Blowfly strike is a common and serious issue for sheep, caused by the invasion of live tissue by fly larvae. This condition is caused by green, blue, and black bottle flies. With greenbottles initiating strike on living sheep with soiled fleece or wounds, while blue and blackbottles target already struck or damaged areas.
Blowfly populations, most active during summer, now pose a risk from March to December in some lowland areas due to climate change. The life cycle, from egg to adult, can be less than 10 days in ideal conditions. Sheep affected by blowfly strike exhibit disrupted grazing and rapid weight loss if left untreated.
Female blowflies lay eggs on dead animals or soiled fleeces. Eggs hatch into larvae within 12 hours, maturing into maggots in as little as three days. Mature maggots drop to the ground and emerge as flies in three to seven days between May and September. They can over-winter in the soil as pupae, emerging in spring.
Maggots cause damage by feeding on an animals skin and muscle, secreting enzymes. Blue and blackbottle flies are then attracted to the decomposing tissue. Toxins and ammonia from maggots are absorbed into the bloodstream, causing illness and sometimes death.
Blowfly strike is a major animal welfare concern. In the UK, about 1.5% of ewes and 3% of lambs are affected annually, despite preventive measures. This number would be higher without control measures. Flystrike of foot lesions can also cause severe lameness (NADIS).
Signs of flystrike:
- Isolation from flock.
- Discoloured wool.
- Agitation, kicking or nibbling the affected area.
- Disturbed grazing.
- Tissue decay.
- Toxaemia (blood poisoning from a local bacterial infection).
Prevention and control:
Apply preventative treatments at the beginning of the main blowfly season. Product choice depends on the sheep, its age, the withdrawal periods as well as shearing and lambing dates. (More than one application may be required).
Minimise soiling of fleece. Dagging, crutching and shearing, together with an effective worm control strategy, are important ways risk can be reduced. Tail docking is also used to reduce the incidence of strike in lowland flocks.
Treat lameness promptly. Flies are attracted to wounds caused by footrot and to the feet themselves; foot strikes can cause severe lameness so prompt treatment is required.
Reduce fly population. If the fly population is controlled early in the year, there is a reduced challenge as the grazing season progresses.
- Fly traps have been shown to reduce strike by 80% in a season.
- Dispose of deadstock in a quick manner.
- In high risk periods, consider grazing more exposed pastures that are less favourable to flies.
Recording remedies and treatments on the Herdwatch App
Simplify your medicine records using the Herdwatch app, you can record any treatment you administer from your mobile phone. With the administration of whole flock treatments such as dipping or CLiK, speed up the process with the ‘select all’ button.
How do I record a treatment?
>Click the orange plus button in the app.
>Select sheep treatment.
>Select treatment only/from remedy cabinet.
>Select your treatment, click next.
>Select the administration date, click ok.
>Fill out the required information, click next.
>Select the tag numbers you have treated (or select all), click save.
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