Antibody Response to Mannheimia Haemolytica Leukotoxin in Cattle with Respiratory Tract Disease

In order to obtain data concerning the involvement of Mannheimia haemolytica in bovine respiratory disease (BRD) outbreaks, a serological survey was carried out on paired (acute- convalescent) sera from 1310 beef and 810 dairy cattle collected in 262 BRD outbreaks in Italian herds during 2002-2006. No vaccination program to M. haemolytica A1 was applied in the investigated herds. For each outbreak, 5 to 12 animals were considered for serum sampling. An enzyme linked immunosorbent assay (ELISA) was used to determine serum antibody response to M. haemolytica leukotoxin (LKT). Seroconversion involved 467 animals (22%), 314 beef cattle (24%) and 153 dairy cattle (19%), respectively. On a serological basis, M. haemolytica involvement was detected in 162 (62%) BRD outbreaks. Prevalence of seroconversion ranged from 20% to 60%. Concurrent seroconversion to M. haemolytica and the main bovine respiratory viruses was re- corded in 141 (54%) outbreaks. Seroconversion to M. haemolytica LKT involved mainly cattle not vaccinated to BRD vi- ral agents.