Abattoir surveillance in NSW has shown that pleurisy and pneumonia is a significant problem for the Australian sheep industry with 2% of carcases per annum showing evidence of the disease. Respiratory disease with terminal Pasteurella or Mannheimia pneumonia is the main cause of death in feedlot cattle especially in North America. The aetiology and epidemiology of respiratory disease in cattle has been extensively studied. In Australia 'summer pneumonia' in young sheep has been described. In my experience pneumonia has been a sporadic problem in weaner sheep. This report describes an outbreak of Mannhiemia pneumonia in 2-4 week old lambs which I believe to be unusual.
The owner from between Bathurst and Orange runs a self-replacing Merino flock of 450 Merino ewes on improved pastures . The flock lambs in mid-July to the end of August and usually marks about 370 lambs. For several years up to six of the most well grown lambs 2-4 weeks of age have died suddenly before marking. Deaths have mostly occurred in the one paddock. This year the owner reported the sudden death of 15 well-grown 2-4 week old lambs.
A single well grown lamb of about 3 weeks of age was presented for post-mortem on 3 August 2006 and three lambs were examined on 22 August 2006. The first lamb had fibrinous pleuropneumonia in the apical lobes of both lungs. Of the three lambs subsequently examined one had a marked bronchopneumonia involving virtually all of the right lung and the apical lobe of the left. Mannheimia haemolytica was isolated from both cases that presented with pleuritis and bronchopneumonia. The cause of death was not apparent in the other two lambs.
Not all the lamb deaths were likely to have been caused by pneumonia. As the lambs had not yet been marked or vaccinated clostridial diseases for example could have been responsible for some. Nonetheless, two of four deaths in the lambs examined were due to fibrinous pleuropneumonia which I believe to be most unusual in lambs of this age.