Bovine viral diarrhoea (BVD) is a worldwide viral cattle disease. Percentage of seropositive animals, especially in the countries with intensive cattle breeding ranges from 60-90%. This infection on our epizootiology area, as well as on area in our surrounding, was for the first time described by OEuriåkoviñ et al. (1966) based on clinical pictures and pathomorphological findings. This was proved by antibody detection by Cvetnić et al. (1968). In the last few years a large number of serology examination was done on the presence of BVDV infection in our area. In 2004 an examination on virus neutralisation antibodies in sera of breeding dairy cattle older than 6 months was carried for the purpose of determining the prevalence of BVDV infection in large and small herds in Southern Bačka and Srem districts. There were 7577 sera samples from small herds, out of which 3457 were from Southern Bačka (26.31% out of total population in all 9 municipalities), and there were 4120 samples from Srem district (25.17% out of total population in all 8 municipalities). The examination included the animals from all settlements (156). From large cattle herds there were 3019 sera samples, out of which 2721 were from 18 large farms in Southern Baåka (38.65% out of total population), and 298 from 4 large farms in Srem district (29.22% out of total population). This examination encompassed animals from 22 large farms on this area. Virus neutralisation test (VN) was carried out according to the standard procedure described in ’’Manual of Diagnostic Tests and Vaccines for Terrestrial Animals’’ Office International des Epizooties (2004) with slight modifications. For test NADL strain of BVD virus and MDBK cell culture were used. The sera were examined in double dilution from 1:2 to 1:512. Virus neutralisation antibodies for NADL strain BVDV were detected in 1833 (24.19%) in the samples from small herds. Out of this number there were 1082 (31.30%) seropositive animals from Southern Baåka and 751 (18.53%) from Srem district. The largest number of seropositive animals in Southern Baåka district were detected in Titel municipality (68.07%) and the lowest in Bački Petrovac municipality (6.63%). In Srem district the largest number of seropositive animals was in Beoåin municipality (34.16%) and the lowest in Irig municipality (7.62%). When comparing all the settlements, the percentage of BVDV seropositive animals ranged from 0% (i.e. settlements with no seropositive animals) up to 86.67% (Krnjeãevci). Virus neutralisation antibodies for BVDV NADL strain were detected in 1667 (55.22%) samples from large cattle herds. Out of this number there were 1500 (55.13%) seropositive animals from Southern Bačka, and 167 (56.04%) seropositive animals from Srem district. The prevalence of seropositive animals in large herds from Southern Baåka district ranged from0%(5 large herds) up to 96.61%. High prevalence (70%) was detected in 7 out of 18 examined herds. The prevalence of seropositive animals originating from large herds in Srem district ranged from 0% (1 large herd) to 96.96%. High prevalence (70%) was detected in 2 out of 4 examined herds. Detected variation in the percentage of seropositive animals in some areas and herds most probably is the result of animal origin and management on the farms, i.e. movement of animals with introduction of new animals into a herd, what also means that the virus enters into a herd and outbreaks of BVDV infection occur. The titre ofVNantibodies in a certain number of animals, especially on certain areas and in some herds ranged up to 1:512 and even more, what was a clear indication of current or recent presence of persistently infected animals in these herds. High percentage of seropositive animals (70%) in 9 large herds most probably is the result of uncontrolled animal movement, entering of BVD virus and frequent outbreaks of BVDV infections in these herds, but this also indicates probable presence of persistently infected animals in the herds. The obtained results point on high prevalence of BVD infection in the examined area. This prevalence is not equal, what point on existence of areas where the infection is not present, or is present only sporadically.
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