Estimativas de herdabilidade e repetibilidade do grau de infestação por ectoparasitos em fêmeas de quatro grupos genéticos de Bovinos de Corte.

Abstract

The objective of this study was to estimate heritability and repeatability of the degree of infestation on females of four beef cattle genetic groups by external parasites, in order to evaluate the possibility of selection to increase resistance to parasitism. Cattle tick (“Boophilus microplus”), horn fly (“Haematobia irritans”) and beef-worm (“Dermatobia hominis”) countings on Nellore (NE), Angus x Nellore (AN), Canchim (5/8 Charolais + 3/8 Zebu) x Nellore (CN) and Simmental x Nellore (SN) naturally infested females, were carried out, from July 2003 to December 2004, for one to ten times, on 708 animals of several physiological states. Estimates of genetic parameters were obtained by the restricted maximum likelihood method, using models that included fixed effects of genetic group, year-season of counting and physiological state, and additive direct and animal’s permanent environmental random effects. Data were transformed to log10 (n + 1) for statistical analyses. Heritability and repeatability estimates were 0.15 and 0.15, 0.24 and 0.28, and 0.06 and 0.10, for number of cattle ticks, horn flies and beef-worms, respectively, indicating that it is feasible to obtain genetic progress for horn fly resistance, selecting low infested females of these genetic groups.