Clinical and epidemiological features of 15 incidents of severe infectious bovine rhinotracheitis.

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.