Catalyzes the deamination of cytidine and deoxycytidine into uridine and deoxyuridine, respectively (PubMed:26945630). May play an important role in testicular development and spermatogenesis (PubMed:16955368). 2'-deoxycytidine + H(+) + H2O = 2'-deoxyuridine + NH4(+) cytidine + H(+) + H2O = NH4(+) + uridine Widely expressed. Expressed at high levels in the testis. Belongs to the cytidine and deoxycytidylate deaminase family.