PERFORMANCE, SURVIVAL, NECROPSY, AND VIROLOGICAL FINDINGS FROM CALVESPERSISTENTLY INFECTED WITH THE BOVINE VIRAL DIARRHEA VIRUS ORIGINATING FROM A SINGLE SASKATCHEWAN BEEF HERD

Fifty-one calves from 652 cows and heifers that calved on a Saskatchew an ranch in 1992 were identified as persistently infected with bovine viral diarrhea virus (BVDV), based on virological and necropsy finding s. Herd records suggested a further 20 calves that died between birth and weaning were probably also persistently infected. Subsequent to we aning, all surviving persistently infected calves were transferred to one pen in a 10 000 head commercial feedlot, to mimic normal managemen t practice in western Canadian beef herds. On average, when compared w ith healthy, BVDV-negative herdmates, persistently infected calves wer e ''poor doers'' and had poor survivability, with only 4 persistently infected calves surviving to 1 year of age. There was no difference (P > 0.05) in survival between male and female persistently infected cal ves. The clinical, pathological, and virological findings from these p ersistently infected calves varied over time. The majority of persiste ntly infected calves had gross pathological lesions at necropsy, consi stent with mucosal disease. However, approximately 25% of the persiste ntly infected calves had gross pneumonic lesions at necropsy, with no or only mild lesions of mucosal disease. A wide variety of other lesio ns were also noted in persistently infected calves at necropsy. Theref ore, the possibility that BVDV-induced lesions can be misdiagnosed is very real. The results of this study indicate that persistent infectio n with BVDV should always be considered in calves with chronic ill thr ift, chronic enteritis, or respiratory disease.