The prevalence of bovine viral diarrhea virus (BVDV) infection was examined in a population of 5129 recently weaned steer calves entering a large feedlot in central Saskatchewan from September to December 1991. Serum samples were collected within 24 h of arrival at the feedlot from every fifth calf processed and again 96 d postarrival. A microtiter virus isolation test was used to determine the prevalence of calves viremic with BVDV on entry to the feedlot. An enzyme-linked immunosorbent assay (ELISA) which detects antibody against glycoprotein 53 of the BVDV was used on paired sera to determine the seroconversion risk during the first 96 d in the feedlot. A virus neutralization (VN) test for BVDV was conducted on a sub-sample of paired sera to measure agreement in determination of seroconversion risk with the ELISA. A polymerase chain reaction (PCR) test which detects BVDV was used to determine if cattle were acutely viremic when treated for disease. The estimated prevalence of persistently infected calves in this population was < 0.1%. The seroconversion risk for BVDV was 27% (236/864) according to the ELISA and it varied from 0 to 63% among the 20 pens sampled. According to the VN test, the seroconversion risk for BVDV was 40% (132/327) and it varied from 0 to 100% among the 11 pens tested. The agreement between the ELISA and VN tests in seroconversion risk to BVDV was very poor (kappa = 0.15 +/- 0.039 SE). The prevalence of acute viremia in calves treated at the feedlot hospital was low at 4% (6/149). Although the prevalence of persistent infection was low, serological tests suggested a high risk of seroconversion to BVDV. Unfortunately, the detailed epidemiology of acute BVDV infection in this feedlot could not be described because of the lack of agreement between the two serological tests. The two tests classified different individuals and groups of calves as having been infected with BVDV during the first 96 d in the feedlot. While the benefits of the ELISA for BVDV may seem considerable, the dynamics of the titer change and their interpretation subsequent to natural exposure to BVDV, need to be better defined before these tests can be used with confidence in future feedlot studies.
Taylor LF, Van Donkersgoed J, Dubovi EJ, Harland RJ, van den Hurk JV, Ribble CS, and Janzen ED. Can J Vet Res. 1995 April; 59(2): 87–93.