THE ROLE OF PASSIVE-IMMUNITY IN BOVINE RESPIRATORY SYNCYTIAL VIRUS-INFECTED CALVES

The role of passive immunity in bovine respiratory syncytial virus (BRSV) infections in neonatal calves was evaluated. Calves were divided into groups as follows: colostrum-deprived, sham-inoculated; colostrum-deprived, BRSV-inoculated; and colostrum-fed, BRSV-inoculated. Calves were inoculated with a low-passage field isolate of BRSV for 4 consecutive days by a combined respiratory tract route and were euthanized 6 days after receiving the last inoculation. Arterial oxygen tension (Pao2) decreased significantly over time in colostrum-deprived, BRSV-inoculated calves (P < .01) and was significantly different among treatment groups (P < .05). A significant decrease in arterial oxygen saturation was observed in this same group over time (P < .01). Mean percentage of pneumonic lung volume (determined by computer data digitalization) was significantly greater in infected, colostrum-deprived calves compared with the other groups (P < .01), and BRSV antigen was detected in these calves by avidin-biotin immunoperoxidase staining. Thus, passive immunity derived from colostrum feeding decreased the severity of BRSV infections in calves.