Pneumonia is the single greatest cause of deaths in sheep. Nursing lambs (0.5 – 2 months of age) and lambs 5-7 months of age have a higher incidence than animals in other age groups.
The complex cause of ovine pneumonia results from an interaction of Chlamydia, Mycoplasma, bacteria, viruses and stresses. Economic losses result from deaths, reduced live weight, delayed marketing, cost of treatment and ill-thriftiness among survivors.
A sheep producer in the Bathurst area lost 6-8 October drop lambs out of a mob of 180 the week before Christmas 2010. The lambs were not weaned but had been marked, vaccinated (5-in-1, Gudair, Scabby mouth) and drenched (Abamectin) 3 weeks previously. All the lambs that had died were from the same paddock and were the first mob to be marked. All lambs had shown respiratory distress prior to death.
The sheep producer presented a lamb that had died overnight for post-mortem examination.
The lamb had a large amount of cork screw grass seed within the wool. There were 4-5 3cm or greater round lumps that could be felt along the ventral jaw and neckline as well as 10-15 3cm or smaller round lumps in the same area. When incised, thick yellow purulent material was released (See Figure 1).
Opening the chest cavity revealed 100mls of yellow, cloudy fluid with a pungent odour (See Figure 2).
There was a diffuse covering of thick yellow material over the lungs with adhesions obvious between the pleura and lungs (See Figure 3).
Over 80% of the lungs were affected with the cranio-ventral lobes most severely affected. The affected parts of the lungs looked more like the liver than lungs (See Figure 4).
Samples of the lungs were submitted for culture and histopathology.
Histopathology reported multifocal to coalescing, moderate to marked, fibrino-suppurative bronchopleuro-pneumonia with intralesional bacteria.
Bacteriology reported profuse predominant growth of Arcanobacterium pyogenes.
Arcanobacterium pyogenes is a normal inhabitant of the mucous membranes of domestic animals, such as cattle, sheep, swine, and goats. It is also an opportunistic pathogen in these animals, where it causes a variety of purulent infections involving the skin, joints, and visceral organs.