (with 9 animals from each breed) or feed restricted (a 55% restriction of total DMI of ad libitum–fed animals, calculated as percentage of metabolic BW, with 4 animals of each breed). The experimental period lasted for 82 d and it was preceded by a 28-d adaptation period. The performance traits evaluated were slaughter body weight, total ADG (from d 1 to 82 of the trial), initial ADG (from d 1 to 41 of the trial), final ADG (from d 42 to 82 of the trial), total DMI (from d 1 to 82 of the trial), initial DMI (from d 1 to 41 of the trial), final DMI (from d 42 to 82 of the trial), HCW, LD weight (LDW), and rib eye area (REA). After slaughter, samples were taken from the LD muscle between the 12th and 13th ribs for gene expression analysis by quantitative reverse transcription PCR. There was no difference (P > 0.05) in the expression of any of the genes studied between ad libitum–fed Angus and ad libitum–fed Nellore, whereas feed restriction increased the expression of IGF-1 receptor (IGF1R; P < 0.001), muscle ring finger 1 (MuRF1; P = 0.05), and mothers against decapentaplegic homolog 3 (Smad3; P = 0.04) and decreased the expression of IGFBP5 (P < 0.01). The REA was negatively correlated to glycogen synthase kinase 3β (GSK3β; P = 0.01), myostatin (MSTN; P = 0.02), and MuRF1 (P = 0.05). The HCW was negatively correlated to GSK3β (P = 0.01) and MSTN (P = 0.01) and tended to be negatively correlated to IGFBP5 (P = 0.07), whereas the LDW tended to be negatively correlated to GSK3β (P = 0.08). The genes MuRF1, Smad3, and IGFBP5 seem to be important for muscle growth and may be worthy of further investigation as future strategies for increasing muscle in livestock.