Evaluation of Type II Killed BVD Vaccine in the Face of Type II BVD Challenge

Type II BVD continues to be a concern for cattle producers. Type I MLV BVD vaccines reportedly provide adequate protection against disease caused by Type II BVD. However, MLV vaccines cannot be used in all management situations. This study was designed to test the efficacy of an experimental killed Type II BVD vaccine. In addition, the study compared results with efficacy of modified live and killed Type I BVD vaccines, as well as with efficacy of a killed Type II/MLV Type I combination.

Type II BVD continues to be a concern for cattle producers. Type I MLV BVD vaccines reportedly provide adequate protection against disease caused by Type II BVD. However, MLV vaccines cannot be used in all management situations. This study was designed to test the efficacy of an experimental killed Type II BVD vaccine. In addition, the study compared results with efficacy of modified live and killed Type I BVD vaccines, as well as with efficacy of a killed Type 11/MLV Type I combination.
Cattle (n=30) that were seronegative against BVD (SN<l:2) were divided into five test groups of six animals each. On days O and 14, cattle were bled and vaccinated with one of the following preparations: 1) MLV Type I BVD vaccine. This vaccine was prepared according to the current outline of production for MLV BVD vaccine. Product was reconstituted and administered according to the label directions at the time of use. 2) Killed Type I BVD vaccine. This vaccine was prepared according to the current outline of production for KBVD vaccine. Product was administered according to the label directions. 3) Killed Type II BVD vaccine. This · vaccine was prepared and formulated according to the current outline of production for KBVD vaccine except that Type II BVD Strain 125 (NVSL, Ames, Iowa) was used in place of strain C24V. 9CFR final product release tests were performed on the final product. Animals were inoculated with 2 ml of the preparation contain-156 ing no less than 6.5 logs of Type II Killed BVD virus per dose. 4) Killed Type I BVD/MLV Type II BVD vaccine. MLV Type I BVD vaccine was reconstituted with the killed type II BVD vaccine described in 3). 5) RPMI 1640 (untreated control). Calves were bled on days 21 and on day of challenge. Calves from each group were challenged with Type II BVD (BVD CHV, "890" 94-9, 11/94, NVSL, Ames, Iowa) according to the NVSL Type II challenge protocol on day 28. After challenge, animals were observed daily. Daily rectal temperatures were obtained and clinical signs were scored according to the Diamond Animal Health Carlisle Research Facility scoring key. Daily nasal swabs were taken for virus isolation. Additional serum samples were collected 7 and 14 days after challenge. All serum samples were assayed for the presence of both Type I and Type II BVD-neutralizing antibodies.
Data from clinical scores, viral shedding and serum neutralization studies were statistically evaluated to determine the relative efficacies of the different vaccines. Results showed that the killed Type II, the MLV Type I, and the killed Type 11/MLV Type I combination vaccines were effective in protecting calves from Type II BVD challenge, while the killed Type I vaccine was not. Serum neutralization titers suggested that the killed Type II vaccine might confer longer duration of immunity than the MLV Type I vaccine.
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