Pulmonary botryomycosis in a Scottish highland steer.

Pertinent necropsy findings in a 5 1/2-year-old Scottish Highland steer with chronic intractable pneumonia and cough were limited to the pulmonary system. The accessory lobe of the lung was collapsed, scarred, and multifocally adhered to parietal pleura. A polypoid mass almost completely obstructed the lobar bronchus and protruded into the trachea; mucopurulent exudate distended more distal bronchi. Botryomycosis was diagnosed when histologic examination revealed pyogranulomatous pneumonia with eosinophilic granules and "club" formation surrounding colonies of gram-positive cocci. Staphylococcus aureus was cultured from the lung. Botryomycosis is an unusual response to infection with common bacteria and is characterized by pyogranulomatous inflammation with formation of eosinophilic granules surrounding colonies of gram-positive cocci or gram-negative bacilli. Among domestic species, staphylococcal botryomycosis is most common as a wound infection in horses or as mastitis in cows and sows. Pulmonary botryomycosis is rare in horses, humans, and guinea pigs and apparently has not been reported in cattle.