The effect of tick infestations on liveweight gain (LWG) was assessed by comparison of weight changes in flumethrin-treated N'Dama and Gobra zebu cattle (16-20 months old) with respective control groups submitted to natural tick challenge over 1 year. Flumethrin was applied monthly, fortnightly or weekly. Preventive treatments against anaplasmosis, babesiosis and trypanosomosis were given. Mortality rate was recorded and post-mortem examinations carried out. In both treated and control animals, significantly fewer Hyalomma spp. and Amblyomma variegatum were found on N'Dama than on Gobra zebu cattle. Both breeds are equally susceptible to Rhipicephalus senegalensis infestation. Total annual tick burdens did not cause significant differences in LWG between acaricide-treated and control cattle in either breeds. LWG was also not affected during or after the annual peak of tick infestation (composed mainly by A. variegatum and R. senegalensis). Equally-high mortality (35%), due to unidentified causes, was recorded in acaricide-treated and control Gobra cattle; mortality in N'Dama cattle was 7.5%. In both breeds, about the 90% of mortality occurred at the end of the dry season. Breed differences in tick burden confirm previous results. If tick-borne infections do not influence LWG or mortality, then it is concluded that intensive tick control is not justifiable in Gambian livestock.