The prevalence of bovine viral diarrhoea antibodies in selected South African dairy herds, and control of the disease

The prevalence of bovine viral diarrhoea (BVD) serologically positive anima ls in 18 dairy herds with clinical and pathological lesions suggestive of B UD infection, the post-vaccinal seroconversion rates in negative animals va ccinated twice with an inactivated BVD vaccine, and the control measures ta ken, are described. The pathological and histopathological findings in 6 ne cropsies performed on animals that died in 5 separate herds closely resembl ed published descriptions. Positive immunohistochemistry results in 3 cases confirmed the diagnosis in those animals. In 1 herd the prevalence of prev accinal BVD antibodies was only 36.8 %, while the prevalence varied from 79 .85 to 100 % in the remainder. Control measures taken included immunoprophy laxis with an inactivated vaccine, culling animals that were serologically negative after vaccination that were regarded as probably persistently infe cted (PI) and the implementation of additional biosecurity measures, nle pr evalence of serologically negative PI animals in 10 herds varied from 0.38 to 4.04 %, with 8 herds less than 1 % and 2 herds at 2.79 ro and 4.04 %, re spectively. Methods based on vaccinating the herd, followed by serological testing and culling cattle that did not develop an antibody titre, are not reliable. The identification of PT animals should be confirmed by isolation of the virus or identification of the antigen.