Mulesing is a controversial method of treating sheep to protect them from infestation by the so-called "sheep blowfly". These flies lay their eggs in the warm, dirty and poorly ventilated skin folds of the sheep's anal and genital regions. After hatching, the fly maggots eat their way into the animals, often leading to infection or even death. In the method, which is common in Australia and New Zealand, pieces of flesh around the anus and genital region are cut out of lambs in the 8-12 week after birth to prevent nesting. This creates scarred tissue, which prevents the parasites from settling. Due to the lack of technical expertise, lack of anesthesia and poor or inadequate wound care after treatment, this method, which is also used in the breeding of Merino sheep, should be viewed critically. In New Zealand, this process has largely been discontinued on a voluntary basis since 2010.
Wool from Uruguay and Patagonia is considered mulesing-free, as flies do not occur in this region.