Experimental exposure of feedlot cattle to infectious bovine rhinotracheitis virus

Abstract

An axiom of infectious disease research states that significant numbers of animals with typical clinical disease must be observed to provide data for analysis. The morbidity rate of naturally occurring bovine respiratory disease (BRD) in feedlot cattle is frequently great enough to provide adequate data. In 2 successive years, the low incidence of respiratory disease in feedlot cattle at the Veterinary Medical Research Farm precluded analysis of the data. An alternative to the chance occurrence of spontaneous disease was experimental induction of BRD. Of the etiological trial of BRD, stress, virus and bacteria, a virus component appeared to provide the most potential for a controllable system. Exposure of cattle to pasteurella has given unpredictable results. A BRD inducing level of stress would be very difficut to simulate in large numbers of cattle. Aerosol exposure of calves to bovine herpesvirus-1 and 4 days later to Pasteurella hemolytica has been reported to consistently produce fibrinous pneumonia. The relationship of this experimentally induced disease to “shipping fever” is not clearly understood.1 Although this model is useful for experiments designed with small numbers of calves, it did not fit the needs for a larger scale controlled clinical trial. Therefore, we elected to expose newly arrived cattle to infectious bovine rhinotracheitis virus (IBRV) in an attempt to initiate BRD. This report presents the results of trials, conducted on each of 4 consecutive years.