Beef quality, liver gluconeogenesis, and muscle lipid metabolism of Nellore steers fed a magnesium oxide blend combined or not with monensin

Dietary magnesium oxide is used to modulate ruminal pH, whereas monensin alters ruminal fermentation, yet their combined effects on beef quality and liver metabolism remain poorly understood. Therefore, this study aimed to evaluate the effects of a magnesium oxide blend and monensin, both independently and in combination, on beef quality, fatty acids profile, liver gluconeogenesis, and muscle lipid metabolism in feedlot steers. Eighty-four Nellore steers were distributed across 28 pens and randomly assigned to the following treatments: CON – a basal diet without additives; MgO – basal diet + magnesium oxide blend; MON – basal diet + monensin; MON+MgO - basal diet + magnesium oxide blend + monensin. The arrangement followed a completely randomized design, structured as a 2 × 2 factorial, where pens were the experimental units. Steers were fed the finishing diet for 100 days. Gene expression analysis was done using the RT-qPCR technique. In the liver, MON+MgO steers tended ( P = 0.06) to upregulate the expression of PCCA compared to MON and CON. In the skeletal muscle at slaughter, monensin-fed steers tended ( P = 0.06) to upregulate the SLC2A4 expression. Steers in CON downregulated ( P = 0.04) ACLY and tended ( P = 0.06) to downregulate ACACA expressions. Steers fed MON had lower ( P = 0.01) oleic acid and monounsaturated fatty acids concentration than CON. Monensin-fed steers exhibited greater concentration of vaccenic ( P < 0.01). Steers fed MgO tended ( P = 0.10) to present lower vaccenic concentration. In conclusion, monensin and magnesium oxide slightly influence lipid metabolism and hepatic gluconeogenesis, resulting in small changes in beef quality.