The aim of this work was to know the biological impact of wastewaters on livestock in the localities of Dladla and Boukallou (Town of Settat, Morocco), where wastewaters are largely used by the local population for their agricultural activities. We used the micronucleus (MN) test in cytochalasin B blocked binucleated cells (BNC) to assess the possible induced genetic effects. The cellular proliferation index (PI) was also calculated. Blood samples were collected from sheep, bovines and mules and peripheral blood cultures were made according to our laboratories' standard methodology. The results showed a significant increase of micronucleated cells in the lymphocytes of the exposed animals (14+/-8.79 MN/500 BNC) compared to the control (3+/-1.54 MN/500 BNC). The PI showed a nonsignificant decrease in the exposed animals. The highest MN frequency was found in mules which is probably due to their more sedentary life. Direct use of the wastewater by the animals as their source of drinking water significantly increased the frequency of cells with micronuclei. We also established an inverse correlation between the chromosome number and the PI. These results suggest a serious degradation of the ecosystem due to the wastewaters with a direct impact on its inhabitants.