Here's an in-depth article about the practice of mulesing sheep in Australia. The practice has received much criticism.
It refers to the slicing of a patch of skin from the rear of Australian merino sheep to prevent flystrike. Often done without anaesthetic - due to reasons such as cost and previous unavailability - the procedure is aimed at removing permanently the wrinkly skin that otherwise becomes a moist haven for blowflies to lay eggs.
Photo by ariehsinger.