Mulesing is the surgical mutilation, without the use of painkillers, of Merino sheep. Skin from the animal's tail area is sliced away with hand shears, leaving a bleeding, gaping wound. The stated purpose of mulesing is to create a large area of scar tissue devoid of wool, keeping the rear end of the sheep cleaner and therefore reducing the likelihood of flystrike.

Mulesing is extremely painful, and lambs have been seen to demonstrate abnormal behaviour indicative of extreme pain for days afterwards, with the wounds taking up to a month to heal.

New Zealand has a flock of around two million Merino sheep. Around half used to be mulesed but the Merino industry has officially voluntary prohibited the practice since the end of 2010. It has not yet been made illegal. The Ministry of Primary Industries has stated they intend to introduce regulations in 2018 to finally ban the practice.

In Australia, over 20 million sheep are mulesed each year. Their wool industry was thrown into turmoil after exposés of the practice horrified the public. Australian Merino wool is commonly available in New Zealand.