ABSTRACTDuring five breeding seasons, 3127 female cattle, sheep, swine and goats in 41 herds in different parts of Bulgaria for pestivirus infection were examined for the possible role of Bovine virus diarrhoea-mucosal disease (BVDV), Border disease (BVD), Classical swine fever (CSF) and for reproductive performance. Before breeding, all animals were investigated for neutralizing antibodies against the four reference strains OREGON C 24, NADL, OSLOSS, ALFORT-187 and one Bulgarian strain—Kableshkovo-76 of pestivirus. The results showed that 198 (6.33%) cattle, 389 (12.44%) heifers, 429 (13.71%) calves, 212 (6.77%) sheep, 318 (10.16%) ewes, 498 (15.92%) lambs, 126 (4.02%) swine, 211 (6.74%) sows, 312 (9.97%) pigs, 183 (5.85%) were positive in 23 herds from different regions of Bulgaria. Antibody titers detected by Virusneutralization reaction (β-procedure) (VNR) and commercials blocking ELISA test-kits (standard test kit/ELISA PPC Sanofi Pasteur; Chekit CST-SERO Suise; Vetoquinol diagnostics Calfcheck BVDV BP 189 70204 Lure Cedex (France) with monoclonal antibody) varied from 1:8 to 1:4096, as in new-borns calves, lambs, pigs, goats the titres ranged from 1:64 to 1:2048. Of 1123 females in 12 herds for which post-breeding information was available, a total 453 (14.48 %) ruminants and swine in 5 of herds demonstrated gestation failure. The heifers, ewes, sows and goats began to produce antibodies against the reference strains OREGON C24, NADL, OSLOSS, ALFORT-187, one Bulgarian strain—Kableshkovo-76 during gestation. The data received from testing of VNR and blocking ELISA test-kits were mathematically calculated by dispersion analyses. The highest geometrical mean titres (GMT) of antibodies were found during pregnancy and new-born calves, lambs, pigs and goats.