PSVII-19 Effects of silage particle size on beef quality and muscle lipogenesis of finishing Nellore heifers

Abstract The objective of this study was to evaluate the effect of corn silage particle size on beef quality and expression of gluconeogenic and lipogenic genes in feedlot-finished Nellore heifers. Nellore heifers (n = 94), with an initial body weight (BW) of 249.71 ± 34.62, were allotted into 32 pens (three animals per pen) in a completely randomized design, with 2 treatments and 16 repetitions. The treatments were corn silage with a particle size of 13 mm (short) or 24 mm (long). The feeding period lasted 101 d, with the first 15 d for diet adaptation. After slaughter, samples of the longissimus thoracis muscle (LT) from the left side of the half carcass and liver were taken for beef quality and gene expression analyses. The chemical composition of the beef was analyzed using near infrared according to the AOAC method 2007-04, using the FoodScanTM equipment (AOAC method: 2007-04; FOSS, Hillerod, Denmark). RT-qPCR analyses of each gene investigated were carried out using cDNA from 16 biological replicates per treatment (1 heifer chosen randomly in each pen), with each biological replicate subjected to 2 technical replicates. Relative gene expression analyses were calculated using the delta delta ct method and the reference genes used were ACTB and GAPDH. The normality of all experimental data was checked using the Shapiro-Wilk test in SAS software. When the data did not present a normal distribution, transformation was performed using PROC RANK. The model included particle size as a fixed effect and pen as a random effect. There was no treatment effect on collagen, moisture, and mineral content (P > 0.10), but muscles from heifers fed short particle sizes tended to have greater protein content (23.3 versus 22.9; P = 0.098), while muscles from heifers fed with long particles had greater intramuscular fat content (2.62 versus 3.28; P = 0.05). For liver gene expression, heifers fed short particle sizes tended to have greater expression of the PC gene (1.00 versus 0.82; P = 0.06), while PEPCK2 had higher expression in heifers fed long particles (1.00 versus 1.18; P = 0.04). In addition, the long particle size of corn silage affected the expression of PPARA (P = 0.001), and there was no effect of diets (P > 0.05) on PPARG and SREBF1 expressions (Table 1). Expression of LPL, FABP4, SCD1, CPT2 (P < 0.001), and ACACA (P = 0.017) genes increased in the muscle of heifers fed long particle size. Therefore, it is concluded that the use of corn silage with long particle size in feedlot diets has the potential to increase the expression of genes involved in lipogenesis and then increase intramuscular fat in Nellore heifers.