The effect of spraying for buffalo fly (Haematobia irritans exigua) on infestations, growth rate and lesion development on Bos indicus × B. taurus cattle in the dry tropics of north Queensland

摘要

The effect of spraying for buffalo fly (Haematobia irritans exigua) on infestations, growth rate and lesion ndevelopment on Bos indicus x B. taurus steers (18 months old) and bullocks (30 months old) were nstudied in the dry tropics of North Queensland. There were four consecutive drafts commencing between nJuly and September and terminating the following June-July. Half of the animals were sprayed with n200 g/l fenvalerate to control buffalo flies. nTreated animals carried, at most, a few flies. The size of the fly populations on the untreated animals nvaried with the seasons, with the most flies being recorded during the wet season. Light coloured animals ncarried fewer flies than those with darker colours and bullocks carried more flies than steers. Except for nsteers in one dry season, repeatabilities of fly counts were significant (P < 0.01). In steers, treatment nhad no significant (P > 0.05) effect on growth over the four treatment periods, although there were nsignificant effects of treatment on growth in some intermediate periods. Treatment significantly n(P < 0.05) affected bullock growth in two of the four years. Significant (P < 0.05) positive correlations nwere found between fly counts and growth rate in two years. nFew lesions were recorded on treated animals. Lesion prevalence and size on untreated animals were ngenerally not associated with fly counts, coat colour or growth rate.