Immune response of fasted calves to infectious bovine rhinotracheitis virus.

Abstract

Seventeen calves (Angus, Hereford, and Angus-Hereford crosses) weighing 120-200 kg, were starved for 3 days and inoculated intranasally with a strain of IBR virus after 1 day or 3 days of food deprivation. Although clinical signs of disease were mild in all calves, the signs appeared more severe than those reported by others using the same strain of virus possibly due in part to the use of intranasal inoculation by aerosol vs instillation. Neutralizing antibody response after virus inoculation did not differ beween groups. Of the 17 calves, 16 developed significant increases (seroconversion of 4-fold increase in titre) in IBR serum antibodies. Serum neutralizing antibodies in 3 calves at inoculation did not prevent them from excreting substantial amounts of virus for ? 5 days after virus inoculation. Lymphocytes from fasted and nonfasted calves had similar (essentially negative) blast transformation responses, except 1 fasted seropositive calf (sensitised animal) that had a high stimulation index. Some dehydration was observed in fasted calves, indicated by significant increase in haematocrit. In only 1 group did serum cortisol levels rise significantly, mean values peaking at the end of fasting at the time of inoculation; thereafter, mean values tended to decline. Although the 3-day fast significantly affected some serum and blood components, it did not adversely affect the immune response of calves. One fasted calf developed a significant cell mediated immune response to inactivated IBR virus during infection. It is concluded that acute nutritional deprivation may not necessarily increase the susceptibility of calves to viral infections nor adversely affect their immune response after vaccination.

This report represents a portion of a dissertation submitted by the senior author to the graduate faculty of the University of Missouri in partial fulfillment of the requirements for the PhD degree.

The authors thank Gary Krause and Mark Ellersieck for aid in statistical analysis and Gerald Buening for help in lymphocyte transformation tests.