PSV-27 Expression of genes involved in lipid metabolism and gluconeogenesis of Nellore steers fed a magnesium oxide blend combined or not with monensin.

Abstract The objectives of the study were to evaluate the expression of genes related to lipid metabolism in skeletal muscle and liver gluconeogenesis in Nellore steers fed a magnesium oxide blend combined or not with monensin. Eighty-four Nellore steers (367.3 ± 37.89 kg) were used in a completely randomized design. Animals were stratified by body weight, housed in 28 pens (3 animals/pen and 7 pens/treatment), and assigned to one of the four treatments. The treatments were: control (CON) – steers fed a basal diet without any dietary additive; magnesium oxide blend (MgO) – the basal diet supplemented with a magnesium oxide blend (pHix-up®, Timab Magnesium, Dinard, France) included at a level of 0.50 % of dry matter (dry matter); monensin (MON) - the basal diet supplemented with 25 mg/kg of DM of sodium monensin (Rumensin, Elanco Animal Health, Greenfield, IN); and MgO combined with MON (MgO + MON). Animals were fed a basal finishing diet (77.8 % total digestible nutrients, and 13.3 % crude protein) for 100 days. At 70 d on feed, biopsy samples were collected in the longissimus thoracis (LT) muscle and liver. After the feeding period, animals were slaughtered in a commercial abattoir and samples were again collected in the LT muscle. All tissue samples were immediately frozen in liquid nitrogen, then stored at -80 ºC until further analysis. Gene expression was assessed using RT-qPCR technique. Data were analyzed using the MIXED procedure of SAS 9.4 with fixed effects of dietary treatment and random effects of pen nested within treatment. No treatment differences were observed (P > 0.11) in the PC, LDHA, and PCK1 expressions in the liver at 70 d on feed. However, PCCA expression tended to be upregulated (P = 0.06) in MgO steers than in CON and MON steers. In the LT muscle at 70 d on feed, treatments did not affect (P > 0.11) ACACA, CPT1A, PPARA, and ACLY expressions. The SLC2A4 expression was downregulated (P = 0.04) in steers fed MON, MgO, or MgO + MON in comparison to CON animals. Thus, MgO + MON steers upregulated (P = 0.05) the SREBF1 expression compared to MON and MgO. At slaughter, no differences were observed (P > 0.12) in CPT1A, PPARA, and SREBF1 expressions. On the other hand, SLC2A4 expression tended to be upregulated (P = 0.06) in MON and MgO + MON compared to CON steers. In addition, the expressions of ACACA tended to be downregulated (P = 0.06) and ACLY was downregulated (P = 0.04) in CON steers compared to other treatments. In summary, under the conditions of the present study, the additives inclusion and its combination were capable of slightly modify the expression of genes related to gluconeogenesis and lipid metabolism.