Time to detect BVD in bulk tank milk

Does bulk tank milk antibody testing provide timely information about BVDV introduction into herds?

The summarised findings of this article: Stochastic simulation modelling to determine time to detect Bovine Viral Diarrhea antibodies in bulk tank milk, by Foddai et al. (Preventive Veterinary Medicine (2014)) should be considered when evaluating the usefulness of bulk tank milk antibody screening.

Surveillance is often based on initial bulk tank milk (BTM) antibody ELISA screening however test performance may not be constant over time or in herds of differing numbers e.g. the prevalence of antibody positive milking cows in the herd will influence detection.

Study objectives

• Determine whether herd size or ELISA test used would significantly affect the detection time after BVDV introduction
• Compare detection times of three antibody ELISAs (Danish blocking ELISA, Svanovir BVDV-Ab ELISA, indirect ELISA Pourquier (BVD/MD p80 milk ELISA test))

Materials and Methods

Development of a model to simulate BVDV spread throughout a herd. Valid assumptions were made based on recent, relevant literature and with reference to Danish dairy herd management N.B. vaccination is not permitted in Denmark.

Results 

Smaller herds have faster BTM antibody detection following BVDV introduction, however the route of BVD introduction (PI or TI) plays a significant role. Svanovir BVDV-Ab ELISA showed the shortest detection time; detected antibodies in the BTM of a large herd 280 days after introduction of a TI milking cow. The estimated time to detection after introduction of a PI calf was 111 days.

Conclusion

The findings of this study are important because the risk of spreading BVDV to other herds through trading PIs and TIs is positively correlated with time to detection. Faster detection would also lower the disease impact i.e. reduce the incidence of PIs and dead calves, resulting in improved welfare and farm income.