Squamous-cell carcinoma of the vulva in Merino sheep.

Squamous-cell carcinoma of the vulva was observed in 3.1% of Merino ewes up to 3 years old. It is suggested that this high incidence of tumours was related to increased exposure of the perineal region to direct sunlight. It occurred in a group of sheep where short docking of tails and a radical surgical procedure to reduce cutaneous myiasis (Mules' operation) both led to greater exposure of the perineal region. The perineum was also subject to scarring from the operation and to application of organophosphate compounds to control cutaneous myiasis.