Diagnosis and treatment of respiratory disease in adult sheep based upon ultrasonographic examination of the chest

Introduction - A presumptive aetiological approach is commonly adopted for the treatment of ovine respiratory diseases. This article reports the efficacy of certain treatment strategies for some of the common respiratory diseases based upon ultrasonographic abnormalities affecting the lungs of adult sheep.

Aim - The aim of this study was to report the treatment success of chronic lung diseases in adult sheep where the diagnosis was based upon ultrasonographic examination of the chest.

Materials and methods - Cases were presented to the author in first opinion farm animal practice in the United Kingdom over a two years' period (2010-2011 inclusive). Ultrasonographic examination of the chest was undertaken in nine adult sheep with acute onset respiratory disease and 36 adult sheep with respiratory diseases associated with weight loss including ovine pulmonary adenocarcinoma (15) chronic suppurative pulmonary disease (6 cases), fibrinous pleurisy (2 cases), pleural/superficial lung abscesses (10 cases) and pyothorax (3 cases).

Results - Ultrasonographic examination of the chest was most helpful in the definitive diagnosis of pleural/superficial lung abscesses where the anechoic areas containing multiple hyperechoic dots bordered distally by a broad hyperechoic capsule were readily detected but generated no adventitious lung sounds. Daily treatment with procaine penicillin for 42 days was successful in all six sheep identified with pleural/superficial lung abscesses measuring 2-8 cm in diameter; only one of four sheep with more extensive lesions, and one of three unilateral pyothorax cases recovered. Pleural frictions rubs were not heard in cases of marked fibrinous pleurisy or when there were adhesions associated with pleural/superficial lung abscesses. Lesions of ovine pulmonary adenocarcinoma (OPA) were sharply demarcated hypoechoic areas extending 6-8 cm into the lung parenchyma in the cranio-ventral lung lobes and had the sonographic appearance of liver but such lesions could not accurately be delineated by auscultation findings. Despite its chronic nature, OPA was the only identified risk factor predisposing to septicaemia in nine sheep.

Discussion - Accurate identification and distribution of pleural and superficial lung pathology necessitated ultrasonographic examination; auscultation failed to identify and delineate lesions. With some experience, systematic ultrasound examination of the ovine chest takes no more than 5 minutes.

Conclusion - Long-term penicillin therapy was successful in 7 of 10 cases of pleural/superficial lung abscesses. Treatment of septicaemia secondary to OPA was unsuccessful in the first five sheep and could not subsequently be justified for welfare reasons once the extensive lung tumour pathology had been identified ultrasonographically.