Fig. 1

a–i Ultrasound recording of the chest of sheep 15733 a-d: right side, e–i left side. Dorsal is to the left of the image. Scale (cm) is on the right margin. The blue bar represents 2 cm. At day 0 no ultrasonographic abnormality was detected in the right lung. a Week 6: The hyperechoic line representing the visceral pleura (normal lung surface) is clearly visible and contains two 2 mm hypoechoic circles (arrows). b Week 9: A poorly-defined hypoechoic triangular area extends about 20 mm from the visceral pleura in the ventral lung field. c Week 11: hypoechoic area extends about 20 mm. d Week 13: hypoechoic area extends about 30 mm. e Day 0: A poorly-defined, hypoechoic triangular area extends about 20 mm from the visceral pleura. Several 2–5 mm hypoechoic circular areas occur immediately ventral to the triangular lesion. f Week 6: The hypoechoic triangular area extends about 30 mm and is considerably wider than on day 0 such that no normal lung surface is visible. g Week 9: The hypoechoic triangular area extends about 30 mm and its base fills the field of view. h Week 11: The hypoechoic triangular area extends about 45 mm and its base fills the field of view. i Week 13: The hypoechoic area extends more than 50 mm from visceral pleura and fills the field of view. j Necropsy at week 13 showed OPA affecting the middle lobe of the right lung. k Consolidation affecting a large proportion of the ventral aspects of the left lung lobes. Fibrous pleurisy is also present, indicative of prior inflammation and suggesting a secondary bacterial infection. l Photomicrograph of haemotoxylin and eosin stained lung section from sheep 15733 showing typical lesions of OPA