Effect of replacing antibiotics with functional oils following an abrupt transition to high-concentrate diets on performance and carcass traits of Nellore cattle

The aim of this study was to investigate the effects of different feed additives on performance, feeding behavior, blood metabolites, carcass traits and meat quality of finished Nellore cattle in feedlot, with abrupt transition to high-concentrate diets. Forty-eight 20-mo-old Nellore bulls {[}initial body weight (BW) of 322 +/- 33 kg] were distributed in a complete randomized design and fed with a basal diet containing different additives: 30 mg/kg dry matter (DM) of monensin (M30), 40 mg/kg DM of monensin (M40), 30 mg of monensin +25 mg of Virginiamycin/kg DM (MV), and 400 mg/kg DM of Functional oils (FO; castor oil and cashew nut shell liquid). Animals were fed a diet of 92% concentrate on the first day of feedlot. Dry matter intake (DMI), body weight (BW) and blood parameters were evaluated at days 1, 7, 14 and 21 (transition period), then every 21 days to analyze performance and ultrasound carcass traits until slaughter. Animals fed FO had a greater DMI then MV (P = 0.002) in the transition period, and showed no differences for M30 and M40, as well as for blood metabolites. In the feedlot period (120 days), the DMI was greater in FO then in M30 and in MV (P < 0.05) with no differences from M40. The ADG, G:F and final BW, rumen parameters, carcass traits and meat quality showed no differences. However, the MV treatment had higher concentration of 15:0 and 17:0, 17:1, 18:1 t10, t11, t12 and 18:2, t10, c12 fatty acids. In conclusion, the abrupt transition of a diet to high concentrate did not affect performance and blood parameters. The FO did not affect negatively the performance, carcass traits and meat quality, compared to Nellore cattle in feedlot fed conventional additives. (AU)