Fly strike in sheep

Flystrike in sheep is a myiasis condition, in which domestic sheep are infected by one of several species of flies which are external parasites of sheep.

Causes

Fly strike in sheep is a condition where parasitic flies lay eggs on soiled wool or open wounds. After hatching, the maggots, bury themselves in the sheep’s wool and eventually under the sheep’s skin, feeding off their flesh. Once the larvae develop, flies continue to deposit eggs on to new or already infected sheep, starting the infection process over again. Sheep display symptoms such as agitation, odour and matted fur, all which further encourage the attraction of flies. Fly strike can be lethal for sheep due to ammonia poisoning.^[1]

Fly strike is problematic in Australian agriculture, not only causing loss or degradation of stock, but also requiring expenditure of both money and time for effective management. In Australia, Lucilia cuprina causes about 90% of infestations, and Chrysomya rufifacies is the most common secondary pest the targets wounds caused by L. cuprina.^[2]

Identification of infected sheep

Flystruck sheep is identified in the mob through characteristic green patches in the sheep's fleece, usually around the bottom area, or at the site of an open wound, where wool can create a damper area which is more attractive to flies. In male sheep the penile region is also a common area for flystrike to occur. When the mob settled, infected sheep will display signs of irritaion such as stamping their feet or turning to nibble their body. Area of flystrike have a strong odour and in severe cases, the sheep's wool can begin to shed. ^[3] Fly strike is more likely to be found in favorable environmental conditions such as temperatures between 15–38 °C (59–100 °F), recent rain, and wind speeds below 9 kilometres per hour (5.6 mph).^[2]

Treatment

If infested, animals are removed from the mob and all wool in and around roughly a 1 cm or larger radius of the discoloured area is clipped. The area is treated with insecticide to kill the maggots. Clippings are collected after removal in a maggot-proof bag and left closed in the sun, to ensure that no other animal is infected.^[4]

Prevention

There are several preventative measures which are used to reduce the occurrence of flystrike in sheep mobs, these include:^[2]

• Controlling intestinal parasites to prevent scours and a suitable surface for flystrike
• Scheduled shearing and crutching
• Removing the tails of lambs at weaning
• Mulesing
• Preventative chemical treatments when infestation risk is high
• Breeding for traits that reduce the likelihood of infestation

None of these measures completely stop the occurrence of fly strike in sheep, and regular treatment is still necessary.^[5]

See also

• Sheep dip
• Mange
• Sarcoptes scabiei

References