Resumen

MELENDEZ, Roy D. et al. Levels of natural resistance to Boophilus microplus (Acari: Ixodidae) in Carora breed bulls. Rev. biol. trop [online]. 1998, vol.46, n.3, pp.691-696. ISSN 0034-7744.

Boophilus microplus infestation is one of the most serious limitations to cattle industry in tropical regions, even though bovines show natural resistance to ticks. This resistance was evaluated in Cross-bred Carora Bulls (CCB) a tropicalized dairy breed from Venezuela. Seven CCB were experimentally infested with B. microplus larvae, "Mozo" strain, they were considered tick-naive because they had never been infested with ticks. The mean inoculum size applied on each bull was 6 477 larvae. After life cycle was completed adult female body weight (BW), egg mass weight (EW), egg hatching rate (%EH), and reproductive index (RI) were recorded. Results revealed a high variability in the levels of resistance to B. microplus. Thus, one animal showed greater resistance (Dunnett, p< 0.05) for the analyzed parameters in contrast with three non-resistant bulls. The others had moderate resistance. The trait "resistance" should be included togheter with other traits often used in genetic selection of cattle.

Palabras clave : Boophilus microplus; Carora breed cattle; resistance to ticks; natural resistance.