Monitoring of BVDV by testing antibodies to NS3 protein in calves vaccinated with an inactivated BVDV vaccine.

H. Kuijk¹,^* G. Nijhoving¹ Linda van Duijn² M. Mars² W. Theuws³ H. Swam¹ B. Makoschey¹

¹MSD Animal Health, Boxmeer, ²GD Animal Health, Deventer, ³DAC De Peelhorst, Uden, Netherlands

Objectives: 

On many BVDV free certified farms in the Netherlands, cattle are vaccinated with the inactivated vaccine Bovilis BVD (MSD Animal Health) to reduce the risk that new PIs are born. The BVDV free status of a farm can be monitored by 6-monthly spot blood testing of 5 calves in the age of 8 to 12 months for the presence of NS3-antibodies. Sometimes calves have been vaccinated before they have been tested. The aim of this study was to determine whether vaccination with Bovilis BVD might interfere with this monitoring system in calves.

Materials and Methods:

In 8 BVDV free certified herds, 5 calves in the age group 8-12 months were vaccinated with Bovilis BVD according to manufactures instructions and 5 sentinel calves were left unvaccinated.

Blood samples were taken from all calves on day 1 (first vaccination), day 28 (second vaccination), day 56, day 112 and day 168 and tested for NS3 antibodies in the Prionics BVDV ELISA.

Blood samples taken on day 56, day 112 and day 168 were also tested for Virusneutralising antibodies (VNT). In one herd, blood samples from all calves between 1 and 16 months of age were tested for BVD virus.

Results: 

All vaccinated calves showed high VN titers on days 56, 112 and 168. In 5 herds (A,B,C,D,E) neither vaccinated nor unvaccinated calves developed ns3 specific antibodies as measured by ELISA. In the herds F, G, H, all unvaccinated calves tested negative for antibodies as measured by ELISA.In 1 herd (F) 1 vaccinated calf showed a low titer in ELISA on day 56, but was tested negative at day 112.In 1 herd (G) 2 vaccinated calves showed low titers in ELISA on day 56, these titers were undetectable on day 112. In 1 herd (H) all 5 vaccinated calves showed moderate titers on day 56, these titers declined to very low titers on days 112 and 168. Because of the moderate titers on day 56, in this herd, blood samples from all calves between 1 and 16 months of age were tested for BVD virus. No PI animal was found.

In 6 out of the 8 herds included in this study vaccination of the calves did not at all interfere with the young stock monitoring using NS3- ELISA. In 1 herd, it was required to test an additional 5 calves by antibody ELISA to confirm the BVDV-free status. It remains unclear whether the relative high titers in the 8th herd were caused by i) the vaccination, ii) by transient BVDV infection, or iii) by infection from a PI that was already removed from the herd at the time of testing.

Conclusions: 

Young stock monitoring can be applied in herds vaccinated with the inactivated BVDV vaccine used in this study. All vaccinated calves developed high neutralizing antibody titers. Only a small proportion of vaccinated animals developed low, short lasting titers of BVDV-NS3 specific antibodies as measured by NS3-ELISA, potentially hampering young stock monitoring. It is therefore recommended to either take blood samples before vaccinating or to monitor on vaccinating farms by antigen detection methods.