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 (r2 = 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.