Abstract:
The dynamics of host resistance to Boophilus microplus was investigated in previously unexposed and exposed Brahmans, and in previously unexposed Shorthorn cattle. The animals were infested each day with 1000 larvae, and the development of resistance was monitored by counting the number of female ticks which engorged. The previously unexposed cattle showed an initial period of susceptibility (phase I) which was followed by a period in which most animals developed degrees of resistance (phase II), and which stabilized in some animals (phase III). The duration of phase I was shorter in Brahmans, and they developed higher levels of resistance (phase III). In contrast, previously cxposed Brahmans manifested phase III levels of resistance immediately on infestation. The results provide further evidence that resistance to B. microplus in Brahmans, as well as in European breeds, is acquired rather than innate. __________________ *Part I, Aust. J. Agric. Res., 26: 1073 (1975).