The study examined the possibility to identify individual differences in behaviour of Nellore cattle and the implications in meat quality traits. A total de 76 Nellore cattle, aged 24 month were observed. The reactivity of the animals were evaluated by breathing, (1=imperceptible, 2=rhythmic perceptible, 3=perceptible with gasp), locomotion in the balance (1=stopped, 2=slow locomotion, 3 = fast locomotion) and flight speed (1=stagnant, 2=slow speed, 2=fast speed). After slaughter, carcass pH at 1 and 24 hours was measured. Following, three Longissimus dorsi muscle samples of 2.5 cm thickness were collected from between 12th and 13th ribs for analysis of tenderness at 1st, 7th and 14th days post mortem. Statistical analysis were performed utilized the MIXED procedure of SAS, considering a model with pH (1h and 24h), Warner Bratzler Shear Forces, at 1st, 7th and 14th days post mortem as dependent variables and sexual condition (C=intact and castrated) and the reactivity traits as independent variables. The means and standard deviations for pH at 1 and 24 hours were 6.68 ± 0.17, 5.57 ± 0.16, respectively. For meat tenderness at 1st, 7th and 14th days post mortem were 8.76 ± 1.66, 7.70 ± 1.39, 6.43 ± 1.16 kgf, respectively. Analysis demonstrated that there were not significant effects for breathing and locomotion. However were observed significant effect for flight speed influenced in meat tenderness at 7 days (P＜0.07) and 14 days (P<0,10). The inclusion of neuroendocrine traits will help to elucidate the biological mechanisms involved individual differences in reactivity.
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