Temperament effects on performance and adaptability of Nellore young bulls to the feedlot environment

The aim of this study was to evaluate the effects of temperament on cattle performance and adaptability to the feedlot environment. Temperament of 1,350 Nellore young bulls (pure and crossbred) were assessed by the flight speed (FS) test on days 0 (FS0), 35 (FS35) and 87 (FSfin) in the feedlot, and the differences between FSfin and FS0 (ΔFS) were calculated. Three classes of flight speed were defined (calm, intermediate and reactive) for FS0 (FSC0) and FSfin (FSCfin). Performance was assessed by recording body weights on days 0, 35 and 87 (BW0, BW35 and BWfin, respectively), average daily gains between days 0 and 35, and 0 and 87 (ADG0-35 and ADG0-fin, respectively), and hot carcass weight (HCW). Adrenal glands of a subset of 270 animals were collected to measure their weight (WEIGHT), and cortical (COA) and medullary (MEA) areas. Spearman's coefficients of correlation were estimated to assess the relationships between FS test results over time. General linear mixed model with Proc MIXED of SAS was used in all other analyses, and a repeated measures modelling was used for FS, except for ΔFS. For FS the model included the fixed effects of space allowance, days in feedlot and 2-way interaction. For ΔFS analysis only space allowance was included. Performance and adrenal gland variables were analyzed considering the fixed effects of space allowance, flight speed classes (for FSC0 and FSCfin, separately) and 2-way interaction in the model. BW0 was fitted as a covariate in the all models. Means comparisons between FS classes were corrected by Tukey adjustment. Significant and positive correlations were found between all FS test results, which decreased over time   in all feedlot space allowances (p<0.01). Calm animals showed higher (p<0.05) ADG0-35, BW35 and BWfin means    than intermediate and reactive ones, and at the end of the finishing period these animals also produced heavier carcasses (p < 0.05). A significant effect of the interaction between FSCfin and space allowance was found for ADG0-fin, showing that reactive cattle have lower performance when kept in lower space allowance in feedlot. Reactive cattle (FSC0) had greater COA and heavier WEIGHT than calm and intermediate ones. Based on these results, we conclude that calm animals show better performance in feedlot, regardless of the space allowance in the pens; probably because the reactive ones face more difficulties to adapt to the feedlot conditions, suffering with chronic stress.