Multiplex PCR assays detect M. haemolytica in B. trehalosi/M. haemolytica cocultures, when colony PCR and bacteriological assays are negative. Lane 1, B. trehalosi monoculture (144 bp); lane 2, M. haemolytica monoculture (267 bp); lanes 3 to 7, B. trehalosi and M. haemolytica in cocultures collected after 0, 6, 12, 24, and 30 h of culture, respectively; lane 8, molecular weight markers. The results of one representative experiment out of three are shown.