Blowflies are the most widespread ectoparasite affecting sheep in the UK, with surveys showing that every year 80% of flocks will have one or more cases of strike. If not properly controlled, this will result in serious welfare problems and reduced profitability in up to 500,000 sheep annually, says the Sustainable Control of Parasites in Sheep (SCOPS) programme.
In the UK, blowfly strike is usually caused by the greenbottle fly. The females are attracted by the odour of decomposing matter such as wounds, soiled fleece or dead animals. Each female lays up to 250 eggs which hatch after about 12 hours. After 3 days the mature larvae drop off the sheep and pupate in the soil. Blowfly strikes usually occur in waves. The first fly lays her eggs and the odour from this strike attracts other flies. When the populations of larvae become overcrowded they will attack the living tissue of the sheep. The first signs in affected sheep are a patch of discoloured wool and agitation. Rapid diagnosis and treatment are essential.
Traditionally, we expect to see blowfly strike between May and September but with changing weather patterns, lowland flocks are at risk from March through to December. With increasing flock sizes and the need to rationalise labour use to improve profitability, flocks must have a plan that will provide protection during the risk period and fit with the need to control other parasites.
Blowfly strike can be prevented through the application of an appropriate product before a period of challenge. The table below contains a list of the products currently licensed for this use.
REMEMBER, when using these products ALWAYS read the manufacturers instructions on dose rate, storage and withdrawal periods. Check application equipment is working properly and is calibrated. Replenish dips according to instructions and follow safety guidelines.
Good management and planning can help to reduce the risk of strike occurring. Most strikes (over 70%) occur around the breech or tail where there is faecal and/or urine soiling as these are very attractive to the flies, with the rest on the body or in the feet.
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