Desempenho, qualidade da carne e expressão de genes envolvidos no metabolismo lipídico de novilhos nelore recebendo monensina e/ou óxido de magnésio

Abstract

The inclusion of additives in cattle confinement diets has been a strategy to improve performance through mechanisms related to the control of rumen acidosis. A source of MgO was developed to have a high effect on ruminal pH. This experiment evaluated the effect of a blend of different sources of magnesium oxide associated or not with monensin on performance, carcass characteristics, meat quality, expression of genes involved in the regulation of protein turnover and lipid metabolism. Eighty-four castrated Nelore steers with 367.3 ± 37.9 kg of initial body weight were distributed in a completely randomized design in a 2 × 2 factorial scheme with the following treatments: CON – without additives; MG - pHixUp® at 0.50% dry matter (DM) and 0% sodium monensin; MON - monensin up to 20 mg/kg and 0% pHix-Up®; and MON+MG - the combination of monensin × pHix-Up®. During the experimental period (100 days), the animals received a basal diet containing 20% neutral detergent insoluble fiber (NDF) and 52.5% starch. Body weight was recorded on days 0, 13, 39, 70 and 100 for performance measures. Blood samples were collected on days 0, 13 and 70 for D-Lactate analysis. On day 70, liver and muscle biopsies (Longissimus thoracis) were performed from one animal per pen for gene expression analysis. Cattle slaughtered in a commercial slaughterhouse and muscle and rumen epithelium samples were collected for gene expression and histology analysis, respectively. In addition, meat samples (Longissimus thoracis) were collected for qualitative analysis. No effect of the MON+MG treatment was detected (P ≥ 0.22) for performance, carcass characteristics, feeding behavior, pH, color and cooking losses. However, this treatment increased the concentrations of C18:1c9 and monounsaturated fatty acids and tended to increase the tenderness of the meat. MG increased (P < 0.01) DM intake (CMS), average daily gain (ADG), expression of the Propionyl-CoA Carboxylase Alpha Subunit (PCCA) gene, D-lactate concentration and tended to increase hot carcass weight as well as thawing losses. There were no effects of treatments (P ≥ 0.10) on the ruminal epithelium. MON increased feed efficiency and selection of long particles, but without effect on DMI, ADG and meat quality. In conclusion, the inclusion of MG improves the performance of steers in feedlot diets with high starch content, but MG associated with MON tends to improve the qualitative characteristics of the steers' meat.