Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: February 22, 2012
Publication Date: N/A
Technical Abstract: Two trials (T1 and T2) were conducted to examine the range of responses elicited against bovine viral diarrhea virus (BVDV) by vaccination with modified live vaccine and to determine the level of response required for prevention of clinical disease. For T1, BVDV neutralizing (BVDV VN) titers were determined on 216 beef calves (177.03 ± 30.05 kg BW) 20 d after the booster vaccination (49 d from initial vaccination) with a MLV. The presence of titers against BVDV was also measured using a commercial ELISA. Trial 2 utilized 120 beef calves (141.06 ± 29.43 kg BW) that followed the same vaccination protocol in T1, but an extra sample was obtained to determine circulating white blood cell counts (WBC) when blood samples were obtained for determination of antibody response. For T2, titers against BVDV were only determined using the commercial ELISA. In both trials 12 calves were chosen to represent 3 distinct titer groups that consisted of: low (titer < 1/4), mid range (titer 1/4 to 1/16), and high (> 1/16) range response to vaccination (n was 4 calves per group). Calves were moved to BL2 containment and challenged with a high virulence BVDV strain. Basal temperatures were monitored and blood samples were collected on d -2, 2, 4, 6, 9, 11 and 13 post challenge to determine levels of circulating white blood cells, viral shed, and levels of BVDV VN titers. For both T1 and T2 dam age did not differ among the 3 titer groups, but birth weight tended to be largest for the low titer and smallest for the high titer group. Differences in weight gain were also apparent at 49 d post vaccination with the calves in the low group having reduced gains. Titers greater than 1/16 were protective for the calves measured in T1, but calves in the mid and low titer groups had a decrease in circulating WBC and lymphocytes on d 4. Since a correlation between WBC on day -2 and a protective response elicited by vaccination for the 12 calves in T1 was observed, WBC was determined for all calves in T2. A positive correlation was observed between WBC and level of BVDV antibodies as determined by ELISA for calves in T2. Results from these 2 trials provide evidence that there is a relationship between WBC and the response to vaccination. Further investigation prior to vaccination is warranted to discern if vaccination changes WBC or if WBC alters response to vaccination.