Effects of naturally acquired gastrointestinal nematode infection on bovine viral diarrhea virus vaccine-directed antibody response in western Canadian feedlot cattle.

Objective: To determine how gastrointestinal nematode (GIN) infection, reflected by fecal egg counts and serum antibody titers, is associated with the antibody response to bovine viral diarrhea virus type 1 (BVDV-1) vaccine antigen in fall-weaned feedlot cattle from western Canada.

Animals: Cross-sectional study with 240 steer calves derived from an auction market.

Procedure: At feedlot arrival, calves were given a commercial vaccine containing modified live BVDV-1. Serum neutralization antibody titers against BVDV-1 antigens were determined in individual blood samples collected pre-vaccination and 21 d after vaccination. A modified Wisconsin sugar floatation method was used to obtain individual calf GIN egg counts in fecal samples on arrival. Antibody titers against were determined using an enzyme-linked immunosorbent assay in on-arrival blood samples.

Results: Fecal egg counts and titers were not associated with vaccine antibody-fold changes. Similarly, fecal egg counts and titers were not associated with vaccine-induced seroconversion.

Conclusions: The relatively low GIN burdens, reflected by the overall low fecal egg counts in these fall-weaned feedlot calves, did not have measurable adverse effects on the humoral immune response to BVDV-1 vaccine antigens.

Clinical Relevance: An adequate response to vaccination is important for cattle welfare and productivity. Conditions that negatively affect this response may vary regionally, such as GIN infection. Understanding this is essential. Although subclinical intestinal parasitism did not noticeably affect the antibody response in these steers, higher GIN burdens and actual immune protection from clinical disease remain to be investigated.