Pasteurella haemolytica biotype A, serotype 1 (P haemolytica A1) was the most commonly isolated Pasteurella species from 80 calves examined at necropsy from 40 outbreaks of respiratory disease, the majority of which were pathologically confirmed as bovine pneumonic pasteurellosis (transit fever; shipping fever). Similarly, nasopharyngeal swabs from in-contact and apparently healthy calves indicated the widespread presence of P haemolytica A1. Pasteurella multocida and other serotypes of P haemolytica A1 were found including six isolations of P haemolytica T10, a fairly common pathogen in sheep. Approximately two-thirds of the isolates were tested for their antimicrobial sensitivity patterns and the degree of sensitivity for P haemolytica A1, the most frequently isolated serotype, was chloramphenicol (100 per cent), sulphamethoxazole trimethoprim (98 per cent), oxytetracycline (80 per cent), ampicillin (85 per cent), penicillin (82 per cent), streptomycin (3 per cent) and lincomycin (1 per cent).

Fifteen incidents of infectious bovine rhinotracheitis (IBR) were studied in herds distributed widely throughout northern Britain. Fattening beef animals (10 outbreaks), dairy cattle (four outbreaks) and suckler beef cows (one outbreak) were affected and all bar one incident occurred in housed cattle during the winter. The first signs of illness noticed were a reduced appetite, dullness, coughing and oculonasal discharge. In 13 of the incidents they were observed in cattle purchased from a market within the previous four weeks. In every outbreak, affected animals developed a serous nasal discharge which became purulent in severe cases. In the early stages the nasal mucosa was congested but later yellow-brown diphtheritic plaques developed. In such animals halitosis was always detected. Soft coughing was frequently heard but pneumonia was rarely confirmed ante mortem. Conjunctivitis and ocular discharge were a major finding in 13 incidents and, in severely affected cases, conjunctival oedema was seen. The drooling of saliva was noticed in 14 incidents but congestion of the oral mucous membranes was the only abnormality found on examination of the oral cavity. Diarrhoea was a consistent feature in one outbreak. As a result of contracting this disease beef cattle failed to put on weight for a period of one to eight weeks and the milk yield of lactating dairy cattle decreased markedly. The morbidity rate was high, being more than 90 per cent in 10 incidents. The mortality rate varied considerably but 7 to 8 per cent of the animals died, or were culled, in three outbreaks. The clinical signs were most severe on intensive units with a high turnover of cattle.

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A strain of Pasteurella haemolytica biotype A serotype 1, which had been isolated from a pathologically-confirmed outbreak of bovine pneumonic pasteurellosis, was used successfully to reproduce the disease in conventional calves. The development of the various pathological features was studied at regular intervals following infection. The acute inflammatory reaction which had developed by day 2 after initial infection was characterised by flooding of the alveoli by oedema and neutrophils together with a mild degree of bronchiolar epithelial necrosis. This progressed to an acute exudative fibrinous pneumonia with extensive involvement of the interlobular septa and often with pleurisy. Subsequently, these pulmonary lesions became walled off by fibrous tissue which became infiltrated by plasma cells and lymphocytes. At this stage organisms could be demonstrated only within these nodules in the lung tissue.

An acute pneumonia was induced experimentally in 10, 10- to 12-week-old conventional calves by administration into the upper airways of a pathogenic strain of parainfluenza type 3 (PI3) virus. The experimental calves had been selected on the basis of freedom from clinical evidence of respiratory and other diseases, freedom from current infection by PI3 virus as judged by repeated nasopharyngeal swabbing and freedom from earlier PI3 virus infection as judged by their lack of significant levels of serum antibody to that virus. The infection procedure was deemed to have been successful in that infection was established with subsequent seroconversion, clinical signs of a febrile pneumonia arose soon after the administration of virus, histopathological changes characteristic of PI3 pneumonia developed and the presence of PI3 virus antigen was demonstrated by immunofluorescence in association with those lesions. Treatment of five of the pneumonic calves was carried out on days 1, 2 and 3 of the trial using the anti-prostaglandin compound flunixin meglumine and that treatment appeared to be of benefit in that in the test calves there was a prompt cessation of coughing with fewer fevers and lower respiratory rates as compared with the untreated controls. The drug did not appear to influence PI3 infection rates but its administration was associated with a marked reduction in the extent of pulmonary consolidation, probably as the result of its known ability to limit the acute inflammatory response.