CONCURRENT BOVINE VIRAL DIARRHEA VIRUS AND SALMONELLA-TYPHIMURIUM DT104 INFECTION IN A GROUP OF PREGNANT DAIRY HEIFERS

Two days after being imported into the United Kingdom one of a group o f 30 pregnant dairy heifers showed clinical signs of bovine viral diar rhoea virus (BVDV) infection and subsequently died, Before it died the heifer was BVDV antigen-positive and antibody-negative. The gross pos t mortem findings were suggestive of mucosal disease but in addition t o noncytopathic BVD virus, Salmonella typhimurium DT104 was cultured f rom tissues and gut contents, The other heifers were screened for S ty phimurium by culturing faeces, and serology showed that 13 (45 per cen t) of the group seroconverted to BVDV in the three weeks between sampl ings and the remainder were seropositive, indicating previous exposure , During this period four heifers showed clinical signs of acute BVDV infection but recovered uneventfully, Four animals (14 per cent) were positive for S typhimurium DT104 on faecal culture, and three of these excretors concurrently seroconverted to BVDV, Of the 29 heifers remai ning in the group, one aborted in late gestation, 26 bore live calves and two delivered stillborn calves, Pre-colostral blood samples from t he calves showed that their darns' pre-existing antibody titres correl ated well with in utero fetal protection, In non-immune darns, exposur e to BVDV between 69 and 120 days of gestation led to the birth of liv e persistently viraemic calves, Infection between 120 and 140 days of gestation led to the birth of live calves with evidence of congenital damage to the central nervous system, and infection later than 140 day s of gestation led to the birth of live, normal calves with high pre-c olostral antibody titres to BVDV, One calf which sucked colostrum was antibody and virus antigen-positive when sampled at 12 hours old but r egular blood sampling failed to detect viraemia again until the calf w as seven weeks old when it became persistently viraemic.