Tick resistance genetic parameters and its correlations with production traits in Hereford and Braford cattle

Inclusion of cattle genetic resistance to ticks in selection programs represents an auxiliary method in strategic control of this parasite. This study was conducted to estimate genetic parameters for cattle tick resistance measured by tick counting on the inner hind legs region (TCHL) and on one side of body (TCBS) of Hereford and Braford cattle naturally exposed to ticks in southern Brazil. Records of weight gain from birth to weaning (WG), visual scores of conformation, precocity and muscling at weaning (WC, WP and WM, respectively) and at yearling (YC, YP and YM, respectively), weight gain from weaning to yearling (YG) and scrotal circumference (SC) were also analyzed to obtain correlations among all the traits. Heritability estimates obtained by bivariate analysis were TCHL = 0.13 and TCBS = 0.17 and phenotypic correlation between both methods was 0.09 (P<0.05). Repeatability estimate for TCBS was 0.29. Heritability estimates obtained by multivariate analysis were TCBS = 0.19; WG = 0.35; WC = 0.28; WP = 0.23; WM = 0.26; YG = 0.14; YC = 0.18; YP = 0.18; YM = 0.18; and SC = 0.43. No unfavorable genetic correlations among TCBS and growth traits and visual scores at different ages and scrotal circumference have been identified, indicating that simultaneous selection for improving all the traits is feasible.