By Forbes District Veterinarian Nik Cronin
I recently investigated a case of sudden death in a mob of local lambs. While the losses had been sporadic over the previous couple of weeks, this particular morning two were found to have died overnight. Post mortem examination confirmed that both had died of a very significant pneumonia. A large percentage of the remaining mob seemed to also be affected with widespread coughing, and a number appearing slightly depressed with increased respiratory rates.
Pneumonia represents a significant cost to the sheep industry, with production losses related to depressed growth rates on farm, deaths and trimming of the carcase at the abattoir.
While pneumonia can be seen at any time of the year and in any class of sheep, we most commonly see it in young sheep in outbreaks like this during summer, hence it is often given the term ‘summer pneumonia’. The disease is most likely set off by an initial viral and/or bacterial infection which can rapidly circulate through the mob. Opportune secondary bacterial invasion of the compromised lung tissue may then lead to more severe clinical disease and larger outbreaks.
Stress leading to increased susceptibility is a significant factor in the development of an outbreak of respiratory disease, and can be precipitated by changes in diet, transport, mixing, crowding and extreme climatic conditions, including temperature and humidity. Breed may also be a factor, with outbreaks more common in cross breds and British breeds. During the drought we also saw pneumonia associated with subclinical acidosis, dusty feed substances, and dry, dusty environments in lot feeding set-ups.
In the recent case I saw, as such a large percentage of the mob was affected we elected to blanket treat with antibiotics and the producers reported a good response. Interestingly enough, over the next week, they noticed several of their other lamb mobs become affected too, also requiring treatment. However, the need for antibiotic treatment must be carefully considered from case to case and take into account withholding periods.