IN-VIVO PRODUCTION OF NEURAMINIDASE BY PASTEURELLA-HAEMOLYTICA IN MARKET STRESSED CATTLE AFTER NATURAL INFECTION

Pasteurella haemolytica (Ph) is the most important cause of the bovine acute fibrinohemorrhagic pneumonia that occurs in market stressed cal ves after shipment to feedyards. Recent characterization of neuraminid ase production by these organisms has shown that all 16 serotypes prod uce an immunologically similar form of the enzyme. Anti-neuraminidase antibody against PhA1 and PhA6 was determined in 101 2- to 5-month-old calves, on their farms of origin, at the order buyer barn (OBB), and through 28 days in the feedyard. Half of the calves were vaccinated wi th a killed Ph serotype-A1 (PhA1) product. Nasal secretion and tonsil wash specimens were cultured for Ph and Pasteurella multocida (Pm). Se rum antibody against PhA1 and PhA6 was measured by indirect hemaggluti nation (IHA), and anti-neuraminidase antibody was determined by the ne utralization assay. At the feedyard, 73 calves had respiratory tract d isease. IHA values ranged between 1:2 and 1:1024 for PhA1 and between 1,2 and 1:512 for Ph serotype A6 (PhA6). Forty-two, 24, and 28% of the calves were infected with PhA1, PhA6, and Pm, respectively. Ninety-si x percent of the calves experienced an increase in anti-PhA1 neuramini dase antibody when sera drawn on feedyard day 28 were compared with se ra drawn on the farm. These data demonstrate that the enzyme neuramini dase is produced in vivo in market stressed cattle after a natural Ph infection.