Performance and lipid metabolism in Nellore x Angus young bulls fed ionophores and non-ionophores

Abstract

The objetive of the currently study was to evaluate the effects of combination between ionophores and non-ionofores additives on performance, carcass traits and lipid turnover over time in feedlot of Nellore  Angus young bulls. Seventy-two animals were utilized, with initial body weight 417.4 ± 41.0 kg, and randomly allotted in 18 pens, totalizing 4 animals per pen, in a completely randomized design. The three treatments consisted of supplementation of monensin (MON), monensin plus zinc bacitracin (MONZB) or monensin plus virginiamycin (MONVM). Monensin, zinc bacitracin and virginiamycin doses were 25.0, 8.75 and 25.0 mg/kg dry matter, respectively. The facilities and diet adaptation period lasted 27 d and the experimental period 82 d. The diet consisted in 15% of corn silage and 85% of concentrate. It was performed muscle biopsy from longissimus thoracis on d 7 of the experimental period to RT-qPCR analysis. In addition, blood samples were collected on d 7 and 43 of the experimental period to measured serum D-lactate concentration. At slaughter were collected muscle samples. There was no significant effect on overall performance, feed efficiency and most of carcass traits (P > 0.16). Animals fed MONVM presented lower average daily gain (ADG) in the beginning of the feedlot (P = 0.02). On the other hand, in the end of the feedlot the same treatment presented greater ADG (P = 0.08). Serum D-lactate concentration was similar among the three treatments and was not affected by time (P > 0.40). Animals fed MONVM had higher number of meals compared to animals fed MON (P = 0.03). On the other hand, animals fed MON had greater preferential intake of middle particle size (8 to 19 mm) than animals fed MONVM (P = 0.05). While animals fed MON, also refuse more the small particles (< 8 mm) than other treatments (P < 0.01). The expression of SREBF1, PPARG, ACACA and SCD1 was not influenced by the additives either by time (P > 0.20). However, the expression of LPL and CD36 increased over time (P = 0.02), while FASN expression decreased (P = 0.07). MONZB presented greater expression of PPARA on d 7 and lower expression at slaughter (P = 0.07). CPT2 expression was lower on d 7 for MONZB and higher for MONVM at slaughter (P = 0.07). Thus, the alone or combined use of the additives did not improved animal overall performance either carcass traits, suggesting that additives can be used alone or combined. In addition, the changes in gene expression was not enough to modify chemical composition of the meat.