Performance and carcass traits of young Nellore bulls from different residual feed intake classes
This study was carried out to evaluated associations between residual feed intake (RFI), performance and carcass traits of young Nellore bulls feedlot finished. One hundred and twenty-seven Nellore bulls, previously classified as low (n = 63) and high (n = 64) RFI classes, from three selection lines, were evaluated in five different trials. Animals were slaughtered when reached at least 4 mm of subcutaneous fat thickness between 12th and 13th ribs in four trials, and when reached 550 kg of average body weight in the fifth trial. Feedlot performance and carcass traits were measured. Data were analyzed using the MIXED procedure of SAS, including as fixed effects RFI class, selection line, interaction between RFI class and selection line and slaughter age as covariate, and as random effects diet inside trial and trial. Means were compared by t test at 5% of probability. The average difference within RFI classes on dry matter intake was 0.962 kg/day (P < 0.0001), having low RFI animals consumed 0.479 kg/day less than expected and the high RFI ones consumed 0.483 kg/day more than expected. No significant differences were detected between low and high RFI classes, respectively, for slaughter weight (457 and 457 kg; MSE = 12.1 kg; P = 0.9344), empty body weight (418 and 420 kg; MSE = 11.8 kg; P = 0.7685), hot carcass weight (276 and 277 kg; MSE = 8.80 kg; P = 0.7566), cold carcass weight (272 and 272 kg; MSE = 8.86 kg; P = 0.8448), dressing percentage (60.2 and 60.5%; MSE = 0.797%; P = 0.2670), carcass length (124 and 124 cm; MSE = 1.21 cm; P = 0.6624) and carcass depth (40.1 and 40.5 cm; MSE = 0.417 cm; P = 0.2095), demonstrating that low RFI animals, even consuming less food, did not have feedlot performance compromised. Low and high RFI classes also had similar rib eye area (75.7 and 78.4 cm2; MSE = 4.75 cm?; P = 0.1104), rib fat thickness (4.42 and 4.08 mm; MSE = 0.297 mm; P = 0.1905) and rump fat thickness (6.20 and 8.01 mm; MSE = 1.70 mm; P = 0.1738), revealing no phenotypic associations among RFI classes and carcass traits in young Nellore bulls. Animals classified as low RFI presents good feedlot performance and carcass traits, using smaller amounts of feed than animals classified as high RFI.