In Andradina, São Paulo state, the degree of resistance against endo- and ectoparasites was evaluated in heifers from three genetic groups: crossbred Nellore x Aberdeen Angus (Nel x AAn; n=12), Guzerá (Guz; n=22) and Nellore (Nel; n=24). During 12 months, the body weight of each animal was recorded every 28 days as well as the number of Haematobia irritans flies near the animals, and fecal samples were collected to count nematode eggs per gram of feces (EPG). The Nel x AAn group had higher fly counts in comparison with other groups throughout the experiment. There was a significant interaction (P<0.001) between the number of flies and time, and the difference between groups increased over time. The Nel group had lower mean EPG values in four of the twelve experimental months. The animals of the Nel x AAn group had higher average body weight gain since the beginning of the experiment. There was a significant interaction between weight gain and time (P < 0.001) and the difference in weight of the Nel x AAn group increased over time in relation to the Guz and Nel groups. It can be concluded that the crossbred Nel x AAn females presented superior weight gain in relation to the Guz and Nel groups, although they were more affected by Haematobia irritans. In conclusion, the use of crossbred cattle is a good strategy to increase the efficiency of meat production.