Embolic pneumonia is the result of showering of septic thrombi into the pulmonary arterial system from major veins such as the caudal vena cava, mammary, uterine and jugular veins. Septic thrombi result from bacterial infections in tissues resulting in erosion into veins and releasing thrombi into the circulatory system. Erosion into the caudal vena cava of hilar liver abscesses is a well known sequel to ruminal acidosis. Animals surviving the thromboembolic showering event may later develop pulmonary arterial aneurysms which may rupture into a bronchus causing rapid blood loss and death.
Animals are usually found dead from massive embolism of the lung or rupture of a septic embolus into a bronchus and rapid blood loss.
In some cases affected animals are noticed antemortem with sudden development of a cough, respiratory distress and bleeding from the nose and mouth. A period of ill thrift followed by these signs may indicate that sudden death is imminent.
At necropsy there is severe widespread discolouration, abscessation and haemorrhage affecting the lungs. Further dissection may find an abscess at the hilus of the liver that has eroded into the vena cava, or where infection of other organs and tissues has entered other large veins.
There is no treatment. Cattle showing sudden deterioration in strength and demeanour that are in respiratory distress should be euthanased without delay.
Preventing ruminal acidosis will reduce formation of liver abscesses, the most common cause of embolic pneumonia.