Evolution of the Seroprevalence of Pestivirus and Respiratory Viral Infections in Spanish Feedlot Lambs

SIMPLE SUMMARY: The presence of viruses, such as bovine parainfluenza type 3, bovine herpesvirus type 1, bovine respiratory syncytial virus and pestiviruses, has been widely demonstrated in sheep in the past, but it is unknown how these infections may affect the lambs during their fattening period under commercial conditions. In the present study, the exposure to the aforementioned viruses was studied in 120 feedlot lambs throughout the whole fattening period. Seroprevalences were measured by enzyme-linked immunosorbent assays (ELISA), relating their presence to health and production parameters in the studied lambs. During the studied period, the lambs seroconverted against 3 out of the 4 viruses analysed and only 10.8% of the lambs were seronegative for all the tested viruses throughout the entire study. Finally, no associations were found between the seroconversion to one or more viruses and the presence of respiratory clinical signs or lung lesions at the slaughterhouse. In addition, no disturbances were observed in the performance of the lambs, except in the case of pestivirus infections, for which the presence of antibodies in the animals was associated with reduced final weight at the end of the fattening period. ABSTRACT: The presence of respiratory viruses and pestiviruses in sheep has been widely demonstrated, and their ability to cause injury and predispose to respiratory processes have been proven experimentally. A longitudinal observational study was performed to determine the seroprevalence of bovine parainfluenza virus type 3 (BPIV-3), bovine respiratory syncytial virus (BRSV), bovine herpesvirus type 1 (BHV-1) and pestiviruses in 120 lambs at the beginning and the end of the fattening period. During this time, the animals were clinically monitored, their growth was recorded, and post-mortem examinations were performed in order to identify the presence of pneumonic lesions in the animals. Seroconversion to all viruses tested except BHV-1 was detected at the end of the period. Initially, BPIV-3 antibodies were the most frequently found, while the most common seroconversion through the analysed period occurred to BRSV. Only 10.8% of the lambs showed no detectable levels of antibodies against any of the tested viruses at the end of the survey. In addition, no statistical differences were found in the presentation of respiratory clinical signs, pneumonic lesions nor in the production performance between lambs that seroconverted and those which did not, except in the case of pestiviruses. The seroconversion to pestiviruses was associated with a reduction in the final weight of the lambs.