ASSOCIATIONS BETWEEN VIRAL-INFECTIONS AND RESPIRATORY-DISEASE IN ARTIFICIALLY REARED CALVES

Market-purchased, week-old, dairy bred calves entering a commercial ca lf-rearing unit were blood sampled at six-week intervals until three m onths old. Viral infections were monitored by ELISA for antibodies to bovine herpesvirus 1, bovine respiratory syncytial virus, parainfluenz avirus-3, bovine adenovirus subgroup 1 and bovine viral diarrhoea viru s (BVDV). The immunoperoxidase test was used to detect BVDV in serum. The total immunoglobulin concentration in the initial blood sample was measured by the zinc sulphate turbidity test. The relationship betwee n clinical respiratory disease, viral seroconversion and the initial c oncentration of serum immunoglobulin was investigated by the use of th e relative risk statistic, Fisher's exact test, chi2 techniques and th e correlation coefficient. Treatment rates for respiratory disease of 45 per cent were observed during the first period of the study and 19 per cent during the second period. During the first period there was a significant positive association between clinical respiratory disease and seroconversion for all the viruses except parainfluenzavirus-3 an d BVDV but in the second period there was no such relationship. Simila rly, in the first period, but not in the second, there was a significa nt negative association between clinical respiratory disease and both antiviral immunoglobulin as measured by ELISA and total immunoglobulin as measured by the zinc sulphate turbidity test. Two of the 536 calve s that survived to three months of age were found to be persistently i nfected with BVDV.