Bacteria associated with calf pneumonia and their effect on gnotobiotic calves.

Samples of pneumonic lung tissue from 140 calves with subclinical pneumonia and 65 calves with fatal pneumonia were examined bacteriologically. Sixty-eight (48 per cent) of the lungs from the subclinical cases and 27 (41 per cent) of the lungs from the fatal cases contained bacteria at more than 10(4) colony forming units (cfu) per gram of tissue. Pasteurella haemolytica was associated more with fatal cases than subclinical cases (P less than 0.001). Of the seven species of bacteria inoculated endobronchially into gnotobiotic calves only P haemolytica produced severe respiratory disease, although some strains of P multocida produced a fatal septicaemia.