Calves purchased from auction markets from several states were delivered to the Oklahoma State University Sparks facility and held for approximately 60 days. There were three separate studies in 2009 (148 calves, 164 calves and 363 calves) representing mixed-source, post-weaned beef breed calves.
The calves were processed including a modified-live (MLV) viral vaccine shortly after arrival and repeated two weeks later. Calves, including 20–22 sentinels and all sick calves in each study, were sampled with acute and convalescent serums for serology. Nasal and lung lavage samples were collected from the sentinels on weekly basis for viral isolation. All sick cattle in the initial 14 days were also sampled for nasal swabs and lung lavages when initially treated and at day 56.
Bovine coronavirus (BCV) was recovered from day 0 collections in a high number of the sentinel calves in the three studies (40.9%, 75% and 85%), primarily in the nasal swabs but many from the lung lavage. In two studies with available weekly samples, the calves cleared the infections by day 8. Interestingly, calves BCV-positive had no or low antibody levels to BCV at day 0. Selected sick calves also had BCV in the nasal swabs and lung samples. Calves under these feedlot conditions uniformly seroconverted to BCV (75% to 95%).
No other viruses were identified in these calves; however there were isolates of bovine herpesvirus-1 (BHV-1) and bovine viral diarrhea virus (BVDV) recovered in two studies from nasal swabs and lung lavage samples post-vaccination, usually in the day 8 collection. In one study the BHV-1 shared genetic identity to the vaccine virus in the MLV, and in another study the BVDV isolates were identical to the MLV BVDV vaccine strain. The calves cleared the BHV-1 and BVDV by day 14.
These findings indicate that BCV can be found in clinically ill cattle with BRD, and also in healthy cattle. They clear the BCV within days of arrival. Also finding BHV-1 and BVDV in calves postvaccination may indicate vaccine strains, which are expected to be cleared. However, the BVDV isolated early after processing needs to be differentiated from naturally occurring field strains.
This case study was provided by Robert Fulton, DVM, PhD, Oklahoma State University.