The reason of the practice

Mulesing is a protection against flystrike

The Mules operation has been introduced to prevent flystrikes that are a great danger for sheep’s health. Those strikes, also called myiases, are pathological infection by parasitic fly larvae feeding on the host’s living tissue. This leads to both mechanical and chemical damage to the tissue, to a substantial physiological stress response of the animal and even to septicemia and death within days if left untreated. The incidence of flystrike can be up to 100% in unmulesed Merino sheep under favorable conditions (Lee & Fisher, 2007). Different studies on the efficiency of mulesing have shown a decrease of the incidence of flystrike by 90 to 100% in mulesed sheep. This protection is realized through the production of a new bare skin, resistant to the strikes and a reduction of the secretions that attract flies.

Lucilia cuprina is the fly responsible for the flystrike

The main fly responsible for the flystrikes is called Lucilia cuprina. It is also know as the sheep blowfly or green bottle fly. It forms four developmental stages: egg, larva, pupa and adult. The adult female fly is attracted by the excessive wrinkle skin of merino sheep that trap feces, urine and sweat. She lays about 200 eggs on the wet fleece. Those eggs usually hatch into larvae in 8-24 hours depending on the weather. The larvae, also called maggots, invade the living tissue and pass though 3 stages over 3-6 days after which they drop into the soil to transform in pupae and adults. The larvae activity results in invasive lesions and a modification of the fleece that becomes darker and develops a foul odor, which appears to act as a chemo-attractant for subsequent infestations.

The other advantages of the Mules operation

According to James (2006) and Philips (2009), mulesing has other advantages than the only protection against flystrike. It also

  • reduce wool staining and dags (accumulation of faeces on the wool, generally due to diarrhea)
  • reduce the need for crutching and dagging (removal of dags)
  • reduce the labor for inspecting the flock and treating struck animals
  • reduce the amount of chemical used to control flystrike and thus the residues on the wool
  • improve the ease of shearing and crutching and allow to time shearing to optimize wool quality rather than to minimize flystrike incidence.



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