The aim of this study was to assess the effect of temperament on feedlot performance and carcass traits in Nellore and crossbred cattle (F₁ Angus × Nellore and Caracu × Nellore). A total of 450 bulls raised on pasture and finished in feedlot were kept in outdoor feedlot pens with 12 m², during 87 d of confinement. Cattle temperament was assessed using the crush test (REA, recording the movements and tension inside the crush in a 7-point scale); and the flight speed test (FS, m/s), measuring the speed at which the animals exited the crush, measured in the beginning (d 0, initial) and in the end of the feedlot period (final). Performance and carcass traits used were: final BW, ADG, hot carcass weight (HCW), carcass yielding (CY), subcutaneous fat score (SFS), number of bruises in the carcass (BRU) and ultimate meat pH (pH_24h). Linear mixed models were fitted to assess the effects FS and REA on dependent traits. Final FS affected (P < 0.05) BW and ADG, with an estimated reduction of 7.92 kg in BW and 0.13 kg/d in ADG for an additional unity in FS (Table 1). Final FS had significant effects on most of the carcass traits assessed, resulting in reduction of CW (P < 0.05), SFS (P < 0.01), and increased BRU (P < 0.05) and meat pH_24h (P > 0.05). Final REA affected only CY (P < 0.05). Initial FS and REA had less pronounced effects on performance traits, with initial FS effecting only BRU (P < 0.01), and initial REA affecting ADG (P < 0.05). We conclude that more excitable temperament (faster FS) may have negative effects on cattle feedlot performance, carcass traits and meat pH_24h. The FS assessed at the end of feedlot period was the best predictor of the detrimental effects of temperament on performance of Nellore and crossed cattle. Financial support: FAPESP (2013/20036–0). Table 1. Effects of initial and final flight speed (FS) and reactivity score (REA) on feedlot performance and carcass traits, expressed as regression slopes (β)

Trait	β FS initial	β REA initial	β FS final	β REA final
Final BW, kg	−4.58	−1.12	−7.92*	−0.91
ADG, kg/d	0.00	−0.05*	−0.13*	0.00
Carcass weight, kg	−1.70	−0.31	−6.23*	−1.52
Carcass yielding, %	0.23	−0.12	−0.10	−0.28*
Subcutaneous fat score	−0.29	−0.02	−0.66†	0.07
Bruises	0.25†	−0.01	0.22*	0.02
pH24h	0.00	0.00	0.02*	0.00

*P < 0.05; †P < 0.01.