This is a superficial bacterial (Pseudomonas aeruginosa) infection of wooled skin that causes crusty, colourful lesions along the backline. Certain strains of bacteria act in moist conditions to stain wool close to the skin.
Young, shorn sheep are most susceptible, especially in wet, warm conditions. Affected sheep are also susceptible to fly strike.
The skin and wool of the back are stained with hues of grey, green, yellow and brown but sometimes blue and orange, depending on the strain of bacteria present.
Diagnosis is usually by gross examination but a skin biopsy from an affected area may be submitted in buffered formalin if necessary.
No treatment is necessary unless flystrike occurs.
Preventative measures are usually unwarranted in the live export trade where fleece quality is usually unimportant.