Milk as a diagnostic sample for a commercially available ELISA to identify bovine viral diarrhoea (BVD) antibodies in dairy herds

Abstract

OBJECTIVE: The aims of this study were to evaluate a commercially available ELISA for the detection of bovine viral diarrhoea virus (BVDV)-specific antibodies in individual milk compared with individual serum samples, and in bulk milk samples compared with within-herd antibody prevalence and bulk milk quantitative reverse transcription polymerase chain reaction (qRT-PCR) results. METHODS: Paired individual serum and individual milk samples were collected from 125 lactating cows and tested by ELISA; 96 bulk milk samples were also tested. Within-herd antibody prevalence was calculated based on milk ELISA results for 25 individual cows in each herd. Additionally, 167 bulk milk samples were tested for BVDV-specific antibodies by ELISA and for the presence of BVDV by qRT-PCR to establish the correlation between antibody result and virus presence. RESULTS: Good agreement was observed between individual milk and serum results (Kappa = 0.865). The ELISA was observed to detect BVDV-specific antibodies in individual milk samples with a relative sensitivity of 96.6% and specificity of 89.2%. The bulk milk samples revealed a strong (r(2) = 0.95) relationship between the ELISA result and the within-herd antibody prevalence. The proportion of herds that tested positive by bulk milk qRT-PCR increased as the bulk milk antibody S/P ratio increased. CONCLUSION: Commercially available ELISA testing of individual and bulk milk samples is an appropriate alternative to serum testing with good test performance in these samples. Determining a threshold for the detection of herds containing active BVD infection by testing bulk milk is a novel use for an antibody ELISA kit and provides more practical, relevant test results.