Evaluation of disposition scores in Bos indicus/Bos taurus cross calves at different stages of production

Aggressiveness, nervousness, flightiness, gregariousness and overall disposition were evaluated in F2 Nellore-Angus embryo transfer calves (n = 443) from 13 full sib families and in half Bos indicus, half Bos taurus natural service calves (n = 259) from 4 paternal half sib families. Calves were born from 2003 to 2007, and evaluated shortly after weaning. Steers were evaluated shortly before slaughter for all 5 disposition traits and at slaughter for overall disposition. Heifers were evaluated for overall disposition at calving every year. Scores ranged from 1 to 9, with 1 being docile and 9 being unruly, except at calving where scores ranged from 1 to 5. Between sires for overall disposition, calves by 297J were lowest at weaning (2.83), before slaughter (2.84), and at slaughter (2.45) and second lowest in first calf heifers (2.27). Calves by 437J were highest at weaning (4.10), before slaughter (3.54), at slaughter (2.89) and in first calf heifers (3.10). Bulls had the lowest scores at weaning (2.54), although the number was small (n=10); females were the highest (4.01), and steers were intermediate (3.70). All 5 weaning traits were correlated (P < 0.05) with each other (0.73 to 0.96). The correlation of recipient disposition and weaning disposition of the calves was 0.12 (P < 0.05). Aggressiveness was not significantly correlated with other component traits before slaughter but was with overall disposition (0.19, P < 0.05). All other traits were significantly inter-correlated (0.60 to 0.97). Disposition at weaning was correlated with disposition before slaughter (0.43, P < 0.05). Slaughter disposition was correlated with weaning disposition (0.30, P < 0.001) and disposition before slaughter (0.27, P < 0.001). Disposition in first calf heifers was correlated with weaning disposition (0.34, P < 0.001) and disposition in second calf females (0.53, P < 0.0001). The results indicate that both genetics and recipient disposition affect calf disposition at weaning, calves with better dispositions at weaning have better dispositions later in life, and there is sufficient variability within and between these full sib and half sib families for use in QTL analysis for major genes for disposition in Nellore-Angus cross cattle.